essay on uses of dams

• Biology Article
• Advantages Of Dams

Advantages of Dams

Dams are said to be an important source of water supply and of high importance for various other reasons. They supply the water for various means including domestic use, irrigation purposes and also for industrial uses.

Dams are also involved in hydroelectric power generation and in river navigation. The application of these dams is much more important in daily activities including cooking, cleaning, bathing, washing,  drinking water, for gardening and for cultivation purpose.

The big dams and the reservoirs also provide recreational areas for the purpose of fishing and also boating. They also cater insecurity needs of humans by reducing or preventing floods. During the times of excess flow of water, the dams store the water in the reservoir; later they release that water during the times of low flow, also when the natural flows of water are inadequate to meet the demand. When engineers design and also maintain the dams, they are keenly expected to make sure to keep all purposes in their mind.

The advantages of dams are numerous, and that is the reason so much money and work goes into building and maintaining them. Some of the advantages are:

• Electricity is produced at a constant rate with the help of hydroelectricity or hydroelectric power.
• If there is no need for electricity, then the sluice gates can also be closed to stop the generation of electricity. Water can also be saved for future use when the demand for electricity is high hence the usage of water remains judicious.
• Dams are designed by well-qualified engineers to last several decades and also to contribute to the generation of electricity for several years or even decades to come.
• The lake or reservoir which forms behind the dam can also be used for  irrigation purposes, water sports or even as other forms of pleasurable activities. A few large dams such as the Bhakra Nangal dam present in India are tourist attractions.
• When used, the electricity produced by the dams does not even generate greenhouse gases and therefore they do not pollute the atmosphere.

Also Read:  List of Largest dams in India

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ENCYCLOPEDIC ENTRY

Hydroelectric energy.

Hydroelectric energy is a form of renewable energy that uses the power of moving water to generate electricity.

Earth Science, Geography, Physical Geography

Slovenian Hydroelectric Dam

Damed river in a valley marked with agricultural fields along the flood plains surrounded by rolling hills.

Photograph by spiderskidoo/Getty

Hydroelectric energy , also called hydroelectric power or hydroelectricity , is a form of energy that harnesses the power of water in motion—such as water flowing over a waterfall—to generate electricity. People have used this force for millennia. Over 2,000 years ago, people in Greece used flowing water to turn the wheel of their mill to ground wheat into flour.

How Does Hydroelectric Energy Work?

Most hydroelectric power plants have a reservoir of water, a gate or valve to control how much water flows out of the reservoir , and an outlet or place where the water ends up after flowing downward. Water gains potential energy just before it spills over the top of a dam or flows down a hill. The potential energy is converted into kinetic energy as water flows downhill. The water can be used to turn the blades of a turbine to generate electricity, which is distributed to the power plant’s customers.

Types of Hydroelectric Energy Plants

There are three different types of hydroelectric energy plants, the most common being an impoundment facility. In an impoundment facility, a dam is used to control the flow of water stored in a pool or reservoir . When more energy is needed, water is released from the dam. Once water is released, gravity takes over and the water flows downward through a turbine . As the blades of the turbine spin, they power a generator.

Another type of hydroelectric energy plant is a diversion facility. This type of plant is unique because it does not use a dam. Instead, it uses a series of canals to channel flowing river water toward the generator-powering turbines .

The third type of plant is called a pumped-storage facility. This plant collects the energy produced from solar, wind, and nuclear power and stores it for future use. The plant stores energy by pumping water uphill from a pool at a lower elevation to a reservoir located at a higher elevation. When there is high demand for electricity, water located in the higher pool is released. As this water flows back down to the lower reservoir, it turns a turbine to generate more electricity.

How Widely Is Hydroelectric Energy Used Around the World?

Hydroelectric energy is the most commonly-used renewable source of electricity. China is the largest producer of hydroelectricity. Other top producers of hydropower around the world include the United States, Brazil, Canada, India, and Russia. Approximately 71 percent of all of the renewable electricity generated on Earth is from hydropower.

What Is the Largest Hydroelectric Power Plant in the World?

The Three Gorges Dam in China, which holds back the Yangtze River, is the largest hydroelectric dam in the world, in terms of electricity production. The dam is 2,335 meters (7,660 feet) long and 185 meters (607 feet) tall, and has enough generators to produce 22,500 megawatts of power.

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Related Resources

Dams and Reservoirs

Overview of Dams and Reservoirs

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• Physical Geography
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• M.A., Geography, California State University - East Bay
• B.A., English and Geography, California State University - Sacramento

A dam is any barrier that holds back water; dams are primarily used to save, manage, and/or prevent the flow of excess water into specific regions. In addition, some dams are used to generate hydropower. This article examines man-made dams but dams can also be created by natural causes like mass wasting events or even animals like the beaver.

Another term often used when discussing dams is reservoir. A reservoir is a man-made lake that is primarily used for storing water. They can also be defined as the specific bodies of water formed by the construction of a dam. For example, the Hetch Hetchy Reservoir in California’s Yosemite National Park is the body of water created and held back by the O’Shaughnessy Dam.

Types of Dams

One of the most common types of major dams is the arch dam. These masonry or concrete dams are ideal for narrow and/or rocky locations because their curved shape easily holds back water via gravity without the need for a lot of construction materials. Arch dams can have one large single arch or they can have multiple small arches separated by concrete buttresses. The Hoover Dam which is on the border of the U.S. states of Arizona and Nevada is an arch dam.

Another type of dam is the buttress dam. These can have multiple arches, but unlike a traditional arch dam, they can be flat as well. Normally buttress dams are made of concrete and feature a series braces called buttresses along the downstream side of the dam to prevent the natural flow of water. The Daniel-Johnson Dam in Quebec, Canada is a multiple arch buttress dam.

In the U.S., the most common type of dam is the embankment dam. These are large dams made out of soil and rock which use their weight to hold back water. To prevent water from moving through them, embankment dams also have a thick waterproof core. The Tarbela Dam in Pakistan is the world’s largest embankment dam.

Finally, gravity dams are huge dams that are constructed to hold back water using only their own weight. To do this, they are constructed using extensive amounts of concrete, making them difficult and expensive to build. The Grand Coulee Dam in the U.S. state of Washington is a gravity dam.

Types of Reservoirs and Construction

The first and usually largest type of reservoir is called a valley dammed reservoir. These are reservoirs that are located in narrow valley areas where tremendous amounts of water can be held in by the valley’s sides and a dam. The best location for a dam in these types of reservoirs is where it can be built into the valley wall most effectively to form a water tight seal.

To construct a valley dammed reservoir, the river must be diverted, usually through a tunnel, at the start of work. The first step in creating this type of reservoir is the pouring of a strong foundation for the dam, after which construction on the dam itself can begin. These steps can take months to years to complete, depending on the size and complexity of the project. Once finished, the diversion is removed and the river is able to flow freely toward the dam until it gradually fills the reservoir.

Dam Controversy

In addition, the creation of a reservoir requires the flooding of large areas of land, at the expense of the natural environment and sometimes villages, towns and small cities. The construction of China’s Three Gorges Dam , for example, required the relocation of over one million people and flooded many different archaeological and cultural sites.

Main Uses of Dams and Reservoirs

Another major use of dams is power generation as hydroelectric power is one of the world’s major sources of electricity. Hydropower is generated when the potential energy of the water on the dam drives a water turbine which in then turns a generator and creates electricity. To best make use of the water’s power, a common type of hydroelectric dam uses reservoirs with different levels to adjust the amount of energy generated as it is needed. When demand is low for instance, water is held in an upper reservoir and as demand increases, the water is released into a lower reservoir where it spins a turbine.

Some other important uses of dams and reservoirs include a stabilization of water flow and irrigation, flood prevention, water diversion and recreation.

To learn more about dams and reservoirs visit PBS's Dams Site .

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• Published: 18 January 2021

Role of dams in reducing global flood exposure under climate change

• Julien Boulange   ORCID: orcid.org/0000-0003-2167-8761 1 ,
• Naota Hanasaki   ORCID: orcid.org/0000-0002-5092-7563 1 ,
• Dai Yamazaki   ORCID: orcid.org/0000-0002-6478-1841 2 &
• Yadu Pokhrel   ORCID: orcid.org/0000-0002-1367-216X 3  

Nature Communications volume  12 , Article number:  417 ( 2021 ) Cite this article

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• Climate-change impacts

Globally, flood risk is projected to increase in the future due to climate change and population growth. Here, we quantify the role of dams in flood mitigation, previously unaccounted for in global flood studies, by simulating the floodplain dynamics and flow regulation by dams. We show that, ignoring flow regulation by dams, the average number of people exposed to flooding below dams amount to 9.1 and 15.3 million per year, by the end of the 21 st century (holding population constant), for the representative concentration pathway (RCP) 2.6 and 6.0, respectively. Accounting for dams reduces the number of people exposed to floods by 20.6 and 12.9% (for RCP2.6 and RCP6.0, respectively). While environmental problems caused by dams warrant further investigations, our results indicate that consideration of dams significantly affect the estimation of future population exposure to flood, emphasizing the need to integrate them in model-based impact analysis of climate change.

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Introduction.

Global warming is expected to increase flood risk by altering the distribution, variability, and intensity of precipitation events 1 , 2 . While global estimates of populations exposed to river flooding vary widely across studies, a 4–20 fold increase by the end of the 21 st century is commonly predicted 3 , 4 , 5 . To mitigate the destructive potential of floods and maximize water availability for human consumption, an estimated 2.8 million dams 6 have been constructed globally with a total water impoundment capacity ranging from 7,000 to 10,000 km 3 , which represents over one-sixth of the annual continental discharge to global oceans 7 , 8 , 9 . Currently, about half of the planet’s major river systems are regulated by dams 10 , 11 and only 23% of rivers worldwide flow uninterrupted to the ocean 6 . By regulating water flow, dams generally alter the frequency, duration, and timing of annual flooding events 12 . With more than 3,700 major dams planned or under construction worldwide 13 , understanding the role of dams in climate impact studies has become increasingly important. Previous studies on flood prediction, however, have neglected the role of dams 3 , 14 due to data scarcity 15 , difficulties in parameterizing reservoir outflows, and challenges in implementing features of dams that function at a scale smaller than those accounted for by global-scale models.

Previous global-scale analyses of floods have reconstructed historical flood patterns 16 , 17 to forecast future floods considering climate change 3 , 14 and/or socio-economic development factors 18 , 19 . A key conclusion of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) was that the number of people exposed annually to the equivalent of a historical 100-year river flood was projected to triple when compared to high and low emission scenarios. However, despite the regulation of most large rivers by dams, the extent to which their alterations of river and floodplain dynamics interacts with flooding, and the exposure of populations to floods in response to climate change remains largely unknown since dams have not been physically integrated into global flood-impact studies 3 , 14 , 15 , 20 . The few studies that have accounted for dams and/or flood protection have underscored the importance of considering dam-induced changes in streamflow characteristics in flood-hazard modelling 21 , 22 , 23 . In the contiguous United States (CONUS), dams are reported to reduce total flood exposure by 9% (protecting approximately 590 million people) owing to the medium to high dam attenuation effects on the 100-year return period discharge of 62% of CONUS hydrological units 22 .

Here, we provide the first global assessment of the role of dams in reducing future flood risk under climate change by using a modelling framework that integrates state-of-the-art global hydrological model with a new generation of global hydrodynamics model. Specifically, the modelling framework quantifies changes in the frequency of historical 100-year return period floods when dams are considered and estimates the global population at a reduced risk of flood exposure. Throughout this study, a flooding event is defined as extreme discharge associated with a 100-year return period (probability). We specifically investigated flood frequency (number of floods per year), the associated maximum flooded area, and populations exposed to these floods.

Streamflow regulation

Robust and reliable estimates of future river floods rely on two critical components: accurate reproduction of river discharge and appropriate prediction of floodplain inundation dynamics. In this study, we used two different models to simulate these critical processes globally. River discharge considering dams was simulated by H08, while flood inundation dynamics were simulated by the CaMa-Flood model. H08 is a global hydrological model that considers human interactions with the hydrological cycle. CaMa-Flood is an advanced river hydrodynamics model with an emphasis on efficient flow computation at the global scale (see Methods). Two global flood simulations were performed: one considering dams and one not considering dams. In total, four bias-corrected global circulation models (GCMs) combined with three radiative forcing scenarios (historical, RCP2.6, and RCP6.0) were used to force the models (see Methods).

The H08 model has been widely used and validated in global studies and accurately reproduces monthly river discharge in basins heavily affected by anthropogenic activities 24 . At the global scale, the H08 model has been benchmarked against other global hydrological models (GHMs) and has performed relatively well for reproducing the magnitude of high flows associated with different return periods 25 . H08 has also been calibrated and validated at finer spatial and temporal resolutions in multiple regional analyses, including the Chao-Phraya basin, the Ganges–Brahmaputra–Meghna basin, and Kyushu Island, among others 26 , 27 , 28 . Critical to these faithful discharge reproductions is the scheme used for dam operations. While improvements to the dam operation scheme implemented in H08 have been recently proposed 29 , 30 , it is still regarded as the benchmark to beat, given its ability to capture observed reservoir storage variation with high accuracy 31 . CaMa-Flood has also been extensively used and validated. It is capable of faithfully reproducing historical flood patterns 32 , 33 , 34 and daily measurements at river gauging stations across the globe 33 , partly owing to the integration of satellite-based topography data 35 . While both models have been widely used for climate impact assessments, they have never been coupled to analyze global-scale floods, leaving a gap in our understanding of the potential role of dams in reducing future flood risks. While the GCMs employed in this analysis were not assimilated, and consequently do not reproduce the exact timing of historical weather events, we nevertheless confirmed that our coupling framework can satisfactorily reproduce observed monthly discharges before and after dam construction (see Supplementary Figs.  13 – 23 ) and that its predicted maximum discharges in 33 large basins were reasonably similar to available observations (see Supplementary Fig.  24 ). We further compared global patterns of future floods with a previous publication 3 (Supplementary Figs.  1 and   5a, b ). We also compared the historical and predicted populations exposed to 100-year floods with information from published literature and a public database (see Supplementary Table  2 and Supplementary Note  1 ).

