Effects of sustainable measures on runoff hydrograph in an urbanized drainage area

Urbanization changes characteristics of a drainage area and alters components of a natural hydrologic cycle. Runoff volumes increase, stormwater runs off more quickly and consequently peak flows become larger. Human alteration of the flow regime changes the natural pattern of hydrologic variation and disturbance, which may ultimately lead to river ecosystem degradation. For this reason an alternative stormwater management approach has been devised that mimics natural hydrologic functions by means of sustainable measures which manage rainfall where it falls. \ud This investigation uses a hydrological model to evaluate the effectiveness of different sustainable measures and their combinations in reducing runoff volumes and peak flows on a small drainage area which is representative for a wider city center of Ljubljana. We assumed these measures to be distributed across the drainage area having regard to the current legislation, spatial and technical constraints. The effects were studied for rainfall events of different return periods. Discharge measurements were made at the drainage area outflow and a rain gauge was situated in the vicinity of the study site.\ud In the case of events with a return period of 1 year or less, the runoff volumes and peak flows reduction was approximately 45 % in both cases, when simulating a combination of measures, involving infiltration shafts, pipe infiltration trench elements and green roofs. On the other hand, when simulating the same combination of sustainable measures for a 100 year event, the reduction of runoff volume and peak flow was only 12 % and 10 % respectively. We’ve arrived at a conclusion that sustainable measures are more effective in reducing runoff volumes and peak flows for smaller and more frequent rainfall events