Fabrice Rodriguez

Surface runoff in urban catchments: morphological identification of unit hydrographs from urban databanks

In this study, Urban Unit Hydrographs (URBS-UHs), are derived from the analysis of an urban databank for three urban catchments with surface areas ranging from 18 to 180 ha. The geometry of property lots, streets and sewer networks allows for an explicit description of the runoff production areas and their downstream flow channels. The Mannings equation is used to compute the flow velocity along the identified channels under rainfall intensities that we related, for purposes of convenience, to return periods. The shape and the scale of the URBS-UH are primarily influenced by catchment morphology, channel roughness and rainfall return period. As a consequence, the transfer function is not unique but rather depends on rainfall characteristics. The URBS-UHs identified without any parameter calibration are encouragingly similar in shape and scale to the unit hydrographs derived from rainfall-runoff measurements over the three studied urban catchments.

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.

Manhole cover detection using a geometrical filter on very high resolution aerial and satellite images

One of the direct consequences of urban growth is the multiplication of buried utility networks. It is difficult to obtain complete and accurate maps of these networks because they have often been produced by different parties at different times. This work aims at putting forward a methodology to detect manhole covers on high resolution images, in order to reconstruct an urban drainage network. A circular detection filter is applied to high resolution orthophotos and Pléiade images to pinpoint mahole covers. The primary results are encouraging as 42% of manhole covers are detected by this method. Further work is carried out to improve the method and extend it to rectangular grates, that are not detected by the circular filter.