FEM-Modelling of Open Stormwater Detention Ponds

Stormwater in urban areas is polluted with suspended materials which transport heavy metals and degrade the quality of the receiving waters. Since open detention ponds improve water quality, an investigation of a constructed pilot-scale detention pond was carried out. Measurements of inflow and outflow were performed and two flow-weighted samplers were used to collect representative samples of suspended solids and heavy metals. The particle size distribution was analysed to allow an estimation of the settling of suspended solids. Particle removal from a rain event was defined as two different phases where the first phase occurs during the rain event and the second phase after the event. In this paper only the first phase is considered. A FEM-software package (FIDAP) was used to calculate the three dimensional velocity flow field for one rain event. A sedimentation approach was applied to the flow field where paths were calculated through the detention pond for different particle sizes. The results from four different particle sizes show satisfactory agreement between FEM-calculated and observed particle removal. The results show that FIDAP is a useful tool to predict pollutant removal for open detention ponds with arbitrary geometry