Hydrological response times in lowland urban catchments characterised by looped drainage systems

Hydrological response times are often used to characterise runoff processes. They provide information about temporal resolution of catchments responses, thus of the required measurement resolutions of in-situ sensors as well as spatial sensors like rainfall radars. The objective of this study was to characterise response times for urban catchments in lowland areas equipped with looped, combined sewer systems. Subcatchments size vary between 0.3 and 7.8 ha. The results show that variation in catchment area size can explain only a part of variation in lag times between the subcatchments. Pipe length per subcatchment explains variations in lag times to a similar, low degree. Comparison of lag time values for looped networks and constructed branched versions of the same networks shows that lag time values are influenced by flow between subcatchments in about half of the looped networks, especially during low flow conditions. This means that in looped systems subcatchment area per exit point varies during a storm event and lag time cannot be related to a single catchment characteristic.