Hydrologic modeling of Low Impact Development systems at the urban catchment scale

In this paper, the implementation of Low Impact Development systems (LIDs) as source control solutions that contribute to restore the critical components of natural flow regimes, is analyzed at the urban catchment scale. The hydrologic response of a small urban catchment is investigated under different land use conversion scenarios including the installation of green roofs and permeable pavements. The modeling is undertaken using the EPA SWMM; the "do nothing" scenario is calibrated and validated based on field measurements while the LID control modules are calibrated and validated based on laboratory test measurements. The simulations are carried out by using as input the synthetic hyetographs derived for three different return periods (T= 2, 5 and 10. years). Modeling results confirm the effectiveness of LID solutions even for the design storm event (T= 10. years): in particular a minimum land use conversion area, corresponding to the Effective Impervious Area reduction of 5%, is required to obtain noticeable hydrologic benefits. The conversion scenario response is analyzed by using the peak flow reduction, the volume reduction and the hydrograph delay as hydrologic performance indexes. Findings of the present research show that the hydrologic performance linearly increases with increasing the EIA reduction percentages: at 36% EIA reduction (corresponding to the whole conversion of rooftops and parking lot areas), the peak and volume reductions rise till 0.45 and 0.23 respectively while the hydrograph delay increases till 0.19.