A stochastic approach to designing wetlands for stormwater pollution control

Central to wetland design for stormwater pollution management is the proper control of the hydrologic regime of these wetlands and wet detention basins. The paper proposes a stochastic approach in determining the appropriate wetland size for stormwater treatment in recognition of the inherent variability of stormwater runoff and pollutant load generation within a storm event and between storm event. The determination of wetland size would include the use of stochastic generation of stormwater runoff and continuous wetland behaviour simulation. A typical design chart summarising the interaction between wetland size, prescribed retention period of stormwater and wetland hydrologic effectiveness for Melbourne is presented. The chart enables the selection of the appropriate storage volume and outlet characteristics on the basis of long-term average effectiveness of the wetland to retain stormwater over a desired minimum period rather than a prescribed level of performance for an individual probablistic event.