Population exposure to floods

Results indicate that, driven by climate change, the risk of floods will increase in the future. However, owing to the implementation of dams in our simulations, on average (range from the first and third quartiles in bracket represent uncertainty from the GCM ensemble), populations exposed to flooding below dams decreased by 16.3% (5.7–30.7%) in the RCP2.6 scenario and 12.8% (4.2–27.5%) in the RCP6.0 scenario, respectively, compared to the RCP simulations not considering dams (over 2006–2099, see Fig.  1 ). The decrease in the number of people exposed to floods due to the implementation of dams was highest during the last decade of the 21 st century for both RCPs. On average, 9.1 (4.6–18.1) million people were exposed to river floods in RCP2.6 (no dams) compared to 7.2 (3.5–15.1) million people in the simulation with dams. In the RCP6.0 scenario, the population exposed to river floods increased considerably to 15.3 (8.3–27.2) million and 13.4 (7.3–24.3) million for the simulations without and with dams, respectively. Large differences, consistent across experiments, in the number of people exposed to floods between the GCMs were apparent (Fig.  1b ). When population growth was taken into consideration using Shared Socioeconomic Pathways (SSPs) (see Methods), accounting for dams reduced populations exposed to flooding below dams by 20.6–32.0% for RCP2.6 and 7.0–16.8% for RCP6.0 (lowest and highest values across the five SSPs).

a 5-year moving averages of the population living below dams exposed to the historical 100-year river flood for historical (grey line) and future simulations for 2 RCPs and experiments (colour lines). The uncertainty range represent the spread among GCMs. b The 95 th and 5 th range (whiskers), median (horizontal lines in each bar), and 1 st and 3 rd quartiles (height of box) and individual mean values among GCMs (markers) of the population exposed to the historical 100-year flood for grid-cells located below dams over the 2070–2099 period.

Return period of future floods

Downstream of dams, historical 100-year floods occurred less frequently in the experiment considering dams than in the experiment with no dams for: (on average and ± standard deviation across GCMs), 66.6 ± 4.2% and 60.8 ± 12.7% of the grid-cells in RCP2.6 and RCP6.0, respectively (Fig.  2 , Supplementary Fig.  5c ). These results are similar to other regional- and country-scale analyses. For example, in the US, medium or large dam-attenuation effects were reported for 62% of hydrologic units 22 . Likewise, a study in Canada revealed that dams totally prevented flows with a return period greater than the historical 10-year recurrence 36 (see additional comparison with existing studies in Supplementary Note  3 ). Particularly prominent reductions in future flood frequency were observed along major sections of rivers containing multiple high-capacity dams (e.g. the Mississippi, Danube, and Paraná; see Supplementary Fig.  2 ). Reductions in 100-year flood frequencies in the experiments involving dams decreased moving downstream, becoming relatively small (or negligible) at the river mouth (e.g. in the Amazon, Congo, and Lena; see grey cells in Fig.  2 ). In a few locations (blue cells in Fig.  2 ), the presence of dams increased the frequency of historical 100-year floods compared to experiment without dams (6.7 ± 2.4% and 4.6 ± 1.1% for RCP2.6 and RCP6.0, respectively). This behaviour was connected to sporadic overflow events referred to as the pulsing effect by Masaki et al. 37 and has been documented for some rivers in the US 23 . Although water released from dams was regulated through the majority of the simulation period, pulsing events can result in a dam failure to prevent flooding, distorting the distributions of extreme discharge, and compromising the fitting of the extreme discharge to a Gumbel distribution (see Methods). In such cases, the definition of the 100-year flood is rather ambiguous, and while great efforts are made to prevent overflow 29 , not all are reflected in the generic scheme for dam (see Methods). Note that since the lead time before major storms is generally too short for preventive dams emptying, pulsing may not be totally averted in global dam simulations.

Grid-cells belonging to Köppen–Geiger regions BWk , BWh (hot and cold desert climates, respectively), and EF (ice cap climate) and for which the 30-year return period discharge was lower than 5 m s −1 were systematically screened out (see Methods). The case for representative concentration pathway (RCP) 6.0 is shown (RCP2.6 available in Supplementary Fig.  5c ).

Evolution of future floods for individual catchments

Median changes in the occurrence of historical 100-year river floods and the maximum flooded areas in the experiment considering dams relative to the experiment not considering dams were computed over the 2070–2099 period for 14 catchments (see Methods for the selection of catchments). Figure  3 indicates that the historical 100-year floods occurred less frequently in the experiment with dams, decreasing, on average, across catchments by 36.5% (26.6–49.1%) for RCP2.6 and 35.5% (28.8–46.6%) for RCP6.0. Similarly, the maximum flooded area in the catchments shrank on average by 22.5% (19.8–40.5%) and 25.9% (12.1–34.5%), for RCP2.6 and RCP6.0, respectively. These reductions in the occurrence of 100-year floods and maximum flooded areas were robust to the choice of extreme discharge indices used for identifying flood events (see Methods), with the exception of two catchments that experienced pulsing from dams (Supplementary Fig.  7 ). We note that by employing alternative extreme discharge indices (see Methods) to identify flood events, the eventual influence of pulsing events on the occurrence of 100-year floods and maximum flooded areas was largely filtered.

a Occurrence of the historical 100-year river flood and, b annual maximum flooded area over the period 2070–2099, given two experiments (with and without dams), and tow representative concentration pathways (RCP). The box-and-whisker plots include the 95 th and 5 th range (whiskers), median (horizontal lines in each bar), and 1 st and 3 rd quartiles (height of box) of the annual values obtained for all four global circulation models.

The 100-year return extreme discharge expected in the future (2070–2099) was calculated for all combinations of RCPs and experiments (Supplementary Fig.  8 ) along the main river of the 14 catchments. Downstream of dams, the experiment considering dams always produced a lower 100-year discharge than that produced by the experiment not considering dams. For catchments located in regions where annual precipitation and/or snowmelt is forecast to decrease in the future (the Mississippi, Volga, and Euphrates; see Supplementary Figs.  1 and  8a, c, d ), the RCP2.6 simulations produced higher 100-year discharges than those in the RCP6.0. However, simulations employing the RCP6.0 scenario and the experiment not considering dams generally produced the highest 100-year discharges. For catchments containing few dams on the mainstem river, future 100-year return extreme discharges in both experiments (with and without dams) were similar at the river mouth (Supplementary Fig.  8i, k, l, m, n ). However, in other catchments, the 100-year extreme discharges were clearly reduced in the experiments considering dams (Fig.  3 and Supplementary Fig.  7 ), resulting in reduced flood exposure to populations residing downstream of dams. In addition, the reductions in 100-year extreme discharge in the Amazon, Congo, and Mekong rivers were relatively small due to the small cumulative storage capacity of the mainstem dams compared to the discharge volume generated in these basins.

Explicitly considering dams in climate-impact studies of floods significantly offsets the population size exposed to river floods. Downstream of dams at the end of the 21 st century, a 100-year flood was, on average, indicated to occur once every 107 (79–168) years for RCP2.6 and once every 79 years (55–103) in the experiments not considering dams (see Supplementary Fig.  8 ). In RCP6.0, the historical 100-year flood occurred more frequently: once every 59 years (39–110) and 46 years (33–75) for the experiments considering and not considering dams, respectively (see Supplementary Fig.  8 ). In most catchments, dams reduced both the frequency of floods and the extent of flooded areas. Our findings were robust to the selection of indices used to identify floods although the pulsing effect of dams was identified as compromising estimates in some catchments. This problem could be partially mitigated by revising the reservoir operation method used in the present study by accounting for future precipitation variabilities and cascade-dams. Since our large-scale modelling considers daily precipitation, potential dam failure due to increased extreme precipitation events 38 (resulting in downstream flooding) is not fully considered here, nor are the construction and filling phases of a dam’s life cycle. Nevertheless, neglecting the morphological, environmental, and societal impact of dams 39 , our results imply that dams significantly decrease the risk of future global floods in terms of both frequency and intensity, protecting 1.4 (0.7–3.1) and 2.3 (0.8–3.7) million people at the end of the 21 st century, for RCP2.6 and RCP6.0, respectively.

The aging dam landscape faces new temperature, snow, discharge, and floods patterns that increase the risk of hydrological failure 40 , 41 . To maintain historical levels of flood protection in the face of climate change, new dam release operations will be required. In addition, precise and reliable hydro-meteorological forecasts will be invaluable for maximizing flood protection and avoiding untimely and excessive outflows. By focusing solely on the role of dams in reducing global flood exposure under climate change, the results of this study are perceived as over emphasizing the benefits of dams (see Supplementary Note  2 ). However, given the many negative environmental and social impacts of dams 39 , comprehensive assessments that consider both potential benefits and adverse effects are necessary for the sustainable development of water resources. Furthermore, future analyses of global flood risks would benefit from: addressing the disparities and uncertainties associated with global dam and river datasets (e.g. location, characteristics, networks); developing realistic future population projections that account for population behaviour; enhancing historical GCM scenarios by assimilating past observations; and archiving and referencing historical reservoir operations, streamflow, and inundation for robust model validation.

Two hydrological models were used in this study. H08 is an open-source global hydrological model (GHM) that explicitly considers human water abstraction from six major water sources including dams 24 . The reservoir operation scheme in H08 is a generic one; that is, it is not tailored to a specific site. A detailed description can be found in Hanasaki et al. 31 . Outflow from dams is computed in two steps: considering the water currently available in the reservoir, a provisional annual total release is computed, and is then adjusted every month according to changes in storage, inflow, and water demand below the dams. The algorithm distinguishes two classes of dams: irrigation and non-irrigation dams, which influences the computation of monthly water release. It should be noted that, while the storage capacity used in the simulations corresponded to that reported in the Global reservoirs and Dams database (GRanD), the actual storage capacity of dams is expected to be lower due to the allocation of dead and surcharge storages. As a result, the allocated dam storage in the present simulations is likely to have been overestimated. The most recent version of the H08 model, which participated in ISIMIP2b, was employed 24 . Simulations were carried out at a spatial resolution of 0.5° by 0.5°, and a 1-day interval.

CaMa-Flood is a new generation of global river routing model that relies on HydroSHEDS 42 topography to simulate floodplain dynamics and backwater effects by explicitly solving the local inertia equation 33 . The model was reported to outperform other GHMs for reproducing historical discharge 43 . The CaMa-Flood model requires only daily runoff as an input, and by computing the inflow from upstream cells and outflow to downstream, the evolution of water storage can be predicted. In this study, three output variables were used: the total discharge exiting a grid-cell (sum of river discharge and floodplain flow), the flooded area, and the flooded fraction of a grid-cell. To output the latter two variables, CaMa-Flood assesses whether water currently stored in a grid-cell exceeds the total storage of the river section. When this is the case, excess water is then stored in the floodplain, for which topography (dictated by HydroSHEDS) controls the flood stage (water level and flooded area).

To simulate the effects of water regulation due to anthropogenic activities on floodplain dynamics, the H08 and CaMa-Flood models were coupled because, in its current global version (v3.62), the global version of CaMa-Flood cannot simulate dam operations despite being essential for assessing flood risk. Hence, the H08 model is required for accurate forecasts of dam outflow. To ensure compatibility between the models, the river network originally used in CaMa-Flood was employed in both models. The coupling procedure is as follows: simulations with the H08 model are conducted; the daily runoff predicted by H08 is used as a forcing input in CaMa-Flood; in grid-cells containing major dam(s), 44 the river discharge produced by H08 (following the reservoir operating rule) is imposed onto the CaMa-Flood model (Supplementary Fig.  3a ); the difference in daily discharge between the two models due to water regulation is added to the hypothetical storage associated with every dam but without interacting with the river or floodplain to close the water balance.

For grid cells that are neither downstream nor upstream of dams (light blue locations in Supplementary Fig.  3 ), experiments considering and not considering dams produced the same discharge outputs. In contrast, for grid cells located below and above dams, the daily discharge simulated by the experiments considering dams can change compared to the experiments not considering dams due to water regulation (below dams) and the impossibility of the backwater effect and its propagation (above dams).

The four general circulation models (GCMs; GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, and MIROC5) implemented in the ISIMIP2b protocol participated in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). The forcing data consisted of precipitation, temperature, solar radiation (short and long wave downward), wind speed, specific humidity, and surface pressure which were bias corrected 45 and downscaled to a 0.5° by 0.5°-grid resolution. Here we used three radiative forcing scenarios: historical climate (1861–2005), and two future scenarios consisting of a low greenhouse gas concentration emission scenario (RCP2.6; 2006–2099) and a medium–high greenhouse gas concentration (RCP6.0; 2006–2099). Note that the historical climate scenario does not attempt to reproduce the exact day-to-day historical climate but rather gives a consistent evolution of the climate under a given climatic forcing.

Dam specifications (location, storage capacity, and construction year) are provided in GRanD 44 , 46 . The dams were georeferenced to the river network employed in CaMa-Flood, iteratively adjusting dam locations when necessary until the catchment areas of each dam reported in GRanD corresponded to ± 10% of the catchment area in CaMa-Flood 47 .

Experiments

For the future scenarios (RCP2.6 and RCP6.0), two experiments were considered. In the first experiment, dams were not implemented, therefore this simulation is analogous to the simulations conducted in previous studies 3 , 14 . In contrast, in the second experiment, the effect of major global dams on water regulation, hence floodplain dynamics, were considered. Due to water regulation, the future return period (in years) associated with the historical 100-year extreme discharge might change compared to that obtained for the experiment not considering dams (Supplementary Fig.  8 ). These potential differences were used to quantify the effect of dams on the potential reduction in the future return period of the historical 100-year flood.

The H08 model has been extensively validated in catchments located in India, the US, China, Europe, and South America for predicting river discharge, total water storage anomalies, groundwater, and water transfer 24 . Across these major catchments, the average Nash–Sutcliffe efficiency ( NSE ) obtained when comparing daily observed and simulated discharge was positive. Benchmarked against GHMs, H08 was reported to perform relatively well for reproducing historical daily discharges 25 . More relevant to the context of this study, the same study 25 highlighted that the H08 model was among the top four GHMs best able to reproduce the magnitude of extreme discharge and the maximum flows associated with different return periods.

The ability of the CaMa-Flood model to reproduce floodplain inundation was reported in the Amazon basin, where it performed well 33 . In addition, the discharges produced by CaMa-Flood have been evaluated against gauge observations in 30 major river basins 33 . CaMa-Flood has also been benchmarked against nine GHMs, including the H08 model, at 1701 gauge locations 43 . Generally, discharge simulations using CaMa-Flood produce lower and later peak discharges compared to those predicted by other GHMs, resulting in more accurate reproduction of observations 43 .

The quality of discharge data produced by nine GHMs, including the H08 model used in this study, was evaluated and compared against calibrated regional hydrological models in 11 large river basins 48 . While regional models generally outperformed GHMs in most regions, GHMs reproduced the intra-annual variability of water discharge reasonably well. Extreme discharges are strongly related to floods, 5 and the inclusion of human activity in hydrological simulations, such as in H08 has been reported to greatly improve the reproduction of hydrological extremes 49 . The predicted return period for the historical 100-year discharge obtained in the experiment not considering dams was compared to the literature. Global estimates of populations exposed to river floods were also compared to those reported in the literature (Supplementary Table  2 ). We evaluated how the coupled model reproduced river discharges before and after the implementation of dams at key locations. We separated our observation dataset into two parts: pre- and post-dam construction. We then compared our dam and no-dam simulations to the relevant observations. Supplementary Table  3 lists the dam locations of the dams and their key characteristics.

