Physically based modeling of stormwater pipe leakage in an urban catchment

Abstract

In urban stormwater pipe networks, pipe leakage may lead to reduction of groundwater recharge, to significant reduction of groundwater levels, and to subsurface contamination. In the present study, stormwater pipe leakage is simulated in a case study representing an urban catchment using the coupled groundwater-pipe network flow model OGS-HE. This model includes pipe flow, variably saturated subsurface flow and exchange fluxes to and from leaky pipes. The study area is a typical northern German urban catchment with a stormwater pipe network which is located partly below and above groundwater. The successful calibration of a groundwater model is shown. Based on the calibrated groundwater model, stormwater pipe leakage for pipe networks of different ages and different pipe defect sizes is investigated for dry-weather flow conditions and rainfall conditions. It is shown that standard defects with a size of 10-4 m2 per m pipe can result in a groundwater infiltration into the leaky pipe network, which is in the order of annual groundwater recharge. The same standard defect size leads to a reduction of local groundwater levels by several meters. Rain events of increasing return period reduce groundwater infiltration into leaky pipes and increase stormwater exfiltration from leaky pipes, while the temporal distribution of a rain event has no effect on stormwater leakage.