Wetlands and Flood Management

Wetlands are ecosystems, which can be found where the soil is permanently or intermittently saturated (or inundated) with water and has vegetation that tolerates high moisture levels. There are many different types of wetlands including:

 

Marshes: Common in floodplain areas near the lower reaches of a river; characterized by low grassy vegetation and peaty soil that can hold very large amounts of water.

Estuarine or tidal wetlands: Reed beds, salt marshes, mangroves or mudflats at a river mouth or landside of a lagoon; can provide protection from tidal floods.

Riverine wetlands and forested wetlands: Wooded or shrub areas immediate to a river; can absorb small increases in flow and prevent localized floods.

Shallow lakes and ponds: Occur in depression areas of a landscape; can act as a reservoir during a storm and release water slowly to the aquifer or natural waterways; important in urban or agricultural areas to regulate overland floods.

Wetlands can provide important ecosystem services for flood and disaster risk management:

Retain and detain flood flows and stormwater.

Wetlands can help manage the flow of water for example by gradually releasing water into downstream ecosystems (sea, rivers and groundwater aquifers) which will reduce the amount of water that flows over the surface of the land.

Improve water quality through filtration.

Wetlands primarily help filter water in two ways: firstly, by slowing the flow of water, sediment in the water can settle to the bottom of the wetland; and secondly, vegetation in the wetland can absorb excess nutrients reducing the amount of contaminants from urban/agricultural areas that reach downstream aquatic ecosystems.

Reduce the impact of storm surge and coastline erosion.

Wetlands can reduce the speed of waves and wetland plants helps prevent coastal erosion by anchoring sand and soil.

Healthy wetlands can help manage flash floods, storm surge, and localized flooding (particularly in urban areas). In general, a watershed with more wetlands is better able to absorb floodwater, although extreme weather events have the potential to overload any system. From a risk management perspective, wetlands can be managed and restored as natural ways to reduce risk from flood waters; in many cases, climate-informed wetland restoration is a low-cost method for managing potential flood risk.