Definition of flood event and extreme discharge

We compared the frequency of historical (1975–2004) and predicted future (RCP2.6 and RCP6.0; 2070–2099) flood events using given two experiments: an experiment in which no dams were considered (analogous to previous studies 3 , 4 , 5 ), and an experiment considering global dams (Supplementary Fig.  2 ) 50 . Flood events were defined as the historical 100-year return extreme discharge, that is, the extreme discharge with a probability of exceeding 1/100 in any given year.

Two annual-extreme discharge indices were used in this analysis to assess the robustness of our findings expressed by the spread (or consistency) of results from multiple GCMs and extreme indices. We primarily focused on the maximum annual daily discharge ( P max ) since it is the preferred index used in the literature 3 , 4 , 5 , 14 . The alternative indicator is the annual 5 th percentile ( P 05 ) of daily discharge.

Before fitting the Gumbel distribution to estimate the 100-year river discharge, we initially compared the two series of extreme discharges in the dam and no-dam experiments. Run-of-the-river dams tend to alter the natural flow regimes only negligibly. For such locations, the fitted Gumbel distribution should be identical in both experiments. In contrast, in rivers heavily regulated by dams, it is possible that the extreme discharge series obtained for the experiment considering dams included many identical or tied values. We initially computed the absolute difference between the annual discharge extremes obtained by the simulation not considering dams minus the simulation considering dams and compared that difference to a given threshold (150 m 3  s −1 , or an annual difference of 5 m 3  s −1 between the extreme discharge generated for the experiments with and without dams). When the threshold was exceeded, the extreme discharge series were considered dissimilar and therefore treated separately. In contrast, when the threshold was not exceeded, the two extreme discharge series were considered similar and all data were pooled before moving to the fitting phase. We assessed the sensitivity of our results to alternative thresholds, with those results reported in Supplementary Table  1 .

Fitting of Gumbel distribution

The extreme discharges were first ranked in ascending order and fitted to a Gumbel distribution using the L-moment method 51 . As a result of the comparison protocol, the number of data to fit was either 60 (experiments with and without dams produced similar extreme discharges and were pooled) or 30 (experiments with and without dams produced different extreme discharges). The fitting process is identical to that described in detail in the Supplementary Note  2 of Hirabayashi et al. 3 .

Assessment of goodness of fit

The goodness of fit of the annual extreme discharge to the Gumbel distribution was assessed using the probability plot correlation coefficient test (PPCC) 52 . While other methods can be used to assess the goodness of fit of the Gumbel distribution, the PPCC has been reported to outperform most of them in terms of rejection performance 53 . The PPCCs were computed for all historical simulations and are reported in Supplementary Fig.  9 . A PPCC score close to 1 indicates that the distribution of the extreme series is well fitted by the Gumbel distribution. For a sample size of 30, the critical PPCC score at the 95 th level of significance was reported 52 to be approximately 0.96.

A bootstrap methodology was used to assess the influence of the 30-year samples on the fitted Gumbel distribution 54 . We generated 1000 bootstrap estimates for every GCM and all experiments. We did not explore all combinations of bootstrap estimates and GCMs due to the high computational cost (1012 estimates for a given year and a single experiment). Instead, we ranked the estimates in descending order before taking the average across GCMs (1000 estimates for a given year and a single experiment). While simple, this method has the advantage of reporting the broadest confidence intervals since the lowest and highest estimates among GCMs are averaged.

In the reported global maps, we masked grid-cells belonging to the Köppen–Geiger regions BWk (hot desert climates), BWh (cold desert climates), and EF (ice cap climates) which discharge corresponding to the historical 30-year return period was less than 5 m 3  s −1 (Supplementary Fig.  4 ). In such grid cells, flooding is not a problem due to the low volume of water discharge. As a result, the goodness of fit of the Gumbel distributions was generally low (as indicated by a low PPCC score in Supplementary Fig.  9 ).

Population exposure

The population dataset, created by the Socioeconomic Data and Applications Center (SEDAC), consists of the Gridded Population of the World (GPW, v4.11) for the year 2010 55 . The population was fixed at 2010 to assess only the effect of climate change on population exposure to floods. To increase the accuracy of our exposure assessment, the original 0.5° resolution flooding depths were downscaled to a resolution of 0.005°. The file containing flooding depth resulting from historical 100-year floods was constructed annually following a two-step procedure. First, we determined the 0.5° grid cells experiencing a 100-year flood as indicated by the annual discharge extreme exceeding the 100-year historical discharge extreme. Second, for such grid cells, we extracted the maximum annual flooding depth, while the flooding depth of other grid cells was set to zero. The files were then downscaled to a 0.005° resolution using routines implemented in CaMa-Flood 33 (see model description). Population exposure to river floods was assessed by overlaying the population and flooding-depth datasets. When flooding water was present in a 0.005° cell, the population within that cell was considered exposed to flooding.

We accounted for population growth in a separate analysis using population projections from 2006 to 2099 based on shared socioeconomic pathways (SSPs) 1 to 5 provided in the ISIMIP2b framework. The time-varying population datasets were first downscaled to a 0.005° resolution. Population exposure to flooding was then determined using the procedure described above.

Catchment selection

Catchments were selected by ensuring that downstream areas were wide, densely populated, and contained major dams. More specifically, the following criteria were used: at least 10 grid cells below dams, a population of at least 5 million residing on the entire main river channel, and the capacity of dams divided by their annual inflow averaged over the number of dams present on the main river channel had to be higher than 0.1. While 15 catchments initially fulfilled these criteria, the Nile catchment was removed from our analysis since a significant portion of its upper section falls within the Köppen–Geiger region BWh (Supplementary Fig.  4 ), which was (partially) screened out of the analysis. The locations of the remaining 14 catchments are given in Supplementary Fig.  6 .

Catchment flood analysis

The analysis consisted of two parts: identifying in which grid cells a flood occurred and extracting the corresponding flooded area for those cells. First, daily discharge, collected annually for the 2070–2099 period, in all grid-cells composing the catchments was converted to annual extreme discharges (considering two indices) and compared to the 100-year return extreme discharge. When the annual extreme discharge was higher than that of the historical 100-year return discharge, a flood was considered to occur in that year. Second, for grid cells where a flood occurred, the maximum flooded area of the grid cell was collected. Finally, we presented the aggregated sum of flood occurrence and flooded area of grid-cells located downstream of dams.

Data availability

The H08 model is open source and its source code is available online ( http://h08.nies.go.jp/h08/index.html ). The source code of the CaMa-Flood model can be requested from D.Y. All input data are available through the ISIMIP2b protocol which is freely accessible ( https://www.isimip.org/ ). Detail explanations regarding the coupling procedure, including the new variables introduced in the model and the source file to edit, are available online ( https://zenodo.org/record/3701166 ).

Code availability

Computer code used for analysis and graphic preparation is available online with explanation ( https://zenodo.org/record/3701166 ).

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Acknowledgements

This work was mainly supported by Environment Research and Technology Development Fund (2RF-1802) of the Environmental Restoration and Conservation Agency (grant number JPMEERF20182R02), Japan. It was partially supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant number 16H06291. Y.P. acknowledges the support from the National Science Foundation (CAREER Award, grant number 1752729).

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J.B. carried out the simulation and analysis. J.B., N.H., D.Y., and Y.P. commented on and edited the manuscript.

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Boulange, J., Hanasaki, N., Yamazaki, D. et al. Role of dams in reducing global flood exposure under climate change. Nat Commun 12 , 417 (2021). https://doi.org/10.1038/s41467-020-20704-0

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Lesson Water Resources: Why Do We Build Dams?

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Human-made dams are important in our modern life. Civil engineers and city planners compare the benefits, cost and environmental impacts to determine whether a community could benefit from a dam.

After this lesson, students should be able to:

• Interpret and evaluate data to formulate conclusions.
• Understand the needs for and impacts of dams and reservoirs.
• Describe how the use of technology provides essentials and luxuries for everyday living.

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Where does your water come from? Mountains, rivers, reservoirs? What is a reservoir? A reservoir is a human-made lake created by building a dam. Why do we need dams? When you turn on a faucet at home, where does that water come from? Why is there always water coming out? There is always a supply of water because we hold water in reservoirs. To do this, we must build dams.

For the next several lessons, you are going to be civil engineers working for the company Splash Engineering. Your main client is the government (also known as a "municipality") of Thirsty County. The government of Thirsty County has been receiving complaints from its residents over the last decade. The main problems include:

• Not enough water for people during the summer droughts.
• Farmers have trouble growing food without enough irrigation water.
• During drought periods, the Birdseye River is not deep enough for ships to cross to bring valuable goods to Thirsty County.
• Flash floods ruin houses and stores.
• Air pollution from a nearby coal-fired power plant makes people sick.

The Thirsty County government has hired the Splash Engineering firm (your class) to study the needs of the community and develop a solution that addresses those needs.

Lesson Background and Concepts for Teachers

A dam is built to control water through placement of a blockage of earth, rock and/or concrete across a stream or river. Dams are usually constructed to store water in a reservoir, which is then used for a variety of applications such as irrigation and municipal water supplies. Reservoir water can also be directed to flow through hydraulic turbines, producing electric power for use in homes and industries. Hydroelectric power is considered a renewable source of energy because the reservoir water that is used to generate electricity is continuously replenished. A dam using locks and canals, such as the series of locks on the Panama Canal, enables navigation through a human-made water route that must overcome elevation differences.

The disadvantages of dams include the resulting flooding of large areas of land (destroying flora and fauna), altering the physical characteristics of the river below the dam (also affecting flora and fauna), impeding fish migration, and killing large numbers of fish that pass through hydroelectric turbines. In recent years, engineers and scientists have begun to manage reservoirs and their releases to be less harmful to aquatic and terrestrial wildlife and plants, as well as humans residing below the dam—a method of water resource management called adaptive management.

• How Much Water Do You Use? - Students explore one of the main reasons why dams are built—to satisfy everyday domestic water use. Students track their own water use during one week, and from that data estimate a community's residential water needs from a potential regional dam.

Dams can be useful for a variety of reasons. What are some purposes for which we create dams? (Answers: To supply water for irrigation, municipal water, flood control, hydroelectric power generation, river navigation.) What might be negative effects from a dam? (Answers: Upstream flooding that destroys animals, plants, ecosystems and private property; downstream alteration of terrain, ecosystems, plants and wildlife; impeding fish migration, killing fish that pass through turbines, etc.)

In the case of our imaginary Thirsty County, why should the municipality consider building new dams? (Answers: To provide enough water for people and farmers during the summer, to allow boats to cross Birdseye River year round, to help control flash floods, to produce electricity without air pollution.)

adaptive management: The operation of dams and reservoirs to benefit not only human needs, but also the needs of the aquatic and terrestrial ecosystems impacted by the dam.

dam: A barrier to obstruct the flow of water, especially one made of earth, rock, masonry and/or concrete, built across a stream or river.

engineer: A person who applies her/his understanding of science and mathematics to creating things for the benefit of humanity and our world.

hydroelectric power: Renewable energy generated by water flowing through turbines.

migration: To periodically move from one region or climate to another, as by wildlife such as birds and fish.

municipality: A political unit, such as a county, city, town or village, incorporated for local self-government.

reservoir: An artificial lake where water is collected and stored behind a dam.

turbine: A machine that converts the kinetic energy of falling water (or any moving fluid, including steam, gases or air) into electrical energy by connecting a generator to a rotating shaft that is spun by water pressure pushing blades, buckets or paddles.

Pre-Lesson Assessment

Brainstorming: Ask students to think of all the different ways in which they use water on an everyday basis. Possible answers include drinking, bathing, cooking, swimming, cleaning, etc. Write these answers on the board and then ask the students to tell you where the water comes from for these activities. Students may answer that water comes from rivers, lakes, and streams, in which case you can start a discussion about the need for dams to store water. Be sure to mention that 33% of American citizens get their water from groundwater sources.

Post-Introduction Assessment

Teaming: After you have introduced the hypothetical Thirsty County scenario, divide the class into engineering teams of 2-3 students each, and ask each team to write a short "proposal" response to the municipality of Thirsty County to address the residents' needs. Proposals should comment on the needs of the residents, some possible solutions (at least a Plan A and Plan B), and benefits/problems associated with each plan proposed. For example, students may write a statement that says their team will "address the residents' needs by designing a dam that provides people with water during summer droughts, protects buildings from flash floods and storms, and produces hydropower as a clean energy alternative to coal-fired power plants." This exercise helps students understand their role as civil engineers working for Splash Engineering firm. Emphasize that engineers must propose multiple plans to the County Board and convince the board members that their design is worth spending taxpayer money. Encourage students to address topics such as water-saving appliances, efficient water use in gardens and landscaping, (both water conservation measures) and not building on land that has a high risk of annual flooding.

Lesson Summary Assessment

Pros and Cons: Ask students to think of all the benefits of building a dam (such as water storage, hydroelectricity, flood mitigation, etc.). Create a list of these benefits on the board. Next, ask students to think of some negative effects of dam construction (such as impeding fish migration, damaging flora and fauna, etc.). Next to the list of benefits, create a list of these negative effects. Ask students: "What should engineers do when their designs have both positive and negative impacts on society?" Do students think this is a common dilemma for engineers? (Answer: All engineering projects have positive and negative effects. The main job of engineers is to develop plans to help address problems people have without creating new problems or making other problems worse. If Thirsty County has no money for schools and people are starving in the streets, spending money on a dam might not be the best engineering solution to the water issues Thirsty County faces.)

Lesson Extension Activities

Plan a field trip to a nearby dam to give students a real-world sense of these (often) gigantic engineering structures. If a field trip is not possible, show students a library video on dams or photographs of the Hoover Dam, located on the border between the states of Arizona and Nevada; see a link in the Additional Multimedia Support section.

Show students recent and historic photographs of the well-known Hoover Dam on the US Bureau of Reclamation's Lower Colorado River region website. The photograph gallery provides dam views, power plant, historic views and old post cards. See: http://www.usbr.gov/lc/hooverdam/gallery/picindex.html

As a general introduction to dams, show students a 22-slide overview "virtual tour" of the Shasta Dam in northern California, available at the US Bureau of Reclamation's Mid-Pacific Region page at http://www.usbr.gov/mp/ncao/ and http://www.usbr.gov/mp/ncao/shasta/virtual_tour.pdf

Students learn about the Earth's water cycle, especially about evaporation.

Students are introduced to the basic biology behind Pacific salmon migration and the many engineered Columbia River dam structures that aid in their passage through the river's hydroelectric dams. Students apply what they learn about the salmon life cycle as they think of devices and modifications t...

