Spatial analysis of hydraulic conductivity for slope deposits at catchment scale in Northern Tuscany, Italy

Hydraulic conductivity (K) is a relevant engineering geology property of slope deposits overlying the geological bedrock. This parameter is relevant at the field scale to simulate infiltration and runoff processes, hillslope stability numerical analysis, hydrological studies and environmental issues. Direct measurements (field and laboratory tests), as well as indirect estimations are available in the literature for evaluating K, the latter being based on factors such as grain size distribution, bulk density, organic matter, etc. Many measurements are required to obtain reliable estimations, particularly for slope deposits, where these factors are characterized by wide range of variation. Hence, values of K of slope deposits are often uncertain and their spatial variability is generally unknown. In order to face these issues, a wide set (about 750) of K field measurements has been performed in the vadose zone of slope deposits, within Northern Tuscany (Italy), by means of constant and/or falling head permeameter. For each test site (a total of 150 locations), also engineering geology properties of slope deposits have been determined, such as depth to bedrock, texture, bulk density, Atterberg limits and grain size distribution. The site variability of K has been estimated by statistical analysis, moreover geostatistical techniques have been applied to infer the spatial distribution at the catchment scale. The results show that K varies along the slope deposits profile and in the geographic neighborhood of the test site, also exhibiting high regional variability within the study area.