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Optimal raingauge network design using geostatistics and Simulated Annealing

Congress: 2008
Author(s): Maria Da Cunha2, Zoubeida KEBAILI BARGAOUI3
2 Civil Engineering Department University of Coimbra Polo II da Universidade-Pinhal de Marrocos 3030-290 Coimbra Portugal. e-mail : 3 Ecole Nationale d’Ingénieurs de Tunis, Laboratoire de Modélisation en Hydraulique et Environnement,

Keyword(s): maximum rainfall intensity, index of erosion, scale duration, variance, kriging, external drift, Simulated Annealing, optimal network design
AbstractFor design of water management and road structures as well as for flood management and soil protection in regard to erosion, it is often operated with the maximum intensity over a time of reference. Two approaches of optimization of raingauge network were proposed and implemented. These approaches take account of two objectives. The first objective is the minimization of the variance of the estimation of the spatial variability of maximum intensity of rainfall for a giving duration. The second problem aims at minimizing the variance of estimation of the erosive character of a storm event. In both cases, the problem consists of minimising an objective function which includes the accuracy of the areal mean estimation (as expressed by the kriging variance of estimation). To this purpose, kriging with external drift ED is adopted while the site altitude is taken as ED. The well known geostatistical variance-reduction method is used in combination with simulated annealing as an algorithm of minimisation. In both cases, the methodology is based on an extreme event and is aiming only on optimal augmentation of the previously existing network because of its low density. Choose of the scale duration obeys to hydrological considerations: a one -hour duration scale is adopted, which seems an adequate scale in regard to the hydrograph response of mid-scale watersheds (up to 400 km²). In order to develop the two problems, an extreme event is studied: the extreme event of Marsh 1973 in the North part of Tunisia. The intensities in the Marsh 1973 event were relatively small (locally up to 22 mm/h in 15 minutes) but were related to strong durations. This event led to very high rainfall amounts at large scale. The existing raingage network is consisting of thirteen instantaneous rain gauges, six belong to the Medjerda basin while the others are surrounding stations. The areas of reinforcement of the pluviograph network were defined for the two objectives (of estimation of the intensities of a storm event and the index of erosion of the same event) in an independent way. But the results are complementary.
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