Students learn about the importance of dams by watching a video that presents historical and current information on dams, as well as descriptions of global water resources and the hydrologic cycle. Students also learn about different types of dams, all designed to resist the forces on dams.

Students learn that dams do not last forever. Similar to other human-made structures, such as roads and bridges, dams require regular maintenance and have a finite lifespan.

Dictionary.com. Lexico Publishing Group, LLC. Accessed July 8, 2009. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Down the Drain: How Much Water Do You Use? 2005. Collaborative Projects, Center for Innovation in Engineering and Science Education (CIESE), Stevens Institute of Technology, Hoboken, NJ. Accessed February 29, 2012. http://www.ciese.org/

United States Society on Dams. Last revised November 14, 2007. USSD. Accessed December 4, 2007. http://www.ussdams.org/

Contributors

Supporting program, acknowledgements.

The contents of this digital library curriculum were developed under grants from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation (GK-12 grant no. 0338326). However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: June 12, 2024

What is a Dam? A dam refers to a structure that is built on rivers and streams. The main purpose of dams is that they facilitate the conservation of water. Water dams are not a modern concept as they have been in existence for many centuries. Historically, dams in India or elsewhere have been very useful in the development of civilizations. Furthermore, a dam is a spectacular feat of infrastructure. These great infrastructural structures have been utilized by civilizations.

Amazingly, it has been in existence since way back in the fourth century B.C.E. This way the civilizations over the years have been able to funnel water via the cities and agricultural fields. Moreover, the use of dams takes place for the prevention of floods , regulating the flow of water in rivers as reservoirs, facilitating irrigation, generation of energy, etc. A dam provides various advantages to a country- social, economic, and environmental.

How are Dams Built ?

A dam is a structure whose building takes place across a river or stream. Holding back water is the main purpose of the dam.

The use of different materials has taken place to build dams over the centuries. In the ancient era, dam builders made use of natural materials like clay or rocks for building a dam. Moreover, nowadays, the use of concrete takes place by modern builders.

For a manmade dam, the creation of artificial lakes known as reservoirs takes place. Experts use these reservoirs to store water for use in housing, industry, and farming. A dam comes in useful for various other activities like boating, swimming, fishing, and other leisure activities.

The first people to build a dam were the ancient Mesopotamians. Jawa Dam is the world’s oldest known dam that is in present-day Jordan. Amazingly, it was built way back in the fourth-century B.C.E.

A dam is a great help to farmers as it can provide them with a steady source of water. This significantly improves the irrigation of crops. Most noteworthy, dams in India and other populous countries are very useful to feed a growing population.

The conservation of water that takes place by a dam can raise some problems. This is because it can cause a major transformation of the habitat in various areas like biological, physical, chemical, or temperature. Due to such changes, the habitat attracts invasive species, thereby becoming hostile for the native aquatic lives.

There can be an increase in the incidence of the disasters like erosion, extinction, landslides, and earthquakes due to a dam. Furthermore, sometimes a major dam can collapse, thereby leading to a major catastrophe. This can lead to hurricanes in earthquakes.

Advantages of Dams

There are some tremendous advantages that come with dams in India and elsewhere. Moreover, this makes it clear that why governments invest so much money into their constructions. Some of the benefits of building a dam are:

• With the assistance of hydroelectric power, the generation of electricity takes place at a steady rate.
• For the preservation of water.
• For irrigation or other activities, the reservoir built behind may also be used.
• The buildup of water within the lake is ensured when required.
• They facilitate storing energy when the release of water takes place for electricity production.
• The electricity generated by the dams  minimizes the production of greenhouse gases.

Negative Impact of Dams

In spite of the several advantages that dams offer, they do pose some challenges to the environment. The below points bring out the negative point of dams :

• Impact on Aquatic Animals:  The flow of streams and rivers is very important for aquatic animals. This is because these animals rely on this flow for the purpose of reproduction.  Most noteworthy, water dams construction can endanger this as it acts as a blockade for aquatic animals.
• Impact on Erosion:  The construction of dams contributes to soil erosion as it eats up most of the surrounding landmass. Furthermore, landslides near the shoreline are often witnessed at a landmass that encompasses reservoirs. This causes significant destruction in the surrounding landmass in a gradual manner.
• Impact on Cost: The construction of dams is a very expensive affair and it also has a huge labour requirement.  Moreover, even if the utilization of a dam takes place for power generation, it would still take several years or decades to recover the investment cost.
• Impact on Relocation:  Relocation can follow the construction of a dam. Furthermore, the need for relocation comes due to the threat of landslides or earthquakes. As such, humans have to relocate their properties and business to avoid potential danger or harm.
• Impact on Water Bodies:   Dams can sometimes block beneficial sediments. Furthermore, aquatic life depends on these sediments. Besides, these sediments play a crucial role in the carbon cycle.
• Impact on Groundwater:  The reservoir can lead to the reduction of groundwater due to the gradually deepening of the river bed. As such, access to groundwater will be denied to the trees and plants in the landmass. Consequently, this leads to the ruining of both marine and terrestrial life forms balance.

How to Make Dams More Environmentally Friendly?

As you have seen, dams can be quite damaging to the environment. However, this does not mean that one cannot remedy it. Below are the measures to make dams more environmentally friendly.

• Making the Dams Fish-Friendly

A dam that is around rivers can disrupt the ecosystem in that water body. Furthermore, the fish passing via the turbines may face death or injury. As such, the experts must find a way to prevent fish from moving through the turbines.

• Minimizing Greenhouse Gases Emissions

Hydropower is not very friendly to environmentally friendly as people think it to be. As such, the dam builders must ensure that the greenhouse gases emissions must be minimized. Moreover, this way, a dam would become safe for the environment in general.

• Utilizing The Currents

Working with the currents is another way of making the dam more environmentally friendly. For this, the engineers must put turbines in streams and rivers in such a manner that they generate electricity without disturbing the water flow. This way the generation of electricity takes place in a natural way.

FAQs For Dams

Question 1: What are the various types of dams on the basis of structure?

Answer 1: On the basis of structure, the dams are of the following types:

• Gravity dam
• Arch-gravity dam
• Barrage dam
• Embankment dam
• Fixed-crest dam
• Earth-fill dam
• Concrete-face rock-fill dam
• Rock-fill embankment dam

Question 2: What are the various functions of dams?

Answer 2 : Below are the various functions of dams :

• Power generation
• Stabilizing water flows
• Water supply
• Land reclamation
• Water diversion
• Flood prevention

Question 3: What are the various considerations that experts must keep in mind when building a dam?

Answer 3: The various considerations that experts must keep in mind when building a dam are as follows:

• Permeability of the surrounding rock or soil
• Water table
• Earthquake faults
• Impact on wildlife, forest, habitations, and river fisheries
• Landslides and slope stability
• Peak flood flows
• Reservoir silting

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Hydroelectric Power: Advantages of Production and Usage

Water use photo gallery, learn about water use through pictures, water use information by topic, surface water information by topic, water science school home.

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Nothing is perfect on Earth, and that includes the production of electricity using flowing water. Hydroelectric-production facilities are indeed not perfect (a dam costs a lot to build and also can have negative effects on the environment and local ecology), but there are a number of advantages of hydroelectric-power production as opposed to fossil-fuel power production.

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The following information references information presented by Itaipu Binacional . Content on this page is taken directly from their website.

Representatives of more than 170 countries reached consensus at the Top World Conference on Sustainable Development, in Johannesburg (2002), and at the 3rd World Forum on Water, in Kyoto (2003): hydroelectric generation is renewable and has certain merits Here are ten reasons leading them to this conclusion.

1. Hydroelectricity is a renewable energy source.

Hydroelectricity uses the energy of running water , without reducing its quantity, to produce electricity. Therefore, all hydroelectric developments, of small or large size, whether run of the river or of accumulated storage, fit the concept of renewable energy.

2. Hydroelectricity makes it feasible to utilize other renewable sources.

Hydroelectric power plants with accumulation reservoirs offer incomparable operational flexibility, since they can immediately respond to fluctuations in the demand for electricity. The flexibility and storage capacity of hydroelectric power plants make them more efficient and economical in supporting the use of intermittent sources of renewable energy, such as solar energy or Aeolian energy.

3. Hydroelectricity promotes guaranteed energy and price stability.

River water is a domestic resource which, contrary to fuel or natural gas, is not subject to market fluctuations. In addition to this, it is the only large renewable source of electricity and its cost-benefit ratio, efficiency, flexibility and reliability assist in optimizing the use of thermal power plants .

4. Hydroelectricity contributes to the storage of drinking water.

Hydroelectric power plant reservoirs collect rainwater, which can then be used for consumption or for irrigation. In storing water, they protect the water tables against depletion and reduce our vulnerability to floods and droughts.

5. Hydroelectricity increases the stability and reliability of electricity systems.

The operation of electricity systems depends on rapid and flexible generation sources to meet peak demands, maintain the system voltage levels, and quickly re-establish supply after a blackout. Energy generated by hydroelectric installations can be injected into the electricity system faster than that of any other energy source. The capacity of hydroelectric systems to reach maximum production from zero in a rapid and foreseeable manner makes them exceptionally appropriate for addressing alterations in the consumption and providing ancillary services to the electricity system, thus maintaining the balance between the electricity supply and demand.

6. Hydroelectricity helps fight climate changes.

The hydroelectric life cycle produces very small amounts of greenhouse gases (GHG). In emitting less GHG than power plants driven by gas, coal or oil, hydroelectricity can help retard global warming. Although only 33% of the available hydroelectric potential has been developed, today hydroelectricity prevents the emission of GHG corresponding to the burning of 4.4 million barrels of petroleum per day worldwide.

7. Hydroelectricity improves the air we breathe.

Hydroelectric power plants don't release pollutants into the air. They very frequently substitute the generation from fossil fuels, thus reducing acid rain and smog. In addition to this, hydroelectric developments don't generate toxic by-products.

8. Hydroelectricity offers a significant contribution to development.

Hydroelectric installations bring electricity, highways, industry and commerce to communities, thus developing the economy, expanding access to health and education, and improving the quality of life. Hydroelectricity is a technology that has been known and proven for more than a century. Its impacts are well understood and manageable through measures for mitigating and compensating the damages. It offers a vast potential and is available where development is most necessary.

9. Hydroelectricity means clean and cheap energy for today and for tomorrow.

With an average lifetime of 50 to 100 years, hydroelectric developments are long-term investments that can benefit various generations. They can be easily upgraded to incorporate more recent technologies and have very low operating and maintenance costs.

10. Hydroelectricity is a fundamental instrument for sustainable development.

Hydroelectric enterprises that are developed and operated in a manner that is economically viable, environmentally sensible and socially responsible represent the best concept of sustainable development. That means, "development that today addresses people's needs without compromising the capacity of future generations for addressing their own needs" (World Commission on the Environment and Development, 1987).

Sources and more information

• Itaipu Binacional

Below are other science topics associated with hydroelectric power water use.

Hydroelectric Power Water Use

Hydroelectric Power: How it Works

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Estimated use of water in the United States in 2015

Estimated use of water in the united states in 2010.

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Home Volumes and Issues Special Issue 14 The environmental and social acce...

The environmental and social acceptability of dams

Dams are an ever more vital tool for addressing our growing water needs and the emergence of new challenges such as sustainable development and climate change. However, these infrastructures are still highly controversial around the world. Citing numerous examples, this paper goes over the main points of debate around dams, and the necessary conditions for securing their acceptability.

Index terms

Keywords: , introduction.

1 Planet Earth needs more and more water and more and more energy, due to growth in population and consumption, especially in developing countries. CO 2 -emitting fossil fuel resources—hydrocarbons such as natural gas, oil and coal—are being consumed at a growing pace, and reserves are inevitably running out, to the detriment of future generations. Post-COP 21, the increased use of renewable energies is a necessity, reinforced by the Paris Agreement. The most economical of all renewable energies is hydroelectricity: it is competitive without costly subsidies, and without posing problems of storage or intermittent supply for electricity network operators. It also offers unique advantages for electricity network operation (frequency and voltage regulation).

2 Demand for fresh water, drinking water and water for irrigation will also greatly increase, with the projected change in climate. Without water, there can be no life on our planet. Fresh water resources are limited and poorly distributed. There are regions where the water supply is the absolute pre-condition for any improvement in standards of living—which are currently too low—and even for the survival of existing communities, as well as the satisfaction of the ever-increasing demand that results from the rapid growth in their population. Such regions cannot do without the contribution that dam-reservoirs make to the management of water resources. We will have to greatly increase our water resources and build new dams. Water storage infrastructures are seen to be indispensable tools both for sustainable development and for adjusting to climate change.

3 And yet the development of dams is controversial, in both the North and South, due to its potential impacts, and new projects often come up against (sometimes vigorous) opposition.

4 The social acceptability of dams is therefore a question of prime importance, and this paper seeks to outline some answers and lines of enquiry, concerning awareness of environmental and democratic issues, with examples of actions in developing countries.

The debate: the benefits and drawbacks of dams

5 The main utilization of the world’s great dams is for food production, by irrigating land that would otherwise be desert. California and Provence are good examples of how dams can transform a territory. Before: drought and desert. After: highly productive regions. The greater part of global demographic growth is happening in arid regions that need water to produce food, or in regions where rainfall is very irregular (monsoon lands), therefore requiring storage methods such as dams’ reservoirs.

6 Hydroelectric energy, with a global output of 2,100 TWh, currently represents 20% of total electricity production and about 7% of all the energy consumed in the world. Hydroelectric dams facilitate adjustable electricity production, by storing huge quantities of water in their reservoirs.

7 Dams hold back river water. By means of turbines, they generate electricity from a renewable source with very few CO 2 emissions. This is hydroelectric energy production—“hydro” to its friends. Unlike wind or solar energy, hydro energy can be stored (in reservoirs) in order to generate electricity when needed, simply by opening the gates. This natural storage of energy is the most competitive form of power storage, making use of PSPSs (Pumped Storage Power Stations), which are crucial for electricity networks and play a key role in integrating other modern renewable energies (solar and wind) that are by nature intermittent.

8 In addition to producing clean carbon-free energy, dams can also, simultaneously, serve other functions: irrigating cultivated land, supplying communities with drinking water, reducing flood flows, replenishing low-water levels, aiding waterway navigation, using reservoirs for tourism and sports, fish-farming, protecting estuaries against tidal backup, and so on.

9 From an energy and climate viewpoint, dams are clearly very positive, and perhaps even represent the most advantageous of all renewable energies, provided that geography and hydrology allow for it.

