José-Frédéric Deroubaix

Rainwater harvesting to control stormwater runoff in suburban areas. An experimental case-study

On a 23 ha urban watershed, 10 km East of Paris, rainwater tanks have been installed on 1/3 of the private parcels to prevent stormwater sewer overflows. This paper investigates the macroscopic effect of rainwater harvesting on runoff, and thus the potential of this technique for stormwater source control. The analysis is performed using the SWMM 5 model, calibrated on rainfall- runoff measures from two measurement campaigns, before and after the equipment. The availability of two data-sets allows the authors to point out changes in the catchments behaviour. The main findings are that: (1) catchments evolution, mainly caused by individual land-cover modifications, produces non-stationarity of the hydrologic behaviour; (2) the rainwater tanks installed, although they affect the catchment hydrology for usual rain events, are too small and too few to prevent sewer overflows in the case of heavy rain events.

Linking the management of urban watersheds with the impacts on the receiving water bodies: the use of flow duration curves

There is growing evidence that changes in the current hydrological behaviour of urbanising catchments are a major source of impacts on the downstream water bodies. However, current flow-rates are rarely considered in studies on urban stormwater management, usually focused on extreme flow-rates. We argue that taking into account receiving water bodies is possible with relatively small modifications in current practices of urban stormwater modelling, through the use of Flow duration curves (FDCs). In this paper, we discuss advantages and requirements of the use of FDCs. Then, we present an example of application comparing source control regulations over an urbanised catchment (178 ha) in Nantes, France.