A reservoir is a large body of water that is stored for later use, serving as a holding basin for water resources. While the concept of water storage is ancient, the modern understanding of a reservoir often implies human influence and intentional design. The term inherently involves the containment of water. This storage allows societies to maintain a steady water supply even when natural water flow fluctuates throughout the year.
The Distinction Between Natural and Artificial Reservoirs
The term reservoir technically applies to both natural and artificial bodies of water. Natural reservoirs include large lakes formed by geological processes or underground formations like aquifers that naturally store water. However, in common usage, particularly in infrastructure and civic planning, a reservoir refers almost exclusively to an artificial creation.
Artificial reservoirs, sometimes called man-made lakes, are constructed specifically to manage water resources for human purposes. These impoundments are the result of deliberate civil engineering efforts, unlike lakes that form naturally over geological timescales. They are typically created to serve specific municipal or water resource management needs, such as providing a reliable source of drinking water.
The Engineering of Artificial Reservoirs
The creation of an artificial reservoir is achieved through impoundment, which involves constructing a dam across a flowing river or stream. This barrier holds back the water, allowing it to pool and flood the valley behind it. The dam location is often selected at a narrow point in a valley downstream of a natural basin, which maximizes the storage volume while minimizing construction material.
The dam is one component of the engineered system, which also includes structures designed for water control and safety. A spillway is a controlled release channel for excess water during high-flow events like heavy rain or snowmelt. This mechanism safely discharges floodwaters to prevent the water level from overtopping and damaging the main dam structure.
Water is released from the reservoir through outlet works, which are conduits or pipes that pass through or around the dam. These outlets are controlled by valves or gates to regulate the flow downstream for various uses. Intake structures draw water from the reservoir and are sometimes designed as towers with multiple ports at different depths to access the best water quality, avoiding surface debris or bottom sediment.
Essential Roles and Uses
Artificial reservoirs are constructed to fulfill several societal needs, with the most common function being the provision of water supply for human consumption and agriculture. They store precipitation and runoff during wet periods to ensure a continuous supply during drier seasons. The stored water is released to feed water treatment plants or diverted into irrigation networks for crop production.
Hydroelectric Power Generation
A significant function of large reservoirs is hydroelectric power generation, which converts the potential energy of the stored water into electricity. Water is released through penstocks, large pipes that guide the flow to spin turbines connected to electrical generators. This process utilizes the difference in elevation between the reservoir surface and the turbine location to create mechanical energy.
Flood Control
Reservoirs also play a substantial role in flood control by managing seasonal runoff and mitigating the impact of severe storms on downstream communities. By maintaining a lower water level during periods of expected heavy rainfall, the reservoir can absorb and hold back large volumes of water. The controlled release of this water over a longer period prevents sudden flooding in the river systems below the dam.