10 But dams also have downsides: impacts on biodiversity, conflicts of use, risk of breach, and sometimes the displacement of local populations, arousing opposition. And indeed, every dam, hydroelectric or otherwise, blocks watercourses and constitutes an obstacle to the circulation of certain species (fish swimming upstream, notably migratory species such as salmon and eels) and sediments (sand, mud, etc.) which consequently build up and can concentrate pollutants in the reservoir. The absence of new sediments downstream of the dam can cause erosion problems that modify the aquatic environment, undercut riverbanks, or wash away beaches. Dams are therefore a double-sided coin, with a positive side (energy, drinking water, irrigation, flood regulation, river navigation, fight against drought, etc.) and a negative side (ecology, sediments).

Cantoniera dam, on the Tirso, essential to Sardinia’s water supply

photo: ICOLD-CIGB

Dams around the world

11 The map below presents, schematically, the potential hydroelectric power capacity in the various regions of the world. The blue vertical bars represent existing hydro production, and the red bars the economically exploitable capability. It is clear at a glance that North America and Europe have already exploited almost two thirds of their capacity, but that Asia, Latin America, and above all sub-Saharan Africa, still have enormous potential for renewable hydro energy that remains to be developed.

12 In the USA, major dam programs were built during the New Deal: the Tennessee Valley Authority (TVA), the Columbia River Basin, etc. They played a fundamental role in the development of the country’s interior. Prior to the TVA, the Tennessee valley was still under-developed, with a population marked by high rates of illiteracy and ravaged by malaria. Hydro is the largest source of clean electricity in America, accounting for 51% of all renewable energy production in the USA. However, environmental concerns are growing, and it is becoming very difficult to create new facilities: very little hydroelectricity has been brought on stream in the USA over the last 20 years. Although President Obama announced his intention to relaunch the program, the construction of new hydroelectric dams in the USA is currently limited for several reasons: the best sites are already developed, clashes with protesters over environmental issues are increasing, and restrictive regulation is scaring away investors who might be interested in hydro, as the licensing process becomes ever longer and more difficult. Increases in hydroelectric capacity are therefore limited mainly to reinforcing and improving existing structures.

13 In Canada, Hydro-Quebec has developed large dams in the North, in James Bay, a highly profitable source of electricity, which is partly exported to neighboring regions and the USA. In China, the country with the world’s fastest growing economy, mounting energy needs are driving an ambitious program: more than 50 major dams were planned in the 12 th  five-year plan (2011-2015) to achieve the 15% renewable energy target in China—the world’s leading greenhouse gas emitter—by 2020.

14 China has, by far, the largest hydroelectric potential in the world.

15 Since July 2012, the famous Three Gorges Dam has reached full power at 22,500 MW, the current world record (a capacity equivalent to more than a dozen nuclear reactors or some thirty coal-fired power stations). More than 1.2 million people were resettled, and more than a hundred towns and villages disappeared under the waters of the Yangtze. It is worth remembering that the main motivation for building the dam was not electricity production but rather to combat the violent floods to which the Yangtze was prone, which regularly killed thousands of victims (100,000 dead in 1911, 145,000 dead in 1935, 33,000 dead in 1954) and left hundreds of thousands of homes destroyed and families with nowhere to live.

16 The new Xiluodu Dam, a 278-meter-high arch dam, has been linked to a 13,860 MW hydroelectric power plant since 2014, making it the second largest hydro dam in China after the Three Gorges Dam (and the third in the world after Itaipu, in Brazil-Paraguay). 180,000 people were displaced.

17 In Egypt, the great Aswan Dam on the Upper Nile, built by the Soviets in the 1960s without any environmental impact study, has unfortunately had negative consequences, holding back the sediments of the Nile that build up and clog the reservoir, and are sorely missed in their role of providing fertilizing silt for the floodplains of the Nile. Since its construction, however, Egypt has avoided the famines that had afflicted the country regularly for centuries.

18 In sub-Saharan Africa, where the rate of electrification remains very low despite an explosion in demographic growth, there is an enormous hydroelectric potential to be developed. One need only look at the dams of Manantali (Mali, Senegal, Mauritania), Garafiri in Guinea, “Renaissance” in Ethiopia, on the Upper Nile, Ruzizi 3, the Zambezi...

19 The Grand Inga Project is worth particular attention: on the Congo river, downstream from Kinshasa, it will generate almost 40,000 MW of background hydro power throughout the year (almost twice as much as the Three Gorges) thanks to a exceptional site with a “zigzag” shaped head of 80 meters and a huge flow rate in “run-of-river” configuration, with no large backed-up reservoir, thus limiting the environmental impact, and making the cost per kWh produced and delivered extremely competitive. The potential capacity far exceeds the needs of the DRC, but South Africa is interested in the project, which would enable it to reduce its dependency on coal; moreover, part of the vast energy of the Grand Inga Project is to be devoted to an “Energy for Africa” program. There are many other sites that could be developed in Africa, and projects that could be financed within a renovated institutional framework that allows investors to participate in public-private partnerships.

A recent example: the Nam Theun Dam

20 The Nam Theun project, a dam in Laos that supplies power to Thailand, strives to be the model of a successful project: creating local wealth while preserving natural resources, providing access to water, and regulating the course of the river while reducing greenhouse gas emissions. An exemplary program has been put in place to resettle local communities.

21 The sustainable development of dams (complying with the criteria defined by the World Bank and with the CIGB guidelines) is indispensable for access to energy in developing countries. It resolves problems of drought and river regulation, as well as access to energy, without using fossil fuels, and is a far more regular and reliable renewable energy source than wind. The only requirement is that we define ground rules that are valid in the long term and which preserve the environment, by means of detailed and credible impact studies.

A French example of acceptability ultimately achieved: the Tignes Dam

22 France’s highest dam, the 180-meter high Tignes Dam , was for a long time Europe’s highest dam. Situated in the Chevril valley on the Isère river, it is a beautiful, curved arch dam.

23 But this large-scale project had a very bumpy ride... When it was launched, in 1948, the project came up against strong resistance from the local population. The inhabitants took the case to court, seeking to obtain the annulment of the decrees declaring the dam project to be in the public interest, and contesting the offered amount of compensation for expropriation. The building of the dam and the creation of the reservoir, the artificial Lake Chevril, submerged the village of Tignes and five hamlets. At the time, there were even some attempts to sabotage the construction. The lake eventually engulfed the village, its church, and its cemetery. Four hundred people were displaced when the dam was built, and rehoused in the new modern village of Les Boisses built a few kilometers from the historic Tignes (and which is now a well-known ski resort).

24 Despite the fierce local opposition at the time, the dam addressed a real national need: after the Second World War, there was no choice but to build new electricity production infrastructure in order to meet the large rise in electricity demand.

25 70 years on, Tignes is well-integrated into its environment, and a successful example of both social acceptability and regional development.

The difficulty of gaining acceptance for dams today

26 In France today, would it be possible to build a dam project such as Tignes, engulfing villages and hamlets? It seems unlikely, given the strong emotional and even violent opposition to small-scale dam projects, such as the simple irrigation reservoir at Sivens in the Tarn valley, which regrettably led to violent clashes in October 2014 between anti-dam protesters and the police, and in which an environmental activist was killed.

27 It would be fair to say that dams embody a contradiction: globally, they have many advantages, but locally — especially for local populations — the advantages are outweighed by drawbacks: flooded land leading to dispossession and discontent, thus requiring assessment and compensation.

28 More broadly, a structural opposition emerges between the public interest, which is situated at a wider territorial level—perhaps national or even planetary—and local interests, rooted in the areas directly concerned by each dam and reservoir project.

29 Yet acceptance must be found at every level, global and local. In the past, and particularly in developing countries, there were cases of so-called “white elephant” dam projects that paid no regard whatsoever to local realities. These dams—often associated with mining operations—contributed to some extent to industrial development, thanks to the electricity generated, but were of no benefit to the populations affected by their construction. In some cases, local communities were still without electricity 20 years after the dam was built. This local level is now more important than it used to be, with less central government control, and more local power devolved to “civil society”.

30 In the case of the monumental Three Gorges Dam, more than a third of the total budget is estimated to have been allocated to operations designed to compensate affected populations.

31 Dams have a critical geographical component: they can only be located in geographically favorable sites, with a strong head of water: a good gradient and an adequate flow of water in the river. Such sites are often inhabited. It is important to bring local populations in on the project, in all of its aspects, not least its cultural and sociological components.

32 Today, potential hydro sites (typically in mountain valleys) are often a long way from the centers of consumption; the electricity therefore has to be transported over large distances, or even between countries, such as Laos and Thailand for the Nam Theun project. Good cooperation is required between countries, as well as stability to limit the risk taken by investors. Very large-scale projects are the most complex of all. When it comes to acceptability, in certain cases “small is beautiful”.

33 At the global level, non-governmental organizations (NGOs) opposed dams in the 1990s, demanding the abandonment of funding for large dam projects, sparking controversy. The World Bank, previously one of the main backers of dam projects in the third world, had halted almost all funding during the 1990s, preferring to focus on telecommunications. In May 1998, in response to the controversy over large dams, it set up—jointly with the International Union for the Conservation of Nature—the “World Commission on Dams” (WCD), which published its report in November 2000. The report was given a lukewarm reception.

34 While there was general agreement on the five core values and the seven strategic priorities set out by the WCD, the dam experts representing ICOLD expressed strong reservations about the policy principles and guidelines proposed in the report. The anti-dam NGOs, by contrast, welcomed the WCD report with joy and treated it as gospel, and beyond dispute. Time has delivered its verdict: according to professor John Briscoe  1 from the Harvard School of Engineering,“… [the WCD] was over since it published its final report. At that time, none of the large dam-building nations supported it and nobody used it since then to build a dam.”

The Trängslet Dam in Sweden

photo: ICOLD

35 Given these facts, and the growing influence of emerging countries at the World Bank, the latter revised its stance on dams. This radical change took the form of a New Water Sector Strategy, adopted in 2003. At the same time, the Bank’s departments were working on guidelines for better addressing the environmental and social impact of large dams. These enabled the financing of hydro projects in developing countries to resume.

36 Recently, Rachel Kyte, speaking as the World Bank’s Vice President and Special Envoy for Climate Change at the Global Water Forum, went so far as to assert that “as we move toward green growth, large-scale water infrastructure has an essential role to play”. And the World Bank has begun to fund feasibility studies on large dams again, on the condition that its environment guidelines are followed.

37 Dam builders therefore had to expand their criteria for assessing projects. In addition to the three classic criteria of technical, economic and financial feasibility, dam projects must now meet a fourth, very demanding, criterion: that of their acceptance by the public and by elected representatives. This criterion has become as important as the safety criterion.

38 Beyond the environmental question in the strictest sense, there is a social aspect, one that touches on a broader meaning of the word “environment”: people, their land, their habitat, their economies and traditions. The impact of dams and reservoirs on this environment is inevitable and undeniable; land is flooded, people are resettled, the continuity of aquatic life along a river is interrupted, and the water flow is modified and often reduced by catchments. Thus, dam engineers find themselves confronted with the basic problems inherent in transforming the natural world into a human environment. In our never-ending quest to provide a growing number of people with a better life, the need to develop natural resources, including water, means that the natural environment cannot be preserved completely unchanged. But great care must be taken to protect the environment from all avoidable harm or interference. We must cooperate conscientiously with nature’s inherent fragility as well as its dynamism without ever overtaxing its powers of regeneration, and its ability to adapt to a new but ecologically equivalent equilibrium. And we must ensure that the people directly affected by a dam project are better off than before.

39 Today, the process of building a dam is very different from what it was in the 1960s, when the engineer was in sole command. The economist and the financier took their place on the project team during the 1970s and 80s. More recently, since the first UN Environment Conference (Stockholm, 1972), the enormous increase in human knowledge, particularly in the field of environmental science, means that a whole team of specialists is needed to access and utilize that knowledge for any water resource development project. This multidisciplinary approach is better able to encompass the full complexity of this type of project.

40 The larger the project, the greater the effects on the natural and social environment, and the wider the scope of the multidisciplinary studies that will be needed. Large-scale dams require integrated planning for an entire river basin before any construction projects are implemented. Where river basins are part of more than one country, such planning presupposes international cooperation.

41 Involuntary resettlement must be handled with special care, managerial skill and political sensitivity based on comprehensive social research, and sound planning for implementation. The associated costs must be included in the comparative economic analyses of alternative projects, but should be managed independently to make sure that the affected population will be properly compensated. For the communities involved, resettlement must result in a clear improvement of their living standards, because the people directly affected by a project should always be the first to benefit, instead of suffering for the benefit of others.

42 Special care must be taken for vulnerable ethnic groups. Hence, the organization of the overall decision-making process, incorporating the technical design as a sub-process, should involve all relevant interest groups from the initial stages of project design, even if the existing legislation does not (yet) demand it.

43 Such concerted action requires continuous, comprehensive and objective information on the project to be provided to governmental authorities, the media, local action committees and NGOs, and—above all—to the people directly or indirectly affected, and their representatives. In this transfer of information from planners to public, dam engineers must contribute, through their professional expertise, to a clear understanding and dispassionate discussion based on facts, and not on emotive ideas about the positive and negative aspects of a project and its possible alternatives. Dam promoters must act as mediators and educators in order to win acceptance.

44 Are dams a benefit, a valuable water and renewable energy resource? Or a necessary evil?

45 There is a growing awareness among certain NGOs specializing in development that well designed, well-built dams can be effective instruments of sustainable development.

46 Conversely, in “democratic” countries, it is becoming increasingly difficult to implement large-scale projects (power lines, high-speed rail lines, dams… even wind projects). These meet with strong opposition, even giving rise to defense committees.

47 So many questions, for which there is no single answer — and no one-size-fits-all model. When it comes to the demand for energy in the field, multiple factors — technical, financial, institutional and psychological — come into play. Social acceptability is imperative. We must remain concrete and pragmatic: a multitude of micro-decisions is involved. Although the sheer multiplicity of actors can make partnerships complicated, it is important that these are developed, thus combining and integrating the know-how and value of the contributors — public sector, private sector and market forces — and setting up local companies to run and maintain the installations and market their services over the long term.

48 We believe that to be effective in meeting the huge energy, environment and sustainable development challenges that lie ahead, the cooperation of all of the actors will be needed for a long time to come, in particular that of the users and communities concerned, through a continuous effort of learning and education. The answer surely lies in successful implementations in the field, close to local populations, in a way that is innovative, sustainable and reproducible, creating a virtuous circle of progress.

49 Henri Boyé, Honorary Engineer-General (Corps of Bridges, Waters and Forests) has worked in France’s energy sector, notably on dam inspections, and internationally, as Director for Africa and subsequently Executive Director in Morocco for Electricité de France (EdF), and as an expert in renewable energies. He has served as Energy and Climate Coordinator for CGEDD (Conseil Général de l’Environnement et du Développement Durable). He currently works as an energy consultant, advising the Prime Minister’s office in Kinshasa, DRC.

