Influence of rock fragments on the water retention and water percolation in a calcareous soil

The water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil. The available water content (AWC) has been calculated from these data. We have shown that when the rock fragments are neglected, the AWC can be overestimated by 39%. When we do not neglect their volume but when their hydraulic properties are not considered, the AWC can be underestimated by 34%. By using a reservoir model, we have also calculated the effect of rock fragments on water percolation to groundwater. Depending of the climatic characteristics of the year, the underestimation of percolation when we neglect the rock fragments can reach up to 14.9% and the overestimation when we neglect their hydraulic properties can be equal to 15.8%. These findings emphasise the role of the rock fragments on the water supply in stony soils. (C) 2003 Elsevier Science B.V. All rights reserved.