Some dams are constructed with a gate that is designed to release sediment from a river downstream into the river. Sometimes a reservoir can be dredged a process where sediment is removed from the reservoir to increase its storage capacity. This is typically done in reservoirs that collect a lot of smaller particles like silt and mud, unlike the rivers in Alberta that have more gravel and sand.
Glenmore Reservoir is located on-stream on the Elbow River in western Calgary. The reservoir was constructed in In the reservoir was surveyed to assess the amount of sediment that had accumulated over the years.
In the 36 years that the reservoir had been operating, it had lost ten percent of its storage capacity due to sedimentation. Currently, the bottom of the reservoir is covered in silt, sand and clay. The amount of silt entering the reservoir is relatively consistent annually. During years with floods, the amount of sediment flowing through the reservoir is much higher, however a large portion of this sediment flows over the spillway, downstream of the reservoir [2].
There has been an ongoing debate regarding dredging Glenmore reservoir. There is potential to increase the total water storage capacity and increase the amount of live storage which is used for flood control.
However, the benefits might not justify the costs. The report also stated that the cost of dredging would end up being millions of dollars [3]. Bathymetry is the mapping of an underwater surface, such as the seafloor or the bottom of a lake or reservoir. In order to map a reservoir, the topography of the area is recorded before a reservoir is filled. Once the reservoir is filled, bathymetric surveys are used to monitor the bottom. These surveys are useful, because overtime sediment will build up in the reservoir and the surveys can help determine the amount of sediment.
Dredging is the act of scraping out accumulated debris and sometimes sediment that has accumulated at the bottom of a reservoir. Dredging is often very expensive so before it is undertaken a full cost-benefit analysis is completed to ensure that the benefits of dredging outweigh the costs.
As an example, the City of Calgary commissioned an independent report on the merits of dredging the Glenmore Reservoir. The report concluded that the increased capacity that could be gained by dredging would be small and would provide a maximum two percent reduction in moderate flood events one in fifty year events, or and less for larger events.
After the floods in southern Alberta, some reservoir maintenance options for flood mitigation were considered. The report also considered assessing the value of dredging TransAlta reservoirs such as Ghost Lake. It is important to consider whether lost storage capacity in TransAlta reservoirs could be regained by dredging the reservoirs to remove the sediment and aggregate that has accumulated over many years.
Dredging was suggested by some stakeholders as a more cost-effective means of gaining storage in the headwaters when compared to raising existing structures or building new structures [5]. Ghost Reservoir was presented as a specific example where dredging should be investigated. TransAlta indicated its position that dredging Ghost Reservoir would regain little capacity in terms of live storage. In addition, the City of Calgary determined that dredging Glenmore Reservoir for flood mitigation would have negligible benefits [6].
If a reservoir is built in an area where silt is expected to accumulate quickly, gates will be installed at the bottom of the dam. Periodically, operators can open the gates to release the sediment load downstream so that it goes back into the river system.
Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. For thousands of years, humans have modified the physical environment by clearing land for agriculture or damming streams to store and divert water.
As we industrialized, we built factories and power plants. For example, when a dam is built, less water flows downstream. This impacts the communities and wildlife located downstream who might depend on that water.
Use these resources to teach your students how humans modify the physical environment and the compounding impacts those changes have. Individuals, communities, and countries depend on a variety of different resources to help them thrive: electricity, timber, oil, water, and food to name a few. Because these basic resources are such a large part of our daily lives, it is important that we manage them responsibly to ensure future generations have what they need.
Human civilization heavily impacts the environment and the rich natural resources we depend on. All communities face the challenge of managing resources responsibly, not only for themselves, but for the sake of the world around them. Learn more about how individuals and communities can manage their resources to support themselves and the world around them. Freshwater is a precious resource on the Earth's surface.
It is also home to many diverse fish, plant, and crustacean species. The habitats that freshwater ecosystems provide consist of lakes, rivers, ponds, wetlands, streams, and springs.
