SOIL-WATER CONDITIONS AND FORECASTING RAIN WATER RUNOFF

The present work intends to show to what extent direct measurements of soil-moisture conditions, which up to now were not included in simulation processes, can improve discharge forecasting on a small catchment. In most storage models, it has been shown that because of an inadequate representation of the water yield function at the basin scale, the simulation of discharges was made difficult, particularly during transition periods. A comparison was drawn, based on a very simple model applied to the Orgeval catchment, between the classical method calculating with indirect methods the soil storage state and the proposed method which replaces these calculations by measurements of the soil-moisture conditions. The results of the comparison show the superiority of the second method, the first one being unable to translate completely the complex reality of the rainfall-runoff transformation processes. The results show the interest of including in a forecasting model a soil-moisture condition index which is measured locally at a small time-step during the hydrological cycle.