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A new compact model coupling rainfall-runoff and routing model to support reservoir releases management

IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Author(s): Simon Munier
Julien Lerat
Gilles Belaud
Xavier Litrico
S. Munier : Cemagref, UMR G-EAU, 361 rue J.F. Breton, BP 5095, 34196 MONTPELLIER cedex 5, FRANCE, Tel: +33 4 67 04 63 50, Fax: +33 4 67 16 64 40, email: simon.munier@cemagref.fr J. Lerat : Cemagref, Parc de Tourvoie, BP 44, 92163 Antony cedex, FRANCE,

Keyword(s): flow routing, rainfall-runoff, compact model

AbstractMany reservoirs have to release water in order to simultaneously satisfy withdrawals along a river reach and guarantee flow at certain critical points. When these points are distant from the reservoir, the managers must account for the transfer time as well as the possible contributions of the catchment area. For the design of real time regulation tools, it is necessary to elaborate compact models for the flow routing so as to predict the behavior of the river during various events (dam release for example). However this transfer can be influenced by lateral inflows, in particular the contributions due to the rainfall, which are generally neglected in the existing routing methods. The purpose of this paper is to establish a compact model of flow routing integrating the contributions due to the rainfalls. This model will result from the coupling of a flow routing model and a rainfall-runoff model. The flow routing model is a physical model, based on the linearized Saint-Venant equations transposed in the Laplace domain. The downstream discharge is then expressed analytically with respect to the upstream discharge (dam release), and to lateral inflows distributed along the river reach. The lateral inflows result from a rainfall-runoff model applied to the catchment area, which is divided into sub-basins whose runoff ends in a point of the principal river. The flow resulting from the rainfall-runoff model is then distributed between the sub-basins according to their respective surfaces, and is introduced into the river in the form of lateral inflow located at each sub-basin mouth. In that way, the flow routing model takes the catchment contributions into account. The integrated model is applied to a catchment area presenting a dam at the upstream end, a set point (reserved flow) at the downstream and intermediate tributaries. The parameters of the flow routing model are first identified from an event without lateral inflow. One deduces from it the characteristics of the river reach, and the transfer function of the lateral inflow. The parameters of the rainfall- runoff model are given in a second identification step on a rainy event. The integrated model is finally validated on another event. This method provides a simplified flow routing model in a river reach integrating the contributions due to the rainfall. These inflows can contribute significantly to the flow dynamics. With this method, it possible to identify the model parameters from the knowledge of the upstream and downstream discharges and of the rainfall on the catchment area. This model will be used in a later phase to determine the dam release to be carried out for the management during the low flow periods of the catchment area.
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