Connecticut Water Trails Association
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Connecticut Water Trails Association |
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Connecticut Water Trails Program Types Of Water Ways Reservoirs
What Is A Reservoir?
A reservoir is a storehouse or an artificial lake used to store water until it is needed. They come in all shapes and sizes. Reservoirs are owned by a water company or authority.
Types of Reservoirs
Valley Dammed Reservoir
A dam is constructed in a valley and uses the natural topography to provides the basin to form the reservoir. The dams are typically located at a narrow part of a valley downstream of a natural basin. The sides of the valley act as natural walls with the dam constructed at the narrowest point of the valley to give the dam the needed strength and keep the construction costs down.
In most reservoir construction projects people
have to be moved and re-housed, historical artifacts moved or rare
environments relocated a good example of this is
Candlewood Lake in Fairfield
County. When building reservoir in a valley the river is most often diverted through a temporary tunnel or by-pass channel.
Existing lakes are often enlarged in hilly regions to form reservoirs. Sometimes in these reservoirs the new top water level exceeds the watershed height on one or more of the feeder streams. Additional side dams are required to contain the reservoir in these cases.
If the topography is not suited to hold a single large reservoir, a number of smaller reservoirs may be constructed in a chain. Bank-Side Reservoir
These types of reservoirs involve taking water from a river and constructing a bank-side containment area able to store the water pumped from the river. Such reservoirs are usually built partly by excavation and partly by the construction of a complete encircling bund or embankment. Both the floor of the reservoir and the bund must have an impermeable lining or core, often made of puddled clay. The water stored in such reservoirs can be stored for several months during which time normal biological processes are able to substantially reduce many contaminants and almost eliminate any turbidity.
The use of bank-side reservoirs also allows a water removal to be closed down for extended period at times when the river is unacceptably polluted or when flow conditions are very low due to drought.
Service Reservoir
Service reservoirs store fully treated potable water close to the point of distribution. Many service reservoirs are constructed as water towers, often as elevated structures on concrete pillars where the landscape is relatively flat. Other service reservoirs are entirely underground, especially in more hilly or mountainous country.
Service reservoirs perform several functions including ensuring sufficient head of water in the water distribution system and providing hydraulic capacitance in the system to even out peak demand from consumers enabling the treatment plant to run at optimum efficiency. Large service reservoirs can also be managed to so that energy costs in pumping are reduced by concentrating refilling activity at times of day when power costs are low.
How Are Reservoirs Made?
Reservoirs are either man-made or natural. Natural ones are part of the land and are not made by people. Lakes and ponds are natural reservoirs.
Building a man-made reservoir is a big job. It takes from 5-8 years to plan, three years to build, and costs lots of money, too.
Water companies were
asking questions like: How do we get water to meet the needs of the
people? How are we going to meet these needs in the future as more and more development takes place?
The goal is to make sure that when people turn on water it is always there. This is known as a 'never-ending' supply.
Planning is important in making a reservoir. Once the engineers find a good water source, they decide how large the reservoir needs to be. They begin to buy any property that will be under water when the reservoir is done.
A large structure is built to send the water out of the reservoirs. It goes to the towns and water companies that buy it. The amount of water going out of the reservoir is controlled here. Inside this building is a crane-like machine that lifts panels and drops them into a slot to cover the openings. This lets less water out of the reservoir.
When there is a whole lot of rain or melting snow, a reservoir can get too high. Spillways are made so that water can overflow into nearby rivers and streams to keep the reservoir at the level they want it.
Wetlands and watersheds are important to your
water supply AND our environment.
How Does A Reservoir Work?
Water flows into reservoirs from different sources. It can be surface water from lakes, rivers, streams, and rain. It can also be from groundwater sources. Any of these can flow into the reservoir naturally--that is, without help from man. The reservoir could be in a place where the water would flow into it by itself. Other reservoirs have water pumped into them and might be further away from where the water actually comes from. Some reservoirs have pumped and natural water.