50 Michel de Vivo, Engineer, is Secretary General of CIGB-ICOLD (Commission Internationale des Grands Barrages/International Commission on Large Dams). He has served as Governor of the World Water Council. In the course of his career, he has managed several dam reconstruction projects in Africa and the Middle East.

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Electronic reference

Henri Boyé and Michel de Vivo , “The environmental and social acceptability of dams” ,  Field Actions Science Reports [Online], Special Issue 14 | 2016, Online since 15 April 2016 , connection on 18 September 2024 . URL : http://journals.openedition.org/factsreports/4055

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Hydropower Dams and Their Environmental Impacts Essay

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Considering all the harmful environmental effects that hydropower dams have, many countries in the world are now fighting the construction and maintenance of large dams by prohibiting their funding. Even though dams are supposed to bring particular economic benefits, many people argue that they do “more economic harm than good” (“Social, environmental impacts of dams can be reduced” 10).

To start with, dams are expected to assist in mitigating floods, generating electricity, and supplying water for various industries and agriculture (Rosenberg, Mccully, and Pringle 747). Finally, the least they do is improve the navigation of rivers. However, the practice shows that all of those advantages are arguable and can hardly compensate for the harm that dams, especially the large ones, are fraught with.

First of all, any hydrological alteration disrupts the natural river flows, and as Rosenberg, Mccully, and Pringle state in their article, dams are “a major cause of these disruptions” (747). For example, dams usually become the reason for the loss of river deltas and dewatering of rivers and contribute to water pollution. When there are too many dams on the same river, its waters can even stop reaching the sea, although they are supposed to. As Rosenberg, Mccully, and Pringle write, the Colorado Rivers rarely discharge any freshwater to the sea (749).

Secondly, because of water stored in reservoirs, the worldwide sea level has significantly reduced (Rosenberg, Mccully and Pringle 747). Since the middle of the twentieth century, the approximate volume of water impounded in reservoirs has reached the point of 10,000 cubic kilometers, which equals the amount of water in all rivers around the world (Rosenberg, Mccully and Pringle 747). Additionally, dams and reservoirs contribute to greenhouse gas emissions.

Another significant harm that large dams cause is that regarding river inhabitants. Dams usually become the reason for habitat fragmentation and changes; they block the migration of fish, hinder spawning, and so forth. As proof, after four dams were constructed on the Snake River, people faced a significant deterioration in salmon fishing (Rundle 138).

To conclude, the construction, funding, and maintenance of hydropower dams have numerous adverse consequences, including the disruption of the natural river flows, decrease in the water level in the seas, the contribution to the greenhouse emissions, etc. The possible advantages that those constructions can bring can not compensate for all the negative consequences, which is why the use of large hydropower dams should be terminated.

Works Cited

Rosenberg, David M., Patrick Mccully and Catherine M. Pringle. “Global-Scale Environmental Effects of Hydrological Alterations: Introduction.” BioScience 50.9 (2000): 746-751. Print.

Rundle, Simon D. “Threats to the Running Water Ecosystems of the World.” Environmental Conversations 29.2 (2002): 134-153. Print.

“Social, environmental impacts of dams can be reduced: IIED.” Ecos 195 (2014): 10-11. Print.

Burton, Tony, David Sharpe, Nick Jenkins and Ervin Bossanyi. Wind Energy Handbook , West Sussex, England: John Wiley & Sons, 2001. Print.

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17 Biggest Advantages and Disadvantages of Dams

We use dams to impede or stop the flow of water along a river. Although this engineering structure gets commonly associated with the production of hydroelectric energy, we also use them for a variety of different purposes. When a river gets dammed, it creates an artificial lake behind it that can be used for drinking water, recreational purposes, and irrigation.

The first dams that humans created were considered gravity dams. They were made of masonry or concrete that could resist the water load because of their weight. The ancient Egyptians are thought to have built the first one, and it was called Sadd el-Kafara. That name translates to “Dam of the Pagans” in Arabic. Archaeologists believe that the structure was 37 feet tall and almost 350 feet wide at its crest. Over 100,000 tons of stone and gravel were used to build the structure, but it failed after a few years because of overflows.

Several advantages and disadvantages of dams are worth reviewing when we look at the immediate and long-term impacts of this technology.

List of the Advantages of Dams

1. Dams provide us with a source of clean energy. Hydroelectricity is responsible for 19% of the world’s energy supply, offering over 3000 terawatts each year. We can produce power from dams because of the kinetic energy of the water movements as it causes turbines to spin. That’s what allows us to generate electricity that is clean and renewable. Once the dam gets entirely constructed, we no longer have a dependence on fossil fuels to be responsible for the energy we need to maintain a modern lifestyle.

The United States is one of the largest producers of hydroelectricity in the world today, even with the reduction of operational facilities. Americans generate over 103,000 megawatts of renewable electricity with this resource, with only Canada currently creating more power in this way.

2. Dams help us to retain our water supply. When we take an opportunity to dam a river, then the water will pool to form a reservoir behind the structure. This outcome allows the population centers in that region to collect fresh water during periods of heavy precipitation for use during a dry spell or drought. We also use this engineering marvel to control floodwaters or to supply a fixed amount of fluid to the surrounding areas for agricultural irrigation.

That means a dam can provide a buffer to an entire region against extreme weather events or irregular precipitation patterns.

3. This technology provides us with critical recreational opportunities. Dams can provide us with a wide range of economic, environmental, and social benefits. Numerous reservoirs around the United States offer opportunities to go camping, boating, and waterskiing. It gives regions that generally wouldn’t have water access a place to have a boat launch that supports commercial fishing activities. These destinations can be the perfect place to have a picnic, go hiking, and spend time with your family.

4. A well-constructed dam provides several flood-control benefits. Dams help to prevent property loss while reducing the risk to human life from annual flooding events. These structures can impound the floodwaters into the reservoir behind the dam, allowing us to release them under control or to store it for future use. We can divert excessive precipitation toward municipalities for fresh drinking water, create more irrigation opportunities, and meet a variety of energy-related needs.

The Nile River is famous for its unpredictable annual flow throughout history. As climate change continues to progress, the patterns of El Nino and La Nina in the Pacific Ocean will continue to increase. That means we will have more cycles of excessive precipitation and drought, and dams can help us to regulate this issue.

5. Dams give us a way to irrigate croplands that may not receive enough moisture. About 10% of the croplands in the United States are currently irrigated using water that is stored in reservoirs behind a dam. Tens of thousands of jobs are directly tied to crop production and other agricultural activities that happen because of this benefit. Our food distribution networks remain active and consistent because of this advantage, and it allows us to do more with our growing efforts than if we relied on seasonal precipitation patterns alone.

6. A dam can provide a stable system of navigation. We can use dams on rivers to provide a stable system of inland water transportation. The navigable waterways of the United States, like those found on the Mississippi River, can be challenging for some boats to use because of varying water levels. Installing a system of locks with this technology creates a safe place for us to transport goods and a variety of additional benefits.

In some situations, dams can even provide enhanced environmental protection. This technology has the capability of delivering hazardous materials retention or reducing the influence of sedimentation on vulnerable rivers.

7. Reservoirs can serve as a source of drinking water. Because the water stored behind a dam in a reservoir is fresh, we can use it as a source of drinking water for nearby towns and cities. It is not unusual for communities in the United States to obtain their entire supply from streams or rivers that are close. We can use large canals, pipes, and other methods of transportation to ensure that every home has access to safe and clean drinking water.

List of the Disadvantages of Dams

1. Dams can displace a significant number of people. An estimated 500 million people have been displaced by dams in the last two centuries because of the reservoirs that form behind each structure. As the surrounding dry areas get flooded, we no longer have the option to use land that was previously accessible for a variety of purposes. That means local agricultural activities go through a disruption process, even though the eventual increase in available water supports more irrigation.

2. Reservoirs behind a dam can lead to higher greenhouse gas emissions. When vegetation gets engulfed in water, then the plants will eventually die. When this outcome occurs, the dead organic material releases methane that ultimately makes its way into the atmosphere. The increase in the production of greenhouse gases is significant because methane is up to 20 times more potent as a reflector than carbon dioxide.

The use of a dam in certain areas can also contribute to the loss of forests. When we lose a significant number of trees simultaneously, then there is a corresponding uptake of carbon dioxide that occurs because there are fewer photosynthesis processes happening each day.

3. This technology disrupts local ecosystems. Dams create a flooding issue behind the structure as a way to form a reservoir. Not only does this disrupt human activities, but it also destroys the existing wildlife habitats that exist. This issue can disrupt entire ecosystems, which can have an adverse effect on a whole regional biome. Marine life that relies on an unobstructed flow of a river, such as migratory fish, can be adversely affected by the decision to dam the water.

4. Some river sediment is beneficial. Dams can have a profound impact on the overall aquatic ecosystem of a region. The transformation upstream creates a lack of settlement that moves down the waterway to support the entire marine habitat. It can also cause changes in temperature, chemical composition, and shoreline stability. Many reservoirs also host invasive species, such as algae or snails, that undermine the natural communities of the plants and animals that lived on the river before.

The riverbeds that are downstream from a dam can erode by several yards within the first decade of operations. This damage can extend for hundreds of miles downstream afterward.

5. Dams create a flooding risk if they experience a failure. We might use dams to provide us with a form of flood control, but the failure of this structure can have devastating consequences for downstream communities. The Vajont Dam Failed in 1963, only 4 years after its construction was finalized just outside of Venice, Italy. A landslide during the initial filling triggered a tsunami in the reservoir, causing over 50,000,000 cubic meters of floodwater that impacted nearby towns and villages. Some reports say that the wave was over 820 feet high.

Almost 2,000 people died in this disaster, and it was all because the dam was located in a geologically unstable area. When the Banqiao Reservoir Dam failed in 1975 in China, it caused an estimated 171,000 deaths.

6. Dams can have an adverse impact on the groundwater table. When riverbeds experience deepening, then this problem creates a lower groundwater table along the river. That means it is more challenging for plant roots to reach what is required for survival. Homeowners in the vicinity must also dig deeper wells to draw water for their households. This issue can even change the mineral content and salts found in the fluid, creating damage to soil structures along the way.

7. The construction of a dam is a costly investment. A large dam is defined as a structure that is higher than 15 meters. This definition means there are more than 57,000 structures around the world. Major dams are over 150 meters tall, and there are over 300 of these. China has the most, with over 23,000 operational facilities. The United States is in second, but far behind at 9,200. The cost of a large dam today can be over $20 billion, and it may take between 7 to 10 years to complete its construction. Those are resources that many communities could put to better use.

8. Dams can block water progression to different states, provinces, and countries. When a dam gets built at or near a border between two states, provinces, or countries, then it might also block the progress of the water in one of those areas. That means the supply from the same river in the neighboring country is no longer under their direct control. This disadvantage can result in severe issues between neighbors, creating a constant source of conflict that can sometimes even lead to war.

9. It can make the water too shallow for navigation. Dams try to avoid environmental impacts by releasing water downstream and creating marine life channels that allow for upstream movement. Although this approach is imperfect, the updates to this engineering process have had some benefits. What doesn’t get solved through this process is the depth of water that might be available downstream. The Colorado River is an excellent example of this issue because the waterway doesn’t make it to its outlet most years because of all the damming activity that occurs.

If the waters are too shallow to use in a river, then there is no way to use it for transportation benefits. This issue also changes the settlement profile so that marches and wetlands no longer receive the healthy supports from the river that they need.

10. Reservoirs can be challenging to maintain. When drought is a significant issue for a community, then a reservoir that’s behind a dam can be a vital resource. Maintaining this new body of water comes with a set of its own challenges because evaporation can happen during dry times and result in an increase in environmental problems. There also tends to be a significant buildup of organic matter in the sediment with this disadvantage, resulting in potentially carcinogenic trihalomethanes when the water gets chlorinated for drinking purposes.

The Klamath River Has worked under the influence of four dams for almost 60 years. Those structures generate an average of 82 megawatts of power annually. That energy might be renewable, but it is not free of environmental consequences. These structures took a dynamic ecosystem and replaced it with a wretched impostor of itself. Even the dams’ owner decided that the cost of maintaining the structures it was no longer worth it, and so they are coming down.

The Reventazon Dam in Costa Rica tells a very different story. Engineers over the past 6 years have steadily corralled the river so that the facility can generate 305 megawatts of electricity annually. This project is the largest of its kind in Central America, and it almost guarantees that the country’s electrical grid will be nearly 100% renewable energy.

When we examine the advantages and disadvantages of dams, it is essential to remember that both perspectives make legitimate claims to be doing what is best for the environment. These structures might be coming down in the United States, but they are going up all over the rest of the world. That means this technology is going to be in the past for some populations, but it will also be the future for others.

Geography Notes

Essay on dams | india | geology.

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Here is an essay on ‘Dams’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Dams’ especially written for school and college students.

Essay on Dams  

Essay # 1. introduction to dams :.

A dam may be defined as a solid barrier constructed at a suitable location across a river valley with a view of impounding water flowing through that river.

Dams are constructed for achieving any one or more of the following objectives:

(i) Generation of hydropower energy;

(ii) Providing water for irrigation facilities;

(iii) Providing water supply for domestic consumption and industrial uses;

(iv) Fighting droughts and controlling of floods;

(v) Providing navigational facilities;

Additional benefits coming from dams are development of fisheries and recreation facilities in the reservoirs created by them and also the overall greenery effect all along the reservoirs.

In a country like India where rainfall is erratic and depends considerably on the vagaries of seasonal winds – the monsoons, importance of dams can hardly be overemphasized. Hundreds of thousands kilometer long irrigational canals being fed by reservoirs created by around four thousand minor and major dams spread throughout the country have been responsible, to a great extent, for making India self-sufficient in food production.

ADVERTISEMENTS: (adsbygoogle = window.adsbygoogle || []).push({}); Essay # 2. Types of Dams :

Although no two dams are exact copy of each other, it has been a practice to classify these structures on the basis of:

(a) Design of construction, whether the load of the body of the dam is transmitted on the foundations or to the abutment rocks; such as gravity dams, arch dams, buttress dams etc.

(b) Material of construction, such as concrete, rockfill or earthfill dams;

(c) Size of the construction, such as small dams and large dams;

The well-known main types of dams are the gravity dams, the arch dams and the embankment dams.

International Congress on large dams defines a large dam as one which has a height of more than 15 m from the lowest portion of the general foundation area to the crest.

Dams with heights falling between 10-15 m but satisfying the following conditions are also classed among the large dams:

(i) Length of the crest of the dam is greater than 500 m;

(ii) Capacity of the reservoir is not less than 1 million cubic meters;

(iii) Maximum flood discharge not to be less than 2000 cubic meters/second.

In India, there were about 4000 large dams meeting the above definitions at the end of twentieth century. The greatest number of large dams are in Maharashtra (1508) followed by Madhya Pradesh (752), Gujarat (365), Karnataka (213), Orissa (149) Rajasthan (128) and Uttar Pradesh (109). Punjab had only two dams whereas Haryana, Mizoram, Nagaland and Sikkim did not have a single large dam till then.