Use these classroom resources to help students explore and learn about these places. Students investigate the interconnectedness of Earth's water reservoirs by learning about the hydrosphere. They then discuss ways in which humans are connected to and alter those reservoirs, especially the ocean. A dam is a structure built across a stream or river to hold water back. Dams can be used to store water, control flooding, and generate electricity. Hydroelectric energy is power made by moving water.
The stored water can be used for irrigation, drinking water after purification or to produce energy. Precipitation , Freshwater , Treated Water. A reservoir is an artificial lake called man-made reservoir. It can be formed by building a dam across a valley, by excavating the land or by surrounding a piece of land with dykes and diverting a part of the river flow into the reservoir.
The water is stored in the reservoir and can be used for irrigation , hydro-power or as a water source for domestic or industry use. Man-made reservoirs are also very effective constructions to control unexpected floods see also stormwater management. A reservoir is fed by precipitation, rainwater runoff or from a constant flow of a river. Water loss can occur due to evaporation especially in arid regions and depending on the reservoir bottom due to percolation small reservoirs are often lined.
Sediments from rivers or surface runoff can reduce the storage volume of a man-made reservoir significantly FAO Water stored in a valley usually has a higher level than the valley bottom downstream of the dam.
Because of this difference in level, the valley can be irrigated by a gravity system or other distribution systems. Water can be taken from the reservoir via a concrete or steel pipe. This pipe connects the reservoir to an irrigation canal downstream. A valve is usually located on the upstream end of the pipe to control the discharge of water into the canal FAO The kinetic energy of reservoirs is often used to produce electricity see also hydropower small-scale and hydropower large-scale.
Where no such water-body previously existed the presence of a reservoir in a drainage basin and the abstraction of significant water amounts for storage upstream significantly impacts the watercourse, the flora and fauna, and the human inhabitants in the drainage basin. These potential impacts should be identified and thoroughly examined prior to reservoir construction, in order to comprehensively assess the total value of the reservoir project.
Such an assessment is now obligatory by law in many countries for all new dam constructions UNEP Ecological impacts of reservoir dams have been reported from various aspects such as barrier for migratory animals like anadromous fish, eutrophication of reservoirs by plankton blooming, decreasing flow volumes in tail waters, stabilisation of flow regimes by flood peak cut, changes in thermal regimes of river water, river bed degradation and increase in substrate grain size by sediment trapping, etc.
Furthermore big dams and extraction of water e. Like lakes , reservoirs range in size from pond-like to very large water-bodies e. Lake Powell, U. The variations in type and shape, however, are much greater than for lakes.
The latter reservoirs are sometimes called embankment or bounded reservoirs, and have controlled inflows and outflows to and from one or more rivers. The fields located around the reservoir upstream of a dam or surrounding a natural lake are higher than the reservoir or lake's water table. Dirt and other small particles are usually removed by filtering the water through beds of sand and gravel, or by adding chemicals that cause the particles to stick together so that they can be separated off from the water.
Once the water is treated, it is transferred to a service or storage reservoir ready for distribution. Service reservoirs are covered reservoirs. In the UK, there is a network of tens of thousands of kilometres of underground pipes that carry billions of litres of clean water every day to homes, offices, schools, factories and hospitals.
Reservoirs can be used to store water to feed hydroelectric power stations. Hydroelectric power is generated by using the energy from falling water to drive water turbines that in turn drive electric generators.
The reservoir water is stored at a higher level than the turbines, which are housed in a power station. Sometimes, the power station is directly in front of a dam, and pipes through the dam feed water directly to the turbines.
In other cases, the power station is some distance downhill from the reservoir, and the water is fed to it through long pipes or tunnels called penstocks. Water from snow and rainfall will find its way into stream and rivers and eventually into the sea. After severe storms, or heavy snow or rain over a number of days, the water level in rivers can rise dramatically.
Sometimes, the water flows over riverbanks or walls causing flooding of farmland, property, and in the worst cases, loss of life.
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