Ecology Ditch: A Best Management Practice for Storm Water Runoff Mitigation

Abstract

A full-scale physical model of a modified infiltration trench was constructed to test a new storm water best management practice called an ecology ditch. The ditch was constructed using compost, sand, and gravel, and a perforated drain pipe. A series of 14 tests were conducted on the physical model. The tests controlled rainfall application and overland roadway runoff amounts and monitored outflow from the discharge pipe. The objectives were to increase the time to peak and reduce the peak discharge coming out of the pipe. The results were also used to calibrate a modified existing unsaturated two-dimensional groundwater flow code. After the code was calibrated, computer simulations were performed to determine the effects of storm size, rainfall distribution, constant rainfall application, media type, initial conditions, and the physical size of the ecology ditch. The simulations used 24-hour duration storm sizes of 0.64, 1.27, 2.54, 3.81, 5.08, and 6.35 cm (0.25 to 2.5 in.). Peak reduction was found to depend greatly on input hydrograph distribution and the ability of the soil to store water. In turn, the storage in the soil was found to be dependent on the intensities of the input hydrograph. The peak delay time for larger storms was quantifiable since it depended on the saturated hydraulic conductivity and the distance of the flow path. For larger storms, the ecology ditch managed a peak reduction in the range of 10 to 50%.