The tallest dam (the Bhakra Dam) with a height of 226 m and length at crest of 518 m is located in Himachal Pradesh and the longest dam (the Hirakud dam) having a height of 59 m and length of about 5 km (4800 m) is built across Mahanadi in Orissa. The Bhakra Dam is a gravity dam and the Hirakud Dam an embankment dam. The only arch dam, the ldduki Dam is located in Kerala.

The salient features of principle types of dams are as follows:

a. Gravity Dams :

A gravity dam is a solid masonry or concrete structure, generally of a triangular profile, which is so designed that it can safely stand against a pre-calculated volume of water by virtue of its weight. All the forces arising in such a dam – as due to the thrust of the impounded water and the massive weight of the dam material – are assumed to be directly transmitted on to the foundation rocks. Hence the strength of the foundation rocks is the most critical factor in their design.

A gravity dam, when properly designed and carefully constructed, is considered among the safest types.

Many derived types of gravity dams have also been constructed with advantage. The Buttress Dam is such a type in which a thin concrete slab is supported from the downstream side by buttresses thereby saving considerable construction material. The upstream face in a gravity dam may be vertical or inclined.

Similarly, the axis of the dam may be straight or a curvature may be induced in the design of the dam. The buttresses in such dams are narrow, heavily loaded structures which take most of the load from the dam and transmit the same to isolated foundations under them. Hence rocks must be exceptionally strong under the buttresses.

b. Arch Dams :

An Arch Dam, as the name implies, is an arch-shaped solid structure mostly of concrete, which is designed in such a way that a major part of the thrust forces acting on the dam are transmitted mainly by the arch action, (and also cantilever action at the base) on to the abutment rocks, that is, rocks forming the left and right sides of the stream valley. Hence, such dams can be built even on those sites where the foundation rocks may not be sufficiently strong.

Two main types of Arch Dams are:

i. The constant radius Arch Dam, in which the radius of curvature throughout the structure is constant and upstream face, is vertical.

ii. The variable radius dams, in which curvatures are different on the upstream and downstream sides. An arch dam having a curvature both in horizontal and vertical alignment is often called a cupola dam.

Arch dams are better suited for narrow valleys with strong and uniformly sloping walls or abutments. In ideal situation, they offer many advantages over the other types of dams. Arch dams are quite thin walled compared to gravity dams and hence lighter in weight.

Sometimes the designers mix the better points of both the gravity and arch dams and prefer to design a mixed arched-gravity-dam. A combination of series of arch dams called the Multiple Arch Dams is sometimes applied with advantage when the valley is too wide for a single arch or gravity dam.

The ldduki dam in Kerala (India) is an important Arch Dam of our country.

c. Embankment Dams :

These include a variety of non-rigid structures which are built over wide valleys with varying foundation characteristics from easily available materials such as earth and rock fragments. These are generally of trapezoidal shape. In design they may be made up of a single type of material (such as earth fill or rock fill) or a combination of more than one material.

Their main advantage over other types of dams is that they can be constructed even on weak foundations such as unconsolidated Weak River or glacial deposits. An embankment dam is constructed as a homogeneous construction but very commonly with a properly compacted core of an impervious material such as clay. Concrete cores with proper cover are also provided in many embankment dams.

Depending upon the type of material used, the embankment dams may be an earth fill dam or rock fill dam or mixed-type embankment. The clay core wall is made up of simple dug up and cleared, thoroughly compacted, puddled clay or rolled clay. It is followed by two or more layers of proactive transitional layers before the actual “fill” starts. The Hirakud dam in Orissa is one of the longest embankment dams of our country.

Essay # 3. Geotechnical Considerations for Designing and Constructing Dams :

Whereas a decision regarding placing a dam across a particular river and creating a reservoir or basin is always based on socio-economic considerations, its design and construction are essentially civil engineering activities involving important geotechnical parameters.

Detailed answers to following main questions have to be obtained:

(i) The exact location where the dam should be placed against the river along its longitudinal profile;

(ii) The type of dam that will be most suitable for that particular site;

(iii) The availability, cost and quality of the materials required for the construction of the dam.

Obviously, answers to above questions would involve very systematic and thorough geological investigations along the river valley in general and in some preliminarily selected areas in particular. The problem may be divided, for discussion purpose, into two categories – geotechnical considerations for dam sites and for reservoir sites. The two are, however, intimately interlinked and both the dam site and the reservoir area must be geologically suitable for a safe, stable and economical project.

Essay # 4. Selection of Sites for Dams :

The Objectives :

The main object of placing a dam across a river is to impound its water behind the dam.

Naturally, this would require that:

(a) Topographically, a place which is most suitable for the purpose is selected. Ideally, it would be a narrow gorge or a small valley with enough catchment areas available behind so that when a dam is placed there it would easily store a calculated volume of water in the reservoir created upstream.

This should be possible without involving significant uprooting of population, loss of cultivable land due to submergence or loss of existing construction. Also, strategically the location of a dam, especially a major project, is so decided as to cause minimum damage to the public in case of its destruction or failure.

(b) Technically, the site should be as sound as possible – strong, impermeable and stable. Strong rocks at the site make the job of the designer much easy – he can evolve best deigns. Impermeable sites ensure better storage inventories.

Stability with reference to seismic shocks and slope failures around the dam, especially upstream, are a great relief to the public in general and the engineer in particular. The slips, slides, and slope failures around and under the dam and susceptibility to shocks during an earthquake could prove highly hazardous.

(c) Constructionally, the site should not be far off from deposits of materials which would be required for its construction. All types of major dams require millions of cubic meters of natural materials—earth, sand, gravel and rock – for their construction. Their non-availability in the adjoining areas would make the project cost too high, may be even unfeasible.

(d) Economically, the benefits arising out of a dam placed at a particular site should be realistic and justified in terms of land irrigated or power generated or floods averted or water stored. Dams are invariably costly structures and cannot be placed anywhere and everywhere without proper analysis of cost-benefit aspects.

(e) Environmentally, the site where a dam is proposed to be placed and a reservoir created, should not involve ecological disorder, especially in the life cycles of animals and vegetation and man. The fish culture in the stream is the first sector to suffer a major shock due to construction of a dam. Its destruction may cause indirect effects on the population. These effects require as thorough analysis as for other objects. The dam and the associated reservoir should become an acceptable element of the ecological set up of the area.

Geological Characters for Investigation :

For achieving the above objects, thorough and systematic investigations of following geological characters of the areas in general and of the preliminarily selected site in particular would have to be carried out.

(1) Geology of the Area :

Preliminary geological surveys of the entire catchment area followed by detailed geological mapping of the reservoir area have to be conducted.

These should reveal:

(i) Main topographic features,

(ii) Natural drainage patterns,

(iii) General characters and structures of rock formations such as their stratification, folding and faulting and igneous intrusions, and

(iv) The trend and rate of weathering and erosion in the area.

Such a study when interpreted properly would rule out some areas for the dam placement and help in identifying the locations that are most suitable topographically and economically, where further detailed geological investigations could be carried out. For obtaining the above information, conventional geological and geophysical surveys need to be conducted.

(2) Geology of the Site :

(a) Lithology:

The single most important feature that must be known thoroughly at the site and all around and below the valley up to a reasonable depth is the Lithology, i.e. types of the rocks that make the area. Surface and subsurface studies using the conventional and latest techniques of geological and geophysical investigations are carried out.

Such studies would reveal the type, the composition and textures of the rocks exposed along the valley floor, in the walls and up to the required depth at the base. Rocks are inherently anisotropic materials, showing variation in properties in different directions.

Yet, it is of great significance to know what class of rocks make up the area – igneous, sedimentary or metamorphic; and also which type and sub-type is more prevalent; and whether it is only one class of the rock existing there, or more types of the same or different classes of the rocks are found.

It is possible that the entire site may be made up of one type of rock, say, for example, fine textured sandstones; it is also possible that it may have alternate layers of sandstones, shales and clays, all of varying types. Complex lithology definitely poses challenging design problems.

(b) Structures:

Along with lithology, the structural features of rocks of the site are also thoroughly investigated. This involves detailed mapping of planes of weakness like bedding planes, schistosity, foliation, cleavage, joints, shear zones, faults and fault zones, folding and the associated features.

It is because each one of these features modifies the engineering properties of the rocks to a great extent. While mapping these features, special attention is given to recording their attitude, spacing and nature. Joints, for instance, may not be as harmful when sparsely developed and of a closed nature, but these may render the same rock very weak and permeable when profusely developed and of open type.

Shear zones have to be searched, mapped and treated with great caution. In some cases, these may be developed to such an extent that the rock may necessitate extensive and intensive rock treatment (e.g. excavation, backfilling and grouting etc.). In still other cases their development may be to an unmanageable scale. In such cases cost factors may demand the abandoning of the site for a better alternative.

Following is a brief account of the influence of more important structural features of rocks on dam foundations:

i. Dip and Strike:

The strength of sound, unfractured stratified rock is always greater when the stresses are acting normal to the bedding planes than if applied in other directions. This being so, horizontal beds should offer best support for the weight of the dam. The resultant force (due to weight of the dam and thrust of the impounded water) is always inclined downstream. As such, gently upstream dipping layers offer best resistance to the resultant forces in a dam. They also serve as a natural obstruction for leakage (Fig. 23.5C).

It is also easy to understand that the easiest direction for slippage in stratified rocks is along the bedding planes. Consequently, the most UNFAVOURABLE strike direction is the one in which the beds strike parallel to the axis of the dam and the dip is downstream (Fig. 23.5.B). It must be avoided as far as possible. Therefore, other conditions being same, beds with upstream dips are quite favourable sites for dam foundations.

ii. Faults:

These structures can be source of danger to the dam in a number of ways. Thus:

(i) The faulted rocks are generally shattered along the rupture surfaces;

(ii) Different types of rocks may be present on either side of a fault plane. Hence, sites with fault planes require great caution in calculating the design strength in various sections of the dam. In case some fault surface or zone gets ignored or overlooked, the stability of dam gets endangered.

(iii) Dams founded on beds traversed by fault zones and on major fault planes are more liable to shocks during an earthquake compared to dams on non-faulted rocks. This single factor in itself is of great importance, especially when the area in which dam is proposed happens to be seismically active. It is, therefore, always desirable to avoid risk by rejecting sites traversed by faults, fault zones and shear zones for dam foundations.

But when topographic, lithological and/or economic factors do not leave a choice for an alternative site, then the nature, extent and age of the fault should be thoroughly investigated. Generally small scale fault zones and shear zones can be treated effectively by grouting. But in the case of major shear zones, weak material would have to be excavated and the space backfilled with hard material like concrete up to the required depth.

iii. Folds:

The most notable effects of folds on rocks are – shattering and jointing along the axial planes and stressing of limbs. Consequently, dams aligned along axial regions of folds would be resting on most unsound rocks in terms of strength. Similarly, in synclinal bends dams placed on the upstream limbs would run the risk of leakage from beneath the dam. Further, the balance of forces in the stressed limbs would be disturbed if these are opened up during construction of diversion tunnels and galleries.

iv. Joints:

No sites are totally free from jointing. Hence, sites cannot be abandoned, even if profusely jointed. However, the detailed mapping of all the aspects and characters of jointing as developing in the rocks of proposed site has to be taken up with greatest caution. The geometry of joints, their intensity, nature and continuity with depth, all must be thoroughly established and their effects on the site rocks evaluated and remedial measures taken in advance.

Occurrence of micro-joints has to be established with still greater care as such joint systems, if left untreated, could be source of many risks. In the limestone rocks that formed foundation and abutments at Salal Dam in Jammu (Kashmir), the micro-joints presented considerable difficulties in detection and treatment.

Engineering Properties of Rocks :

Only lithological and structural studies are not fully sufficient for the selection of a site for a dam. A thorough testing – both in laboratory and in situ of the site rocks for their most important engineering properties has to be carried out. Such properties include – compressive strength, shear strength, modulus of elasticity, porosity, permeability and resistance to disintegration on repeated wetting and drying.

(a) Strength Parameters:

The determination of strength of the foundation rocks in the case of gravity dam and also of abutment rocks in the case of arch dams are considered starting points in working out designs of these dams. In either case construction of a dam involves transfer of a tremendous load due to the weight of the dam and weight and thrust of stored water on to a very small area of foundation or abutment rocks.

These loads are both of compressive and shearing nature. The capacity of the rocks vis-ά-vis these loads has to be clearly established. This is achieved by testing the strength properties in the laboratory on the core samples obtained from different and critical locations at the site using conventional laboratory techniques.

These are complimented with in-situ studies of the same properties using static and dynamic techniques. The static methods involve excavating trenches, tunnels or bore-holes within the rock mass at site and loading a section by pressure exerting machines such as hydraulic jacks. Settlements and strains are recorded at different load increments from which parameters like bearing strength, modulus of elasticity and Poisson’s ratio are calculated.

The dynamic methods involve creating seismic shocks artificially at selected locations and recording the velocity of shock waves so generated through the rocks of the site and the abutments. The shock wave velocity is related to the density, rigidity, porosity and permeability and structural constitution of the rocks.

Results obtained from all the three investigations, i.e. laboratory, in-situ static and dynamic testing are compiled and correlated to obtain a fair assessment of the strength parameters of the rocks at the site.

(b) Porosity and Permeability:

A dam is essentially a water impounding structure and as such water impounded by it must not find easy avenues of escape other than those provided in the design i.e. sluices and spillways. However, perfectly impervious rock throughout the site may not be available in all cases. Most rocks are permeable to some extent. It is, therefore, essential that investigations are carried out to establish fully the magnitude of permeability of the rocks at the site.

Porosity and permeability are also investigated, like strength related properties, both in the laboratory and in-situ. Programmes are then chalked out to make the rocks water tight, especially in critical zones, by artificial treatment, such as grouting.

Slaking Test:

This is an important test where rocks are weakly cemented or poorly compacted as in shales, argillaceous sandstones, conglomerates, limestones and pyroclastic rocks. Reservoir rocks, especially in the immediate upstream vicinity of the dam, are liable to be exposed a number of times in a year when water is drawn out from the reservoir for the proposed use.

They would undergo drying during the exposure. Similarly, when the water level rises during high precipitation time, these rocks are submerged. Such alternate drying and wetting may cause disintegration by crumbling and removal of cementing material and other mass wasting processes.

Essay # 5. Forces Acting on a Dam :

Any major dam is a highly complex engineering structure where more than one type of forces comes into play. A proper estimation and analysis of all these forces is essential to ensure stability of the dam.

