| Popis: |
Gully erosion is a geomorphic threshold phenomenon controlled by different environmental factors as well as human activities. In this research, we examined the effect of land use on hydraulic flow and the consequent head cut initiation for similar soil conditions using an experimental plot of 15m*0.4m. Results indicated that boundary shear stresses τcr for gully initiation in rangeland, dry farming and abandoned land are 192, 43 and 174, respectively, due to the differences in surface vegetation cover. Moreover, the dyne/cm2 turbulence of flow and soil response to an increase in water depth showed complicated behavior, which could be attributed to the effect of surface micro relief features and land use impacts. Compared to dry farming, the short vegetation cover in the rangeland decreased the effect of ground cover on flow regime. Even after seven years of abandonment, the response of agricultural land to increasing shear stress was similar to that of dry farming, which indicated the low resilience and high erosional susceptibility of soil in dry land was the environments. The main explanation for dramatic (3-4 fold) variations of τcr in dry vegetation cover and soil surface conditions. In fact, the remarkable decrease of τcr farming was related to the effect of tillage practice on soil susceptibility and aggregate used in some strength. The findings indicated that a critical shear stress of 35 dyne/cm2 physically based models for erosion prediction is not appropriate for estimating gully erosion. In addition, the duration of land abandonment has a crucial influence on soil erodibility that has been less considered in erosion models. |
