Drainage hydrology in the marshlands of western France

Flux prediction for drained fields can be obtained from convolution of a unit hydrograph with effective rain. The latter is calculated using a reservoir model, whose only parameter is the reduction coefficient of PET applied to gross rainfall. The transfer coefficient is calculated by two convolution methods, projection and multiple linear regression under constraints. The model is applied to data obtained from drained plots in the marshlands of Western France, which are flat and lying at sea level. Since in wet winter periods natural drainage is insufficient for crop production, some farmers lower the water level by pumping. In 5 plots ranging from 18 to 48 hectares, the evacuated flow was measured at the pump together with rainfall and PET. Results are used to fit the reservoir parameter of the model. Although the model is purely stochastic, the results obtained can be interpreted in terms of the permeability of the plot and the type of drainage.