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Discharge transposition between catchments through a geomorphology- based deconvolution–reconvolution approach

Congress: 2008
Author(s): Houda Boudhraâ, Christophe Cudennec, Mohamed Slimani
Houda Boudhraâ(1,2), Christophe Cudennec(3), Mohamed Slimani(1) 1 INAT, Lab. STE, 43 Av Charles Nicolle, 1082 Tunis Mahrajène, Tunisia boudhraa_hda@yahoo.fr 2 IRD, UMR G-EAU, Tunis, Tunisia 3 INRA, Agrocampus Rennes, UMR SAS, Rennes, France

Keyword(s): Deconvolution-reconvolution, geomorphology-based transfer function, net rainfall, transposition, ungauged basin.
AbstractThe geomorphological structure of hydrological paths can be observed for any basin, from information –of various kinds and qualities– about relief and watercourses. Moreover it can be translated into basin-level transfer functions, through more or less complex conceptualisations, according to the available data and knowledge. In data-scarce contexts, including in ungauged basins, the use of geomorphology- based transfer functions is a strong perspective, provided that the net rainfall coupling variable at the hillslope–river network interface is assessed. The aim of this study is to consider couples of basins and their respective non- calibrated robust geomorphology-based transfer functions. In the frame of discharge transposition, the two basins are respectively considered as the provider and the receiver. A discharge series of the provider basin is deconvoluted through the inversion of its transfer function, to assess the net rainfall series. Assuming, as a first step, homogeneity between the two basins, the assessed net rainfall series is considered to be relevant for the receiver basin and convoluted with its own transfer function to simulate the discharge series at its outlet. Optimistically, homogeneity between basins could be sufficient enough for nested, neighbouring and similar basins to make this approach promising when the receiver basin is ungauged. The approach is tested with a set of four basins of semi-arid Central Tunisia (192, 180, 18.1 and 3.16 km²). Artificial events with spatially homogeneous rainfall input are built and considered in order to simplify the issue of semiarid spatio-temporal variability at this first stage. Each basin is alternately considered as the provider basin towards all three others. Transposed discharge series are compared to the reference framework. Transposed series appear to fit reference series very well, especially when the shape of the net rainfall graph is unimodal. For the four considered basins, transposition performs correctly in terms of timing, volumes and shapes of hydrographs. The basin scale seems to be influent when series are transposed from a larger basin to a smaller one. An uncertainty test is furthermore proposed by introducing an error dose to the net rainfall, which mimics a real uncertainty on rainfall variability.
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