Dams are vital infrastructure that significantly contributes to flood control and prevention by regulating river flows.
How Dams Aid in Flood Control
The primary mechanism by which dams assist in flood control is through the creation of large reservoirs upstream. These reservoirs act as holding basins for excess water during periods of heavy rainfall or snowmelt.
- Storing Floodwaters: When river levels rise rapidly, the dam holds back the surge, storing the varying volumes of floodwaters in the reservoir. This prevents the peak flood flow from immediately rushing downstream, which is often the cause of widespread flooding.
- Regulating Water Discharge: Beyond simply holding water, dams allow for the meticulously controlling the timing of water discharge. Instead of releasing all the water at once, reservoir operators can release water gradually over a longer period, after the flood threat downstream has diminished.
Operational Management for Prevention
Effective flood control by dams relies heavily on skilled management. Reservoir operators follow specific operational rules designed to maximise the dam's capacity to absorb flood events.
- Balancing Levels: Operators must strike a balance between drawdown levels before the flood season and the prevention or minimisation of spillage. This means intentionally lowering the water level in the reservoir ahead of expected heavy rain periods. This "drawdown" creates available storage space to capture incoming floodwaters.
- Minimising Spillage: By managing the storage and controlled release, the goal is to avoid or minimise spillage (water flowing uncontrolled over the dam's spillway), which can exacerbate downstream flooding.
In essence, dams transform unpredictable, large-scale flood events into manageable, controlled releases, thereby reducing the risk and severity of flooding in downstream areas.
