Ponds and Lakes

The ability of water bodies to store water helps them to attenuate flood peaks. A pond or lake intercepts overland flow and retains it until its storage capacity is full, before it starts overflowing and contributing to the downstream river flow. When a flood wave enters a lake, it is not transmitted directly to its outlet, but gets partly absorbed within the water body as the water level rises. Thus, when the maximum outflow is reached, there is also a large volume of stored water, which flows out with a time lag depending on the outlet characteristics, thereby attenuating flood peaks and slowing down their transmission downstream. The extent to which ponds and lakes play a role in flood alleviation during an extreme flood event depends on their type, location, the surface area, shape of the water body, the antecedent conditions and the hydraulic behaviour of the outlet.

Moreover, lakes and ponds provide a variety of ecological services, including drinking water supply, fishing, irrigation, recreation and livelihoods (e.g. agriculture, fishing, livestock production, etc.). Water bodies also assimilate plant nutrients, retain sediments and recharge groundwater. They are rich in plant varieties and are the main life support mechanism for many plant and animal species, as well as migratory birds.


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