When water leaves the reservoir, it is not treated for anything. That is the job of the town that buys the water. It does get a little filtration before it leaves. This is done to take out big things that fall in the water so that they don't jam up the pipes and machinery when it is pumped to other places.
Uses
Direct Water Supply
Many dammed river
reservoirs and most bank-side reservoirs are used to provide the raw
water feed to a water treatment plant which delivers drinking water
through water mains. The reservoir does not simply hold water until it
is needed; it can also be the first part of the water treatment process.
The time the water is held for before it is released is known as the
retention time. This is a design feature that allows particles and silts
to settle out, as well as time for natural biological treatment using
algae, bacteria and zooplankton that naturally live within the water.
However natural limnological processes in temperate climate lakes
produces temperature stratification in the water body which tends to
partition some elements such as manganese and phosphorus into deep, cold
anoxic water during the summer months. In the autumn and winter the lake
becomes fully mixed again. During drought conditions, it is sometimes
necessary to draw down the cold bottom water and the elevated levels
of manganese in particular can cause problems in water treatment plants. Hydroelectricity
Reservoir generating hydroelectricity includes turbines connected to the retained water body by large-diameter pipes. These generating sets may be at the base of the dam or some distance away. Some reservoirs generating hydroelectricity use pumped re-charge in which a high-level reservoir is filled with water using high-performance electric pumps at times when electricity demand is low and then uses this stored water to generate electricity by releasing the stored water into a low-level reservoir when electricity demand is high. Such systems are called pump-storage schemes.
Connecticut Hydroelectric Power Controlling Watercourses
Reservoirs can be used in a number of ways to control how water flows through downstream waterways.
Downstream Water Supply – water may be released from an upland reservoir so that it can be used for drinking water lower down the system, sometimes hundred of miles further down downstream
Irrigation – water in an irrigation reservoir may be released into networks of canals for use in farmlands or secondary water systems. Irrigation may also be supported by reservoirs which maintain river flows allowing water to be abstracted for irrigation lower down the river.
Flood Control – also known as a “balancing" reservoir, flood control reservoirs collect water at times of very high rainfall, then release it slowly over the course of the following weeks or months. Some of these reservoirs are constructed across the river line with the forward flow controlled by an orifice plate. When river flow exceeds the capacity of the orifice plate water builds behind the dam but as soon as the flow rate reduces the water behind the dam slowly releases until the reservoir is empty again. In some cases such reservoirs only function a few times in a decade and the land behind the reservoir may be developed as community or recreational land. A new generation of balancing dams are being developed to combat the climatic consequences of climate change. They are called "Flood Detention Reservoirs". Because these reservoirs will remain dry for long periods, there may be a risk of the clay core drying out reducing its structural stability.
Canals – Where a natural watercourse's water is not available to be diverted into a canal, a reservoir may be built to guarantee the water level in the canal; for example, where a canal climbs to cross a range of hills through locks.
Recreation – water may be released from a reservoir to artificially create or supplement white-water conditions for kayaking and other white-water sports. In rivers containing salmon special releases are made to encourage natural migration behaviors in fish and to provide a variety of fishing conditions for anglers.
Flow Balancing
Reservoirs can be used to balance the flow in
highly managed systems, taking in water during high flows and releasing
it again during low flows. In order for this to work without pumping
requires careful control of water levels using adjustable sluices.
Accurate weather forecasts are essential so that dam operators can plan
drawdowns prior to a high rainfall or snowmelt event. Recreation
The water bodies provided by many reservoirs
often allow some recreational uses such as fishing, boating, and other
activities. Special rules may apply for the safety of the public and to
protect the quality of the water and the ecology of the surrounding
area. Many reservoirs now support and encourage less informal and less
structured recreation such as natural history, bird watching, landscape
painting, walking and hiking and often provide information boards and
interpretation material to encourage responsible use. What Are Problems For A Reservoir System?
Some of the water from
reservoirs may go into nearby rivers. River levels need to be
watched to make sure that they are not storing so much water that the
river levels go down. Imagine what it would be like if you were
out on the river in a boat--and water levels dropped very low!
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