How do morphological characteristics of hillslope control water movement in the saturated and unsaturated zone
Résumé
Prediction of vegetation effect on soil moisture is a central feature of soil vegetation models. At hillslope scale, soil moisture is controlled by land use, soil characteristics, topography, stream and groundwater proximity etc. This paper aims to evaluate the importance of morphological characteristics on spatial soil water storage variation and their effect on water movement at hillslope scale. Five hillslopes were selected according to a set of morphological characteristics i.e. hillslope length, slope, drainage area, degree of convexity and concavity, convergence criteria, stream order. Soil characteristics and moisture were measured. Morphological characteristics were extracted from high resolution LIDAR. A physically-based, finite element model using Richards equation for variably saturated flow was implemented. Simulations were carried out for five hillslopes to evaluate the effect of morphological characteristics. Model sensitivity to soil hydrodynamic properties as well as hillslope morphology criteria was analyzed. Results obtained show that a spatial organization trend of morphological characteristics, especially soil thickness and porosity varies with topography and defines soil water capacity which seems to be a major factor on water availability for root uptake. The relationship between soil characteristics, hillslope morphology and water storage variation is a key to understand groundwater recharge amount control. Our results suggests a new perspective for the main morphological characteristics to consider for water movement modeling.