In any dam, following type of forces are always involved:

(a) Weight of the Dam:

Each dam is a massive construction where thousands of tonnes of material are placed on limited space to form a huge barrier. In gravity dams and embankment dams, it is the weight of the dam which is primarily responsible for holding the water back on the upstream side. For calculating the total force due to the weight of the dam, it is divided into convenient units or sections and weight of each section acting on its centre of gravity is determined.

The resultant from all the sections is summed up and is taken as expression for the total weight acting at the C.G. OF THE DAM. Evidently, the forces arising due to the weight of the dam are compressive in nature. If by any chance, they happen to be greater than the allowable stresses of the material within or below the dam, the latter is likely to fail by crushing.

(b) Water Pressure:

Since the dam is supposed to impound water, it is required to resist horizontal forces acting due to weight of the water impounded on its upstream side. This water pressure can be calculated by using rules pertaining to hydrostatic pressure distribution (Fig. 23.8).

Thus, in a gravity dam with a vertical upstream face, the water pressure would be equal to W*H at the base of the dam and zero at the surface level, where W and H stand for the unit weight of water (1000 kg/m) and height of water in meters, respectively.

The resultant force due to the weight of the water on the dam would be given by the expression:

p = 1/2 WH 2

acting at H/3 from the base (i.e. at C.G. of the dam). When the upstream face is not vertical, (Fig. 23.8B) the weight due to water is resolved into horizontal component and a vertical component.

(c) Uplift Pressure:

Although it may be desirable to make a dam an absolutely impervious structure, it may be practically impossible at economic costs. Many pores and minute cracks and joints are left in the dam body and also in the foundation rocks. Water is likely to find its way into these minute openings through seepage and gradually fill them up.

It has been now fairly established that the trapped water exerts an upward pressure on the body of the dam which is, in no case, unimportant. This pressure, called the Uplift Pressure must also be assessed, analysed and accounted for in the dam design for ensuring stability of the structure.

In a gravity dam without a drainage gallery, the uplift pressure is broadly taken as of trapezoidal shape, being maximum at the upstream toe (equal to maximum reservoir head) and minimum at the downstream toe (equal to the tailwater head). In order to provide some built-in relief from the uplift pressure, drainage galleries are often provided in the dams. In other cases cut-off channels are constructed under the upstream face. A third method is intensive pressure grouting of the foundations to minimize chances of development of uplift pressure.

(d) Earthquake Forces:

Dams get disturbed during earthquakes like all the other structures standing on the ground. The disturbance in the dams would be highly dangerous because they store huge volumes of water under great hydrostatic head, which when let loose due to failure of dam, could create havoc.

Hence, dams that are constructed in areas known to be seismically active from the past records must necessarily be designed to withstand additional forces that are likely to arise during a future shock or shocks. The seismic forces, therefore, are the fourth major class that are supposed to be acting on the dams, besides those due to weight of the dam, weight of the water and uplift pressure.

An analysis of seismic forces liable to act on a dam during a shock is a highly complex problem, which needs solution from at least three aspects:

(a) Forces developing due to vertical acceleration of the ground during a shock both in an upward and in a downward direction.

(b) Forces developing due to horizontal acceleration when the reservoir behind the dam is empty (horizontal inertia force).

(c) Forces developing due to horizontal acceleration when the reservoir is full (the hydrodynamic forces).

It attempts analysis of such forces, except to mention some basic factors. Thus:

(i) While considering the effect of vertical acceleration, it is the acceleration in downward direction which is considered a greater threat to the stability of the dam;

(ii) While considering the effect of horizontal acceleration in reservoir full condition, the hydrodynamic force calculations must take into consideration the shape of the upstream face and also water pressure distribution in static conditions;

(iii) While considering the effects of horizontal inertia force, the direction in which the seismic shock is most likely to act should be chosen with great caution.

The dam safety designs would then demand incorporation of such additional strength in the dam so that it is capable of withstanding sum total of all the disturbing forces during a future shock without collapsing, overturning or bursting.

In most countries of the world including India, the land surface has been classified into zones of seismic activity. In areas of ‘high’ seismic activity, sub-zoning has also been attempted or could be attempted. A factor of safety is then taken into consideration while designing a dam in such an area. This is called ‘seismic factor’ and is expressed in terms of acceleration as a fraction due to gravity, e.g. 0.1 g, 0.15 g or 0.05 g and so on.

(e) Other Forces:

In addition to the above major forces acting on a gravity dam, forces caused due to silting in immediate vicinity of the upstream face (silt pressure) and due to the waves caused by strong winds blowing over the reservoir water may also be considered. Generally these types of forces are of theoretical significance only and easily ignored. Similarly in areas of cold climate, the top of surface in reservoirs may actually freeze and expand causing lateral forces between 25 to 150 t/m 2 . Their influence on the top line of dam structure may have to be considered carefully.

Essay # 6. Relative Suitability of Different Rocks :

The number of major dams constructed in different parts of the world runs in thousands; in India alone there are more than 4000 major dams constructed till the end of 20 th century. But, no two dams might be called duplicate of each other.

This is so because no two sites are exactly similar in all geological details and as such design of each dam has to be in accordance with the site conditions for that dam. Viewed from this angle a generalization regarding suitability of different rocks as dam sites may be erroneous. It may be, however, of great assistance and guidance value while choosing the sites for detailed investigations when choice is available.

It is from this angle that the following brief account of relative suitability has to be viewed:

(a) Igneous Rocks:

The massive igneous rocks like granites, syenites, diorites, gabbros, dolerites and the like may be classed among the excellent category as they possess compressive strength, shear strength and modulus of elasticity, far in excess than required for very high dams.

When undisturbed by secondary processes such as folding and faulting and unaffected by weathering and erosion, these are invariably almost impermeable. But, difficulties may arise even with these rocks when they are frequently traversed by planes of weakness such as fault zones, shear zones, joints, disconformities and secondary intrusions, or, when they are highly weathered in localized zones.

Similarly, rocks of igneous origin but volcanic character have to be viewed with great caution.

Three main types of difficulties may arise with such rocks:

(i) When congealed in layered form, their contact planes may also be planes of weakness;

(ii) In between the volcanic rock layers, thick or thin sedimentary layers be intervening (the intertrappean beds) causing heterogeneity and variation in reaction to the applied loads;

(iii) Sometimes these may be rich in interconnected cavities left due to escape of gases from lava during cooling, rendering them quite permeable.

However, other things being the same, sites made up of igneous rocks are generally safe and stable and more suitable.

(b) Sedimentary Rocks:

Massive, well-cemented, thoroughly compacted and fine textured sedimentary rocks generally form sound, stable and durable sites for dams. But when rocks of this group occur in a deformed and profusely jointed or layered fashion, great care and caution are necessary while placing dams on them.

Sandstones with siliceous cements (quartzites) are generally reliable. Those varieties of sandstones which have clayey or ferruginous cements, and those rich in mica and other weak minerals may require thorough treatment for improving their qualities. Joints occur in almost all sedimentary rocks and must be thoroughly studied and treated. Sandstones form the major rocks at the site of Bhakra Dam in India.

Limestones, which are carbonate type sedimentary rocks, are always to be viewed with caution. These are more often richly traversed by solution cavities and channels. They are also open to gradual solvent action of water, which of course cannot be overlooked.

In spite of these negative points, massive, thoroughly compact and fine-textured limestones form quite sound foundations when these defects are properly taken care of. The well-known Salal Dam in Jammu is located in a limestone region and site rocks are fine textured dolomitic limestones often traversed by micro-joints.

Shales are perhaps the most troublesome sedimentary rocks as far as their suitability for dam sites is concerned. Thoroughly compacted and well cemented and hardened shales may prove to be quite suitable. However, the common varieties – soft, friable and too clayey shales – can hardly be trusted as foundation rocks.

In fact, even the apparently suitable shales often present a variety of problems chief among which are:

(i) Gradual consolidation under load that may lead to too much settlement of the dam (and hence create risk of failure);

(ii) Liability to shear failure when these happen to occur in thin layers inclined downstream;

(iii) Rapid deterioration under conditions of alternate wetting and drying when these happen to form abutment rocks;

(iv) Unpredictable elastic constants.

In view of the above negative qualities shales and clays are always considered among unreliable sites for dams.

(c) Metamorphic Rocks:

This group of rocks exhibits greatest variation in terms of suitability for dam sites. Some varieties are hard, compact, thoroughly crystalline, well-knit and massive and the ideal rocks for dam foundations such as granitic gneisses, quartzites and marbles. However, some other varieties like schists, slates and phyllites may pose considerable troubles, and require very thorough investigations with regard to their filiation, mica content, fracturization, cleavage and so on.

Still, many dams have been located even on these rocks after proper investigations and treatment. The Dul Hasti Project in Kistwar (J & K – India) and the Uri Project, also in Kashmir, India, have gneissic and phyllitic rocks as their sites. Schists and mylonites occur in parts at the Hirakud dam site in Orissa.

Essay # 7. Geological Problems after Dam Construction :

Erosion below Spillways :

The Problem:

Reservoir water discharged over the spillway of dam generally acquires such velocities that are capable of causing deep erosion in any type of soil or rock below the spillway. Silt, sand, gravels and boulders are easily removed by such action whereas rocks with open joints or bedding planes are virtually plucked out of their places gradually but surely.

The aim of all methods of control of erosion below the spillways should be to dissipate the extra energy that reservoir water gains due to increased velocity during fall below spillway. The best method for dissipating extra energy within a limited space is to make the falling water strike against the tail water in a properly designed manner.

This would result in dissipation of extra energy in creation of turbulence in the tailwater and not in too much affecting the base materials of the river bed below. A simple method for producing such turbulence is by creating a hydraulic jump below the spillway. For this jump to occur, the most essential condition is a requisite depth below the jump.

So, the main problem with the dam design engineer is to obtain the required depth:

(i) Either, by constructing a small auxiliary dam below the apron or by excavating the river bed when the depth of the tail water is insufficient to create the jump;

(ii) Or, in case the water depth is more than sufficient for the birth of the jump, by providing a sloping apron;

(iii) Or, by devising any other economic methods.

Related Articles:

• Forces Acting on a Gravity Dams (With Diagram) | Geography
• Essay on Geology
• How to Improve the Strength of Rocks: 3 Methods | Geology
• Essay on the Mineral Resources of India | Geology

Essay , Geology , Dams , Essay on Dams

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New York City, federal and regional partners renew study of broader uses for Lehigh River dam

• Updated: Sep. 18, 2024, 3:56 p.m.
• | Published: Sep. 18, 2024, 3:45 p.m.

Francis E. Walter Dam was finished in 1961 dam on the Lehigh River, in Carbon and Luzerne counties, about 77 miles upstream of the confluence with the Delaware River in Easton. U.S. Army Corps of Engineers

• Kurt Bresswein | For lehighvalleylive.com

A study now estimated at nearly $8 million aims to determine how Francis E. Walter Dam on the Lehigh River can aid its surrounding Delaware River Basin.

New York City along with federal and regional partners on Tuesday signed a cost-sharing agreement amendment for the re-evaluation of existing and future uses of the dam.

The amendment carries a shared study cost projected to be $7.95 million, with a total study period of 89 months from the agreement’s original effective date of Sept. 25, 2019. That puts the completion date around the end of February 2027. The study was originally expected to cost $2.6 million.

A January 2020 meeting held near the Pocono Mountains dam to introduce the study drew a standing-room-only crowd of some 500 people . Anglers and whitewater rafting companies at that time just prior to the coronavirus pandemic sought assurances the study would not jeopardize the dam’s role in supporting recreation on the Lehigh River — that’s one of its missions now, secondary to flood protection.

Tuesday’s Francis E. Walter Dam Re-Evaluation Study Federal Cost Share Agreement (FCSA) Amendment was signed by leaders from the U.S. Army Corps of Engineers, Delaware River Basin Commission and New York City Department of Environmental Protection.

Clockwise from left, Delaware River Basin Commission Executive Director Steve Tambini, Assistant Secretary of the Army for Civil Works Michael Connor, U.S. Army Corps of Engineers Maj. Gen. Jason Kelly, Paul Rush from the New York City Department of Environmental Protection, New York City Department of Environmental Protection Commissioner Rohit Aggarwala and Army Corps Philadelphia District Commander Lt. Col. Jeffrey Beeman take part in a ceremony to sign a feasibility cost sharing agreement amendment for the Francis E. Walter Dam Re-evaluation study Tuesday, Sept. 17, 2024, at Delaware River Basin Commission headquarters in West Trenton, New Jersey. Courtesy photo | For lehighvalleylive.com

The amendment does not mean the study is starting over at square one, Army Corps spokesman Steve Rochette told lehighvalleylive.com . Rather, it aims to provide adequate time and resources to complete a full re-evaluation of the dam’s role in the basin. This includes additional environmental modeling and engineering analysis, the corps says.

“There is more of a refined focus at this time,” Rochette said.

According to an Army Corps news release , the study will evaluate the existing and future use of the Francis E. Walter Dam Reservoir during Delaware River basin emergency drought conditions to support/aid salinity repulsion in the Delaware Estuary, provide low flow augmentation and protect aquatic life.

Pushing back the Delaware River/Estuary salt front now relies entirely on water releases from New York City’s three Delaware River drinking water reservoirs. The Army Corps and its study partners previously said there is no question that all of the Francis E. Walter Dam Reservoir water will continue to flow down the Lehigh River , which joins the Delaware River at Easton.

“Co-sponsoring this study will support drought management planning, increase climate resilience in our shared Delaware River Basin, and ensure that all Basin states are represented in the process,” the basin commission’s executive director, Steve Tambini, states in the release.

New York City DEP Commissioner Rohit T. Aggarwala stated: “Having the foresight and courage to update long-held water management practices throughout the Delaware River basin is critical in confronting the new realities of climate change.

“This agreement enables out-of-the box thinking, backed by world-class science and engineering analysis, to help ensure a more vibrant and healthier river basin for future generations while maintaining the critical protections to surrounding communities that all of us are committed to,” Aggarwala continued.

more lehigh valley outdoors news

• Late hummingbirds still buzzing about, and ever tried a Jerusalem artichoke? | Lehigh Valley Nature Watch
• Easton trail’s newest work being installed ahead of weekend reception celebrating the artist
• New ‘highly destructive’ invasive species of insect found in Pa. for the first time
• Finding habitat, porcupines expanding their territory into Lehigh Valley region
• New mushroom species just dropped, and it’s a Lehigh Valley discovery

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Home — Essay Samples — Environment — Alternative Energy — The Dangers and Risks of Dams

The Dangers and Risks of Dams

• Categories: Alternative Energy

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Words: 935 |

Published: Aug 24, 2023

Words: 935 | Pages: 2 | 5 min read

Table of contents

Introduction, types of dams and their functions, natural and environmental consequences, flooding and dam failure, displacement and social impact, geological and seismic risks, climate change and dam vulnerability, mitigation measures and regulation, case studies.

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