Designing outlet characteristics for optimal wetland performance

Central to the hydrological and botanical design of constructed wetlands for stormwater quality management is the proper control of their hydrologic regime. The hydrologic regime, defined as the probabilistic distribution of inundation depth in the wetland, reflects the inherent variability of storm inflows to the wetland and is directly influenced by the discharge characteristics of the outlet structure of the wetland. The influence of three typical outlet structures on the hydrologic regime of a hypothetical wetland was investigated using a continuous simulation approach. The three outlet types investigated were that of a culvert, a riser and a siphon. Simulations found that all three devices provides equally effective control of the ability of the wetland to capture and detain storm runoff but can have different influence on the hydrologic regime of the wetland. The siphon-controlled wetland was found to exhibit a more even distribution of inundation depth compared to the other two outlet types.