Influence of Wetlands on Black-Creek Hydraulics

Abstract

The influence of wetlands on basin hydrology and channel hydraulics has been investigated for a small Canadian basin using the MIKE 11/NAM model of the Danish Hydraulic Institute (DHI). The Black Creek basin has an area of 93.58 km2, 15.6% of which consists of wetlands. The methodology involved long-term continuous simulation of the basin with and without the wetlands. The present analysis shows that on an annual basis, wetlands reduce the total runoff by less than 1% and increase the evapotranspiration by about the same amount. Overland flow decreases 21% and base flow increases by 15% due to wetland presence. Groundwater recharge also increases by 15%. During individual runoff events, wetlands reduce runoff by about 5% and 1% in terms of peak and volume, respectively. The 1:100-year flood under current conditions would become a 1:35-year flood if wetlands were removed. Wetlands can suppress the snow-melt-generated flood peaks by about 15–20% during spring freshet and summer floods by 1–5%. Wetlands also reduce the water level by 3–5 cm and 5–8 cm during spring freshet and summer storms respectively. Channel flow, water level, and velocity are influenced by the wetlands only during rare flood events.