In other areas where the groundwater is close to the surface, water may pond on the surface when there is a period of sustained rainfall. Groundwater also discharges periodically to spring or seepage areas when groundwater recharge exceeds subsurface capacity. In the case of coastal wetlands, because tides vary with the seasons, this storage role has a major impact on the types and abundance of vegetation and wildlife. Similarly, in the case of freshwater wetlands, this storage capacity plays a vital role releasing water to lakes and streams to help maintain water levels needed for fish and wildlife, especially during critical spawning seasons, and for recreation uses. The value of water storage is most easily seen in terms of flooding events.
Wetlands play a vital role in controlling floods.
Wetlands help to lessen the impacts of flooding by absorbing water and reducing the speed at which flood waters flow. Upstream wetlands can serve to store flood waters temporarily and release them slowly downstream. Along rivers, wetlands usually form natural pathways for flood waters from upstream to downstream points. If those pathways are altered or removed, flood waters can go elsewhere, potentially damaging property and threatening public safety. Without wetlands as a natural flood control mechanism, flooding can become more severe.