Linking clay enrichment and sediment delivery processes

Recent research has directed attention to the size distribution of eroded material because of its influence on deposition mechanics and in carrying capacity of pollutant materials. At first, in this paper the relationship between aggregate breakdown mechanism and erosion processes is briefly reviewed. Then the link between the clay enrichment ratio and the sediment delivery ratio at morphological unit scale is investigated. For 129 soil samples well distributed over the Sicilian Sparacia basin, the values for the experimental clay enrichment ratio calculated by the measured ultimate grain-size distributions are compared with the theoretical clay enrichment ratio values obtained by a procedure based on effective grain-size distribution. The clay content measurements, carried out in sediment samples drawn out from the sedimentation tank located at the basin outlet during the period February 1996-February 1997, are used to calculate the coefficient appearing in the relationship applied to estimate the sediment delivery ratio of each morphological unit. A relationship for estimating this coefficient using sediment clay content, measured by a conventional ultimate particle-size distribution, is also proposed. Finally, a Monte Carlo technique and caesium-137 measurements carried out in the experimental basin are used for verifying the accuracy of the sediment delivery distributed model which is strongly dependent on the estimate of the coefficient appearing in the sediment delivery ratio relationship. © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.