EFFECTS OF CRUST AND CRACKS ON SIMULATED CATCHMENT DISCHARGE AND SOILLOSS

Sealing, crusting and cracking of crusts of the soil surface has been observed in many parts of the world in areas with sandy, silty and loa my soils. Sealing and crust formation occurs under the influence of ra in storm and drying weather, With prolonged drying, surface crusts mig ht crack, leading to complex situations with respect to infiltration a nd runoff generation. Cracking of crusted loamy soils appears to be a general process. This study aims to measure the hydraulic properties o f fully crusted and cracked-crusted areas and to evaluate the effects of these measurements on catchment discharge and soil loss in a loess region of the Netherlands, using the LISEM soil erosion model. Samples with minimum infiltration rates (fully crusted) and with maximum infi ltration rates (cracked-crusted surfaces) were taken from fields with bare soil or winter wheat and their soil hydraulic functions were meas ured, The results of these measurements were used as input in the LISE M soil erosion model, Simulations of discharge and soil loss were done for each of these two land-uses and for two rain events, Additionally , simulated discharge and soil loss under actual recorded land-use wer e calculated. In all cases, soils with no surface cracks produced high er figures for discharge and soil loss than those where 10% of the sur face crust was cracked, For a good interpretation of the results for s oil loss, the spatial distribution of cracked-crusted areas and fully crusted areas has to be investigated in detail. To deal with cracked-c rusted and fully crusted areas in simulation modelling, care has to be taken to accurately measure the soil physical functions representing the maximum and minimum infiltration rates. An assignment of these fun ctions to calculation grids has to be made. As the LISEM model is capa ble of assigning different soil physical functions to each calculation grid, an improved prediction of the soil physical behaviour of the ca tchment can be simulated.