Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion for...Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion formation and development was investigated on the topo-sequence of three catchments(300-500 m slope length); and on agricultural fields(6 m and 14 m slope lengths) with different crop-tillage surfaces during erosive storms.Rill density and rill erosion rates were measured using rill cross section survey and close range digital photogrammetry. Rill formation and development was commonly observed on conditions where there is wider terrace spacing, concave slope shapes and unstable stone terraces on steep slopes. At field plot level, rill development was controlled by the distribution and abrupt change in the soil surface roughness and extent of slope length. At catchment scale, however, rill formation and development was controlled by landscape structures, and concavity and convexity of the slope. Greater rill cross sections and many small local rills were associated to the rougher soil surfaces. For instance, relative comparison of crop tillage practices have showed that faba-beantillage management was more susceptible to seasonal rill erosion followed by Teff and wheat tillage surfaces under no cover condition. Surface roughness and landscape structures played a net decreasing effect on the parallel rill network development. This implies that spatial and temporal variability of the rill prone areas was strongly associated with the nature and initial size of surface micro-topography or tillage roughness. Thus, it is necessary to account land management practices, detail micro-topographic surfaces and landscape structures for improved prediction of rill prone areas under complex topographic conditions. Application of both direct rill cross section survey and close range digital photogrammetric techniques could enhance field erosion assessment for practical soil conservation improvement.展开更多
The runoff coefficient (RC) is the ratio between the runoff and rainfall amounts and is scale dependent, which is due in part to the heterogeneity of watershed characteristics. This study quantified the spatial scale ...The runoff coefficient (RC) is the ratio between the runoff and rainfall amounts and is scale dependent, which is due in part to the heterogeneity of watershed characteristics. This study quantified the spatial scale effects on runoff using long-term rainfall-runoff data on runoff plots and small watersheds. Effect of spatial scale on RC was studied for 12 runoff plots (2m by 15m) and three small watersheds (113-477 ha) in the highlands of Ethiopia using a total of 4397 and 13,92515-day cumulative pairs of rainfall and runoff data at watershed and runoff plot scales, respectively. The observed average RC of runoff plots was extrapolated based on the extent of representation of a particular watershed in terms of slope, land use, cover and soil type. The weighted RC of plots was then compared with the observed RC of the watershed to determine a scale factor for extrapolation. A decrease in RC from plot to the watershed was observed in Anjeni and Andit Tid watersheds, while an increase in RC in Maybar watershed illustrates the role of specific watershed conditions in determining the scale effect. This, in turn, suggests that the variation in scale factor is not well explained by the difference in the area alone. The scale effect of runoff generation was better explained by extrapolating the RC based on the representation of different watershed characteristics. Thus, extrapolation exercises in runoff modeling and scaling efforts of soil and water conservation practices should consider the scale effect cautiously.展开更多
This study aimed to assess the influence of conservation practices (P) and cover management (C) on soil loss reduction by determining it at the scale of landscape units in 16 systematically selected watersheds. Focusi...This study aimed to assess the influence of conservation practices (P) and cover management (C) on soil loss reduction by determining it at the scale of landscape units in 16 systematically selected watersheds. Focusing on major land management practices implemented through free community labor mobilization, the assessment combined remote sensing techniques, field observation, and expert as well as local knowledge. The results show an average net decrement of 39% ( ± 19%) in the P factor value and 8.9%( ± 21%) in the C factor value after implementation of land management practices. P factor value re-duction is linked to a high area coverage of level structures, while increases in the P factor value are associated with poor quality of structures, inappropriate practices, and wide spacing between structures on steep slopes. C factor value reduction is observed in non-arable shrub- and bushland with enriched area closure, whereas increased C factor values are associated with open access grasslands and untreated croplands. The overall change in P and C factor values resulted in a 42% ( ± 28%) relative soil loss re-duction. The demonstrated approach makes it possible to assess spatial and temporal dynamics in the P and C erosion factors and to estimate spatially disaggregated changes in the P and C factor values. This can help to improve parameterization of inputs for erosion modelling and to assess their relative soil loss effect. The approach provides valuable feedback on watershed planning processes and supports informed decisions regarding the appropriate selection of land management practices.展开更多
基金the Austrian Academic Exchange Service (OAD) for financially supporting this study
文摘Application of simple and locally based erosion assessment methods that fit to the local condition is necessary to improve the performance and efficiency of soil conservation practices. In this study, rill erosion formation and development was investigated on the topo-sequence of three catchments(300-500 m slope length); and on agricultural fields(6 m and 14 m slope lengths) with different crop-tillage surfaces during erosive storms.Rill density and rill erosion rates were measured using rill cross section survey and close range digital photogrammetry. Rill formation and development was commonly observed on conditions where there is wider terrace spacing, concave slope shapes and unstable stone terraces on steep slopes. At field plot level, rill development was controlled by the distribution and abrupt change in the soil surface roughness and extent of slope length. At catchment scale, however, rill formation and development was controlled by landscape structures, and concavity and convexity of the slope. Greater rill cross sections and many small local rills were associated to the rougher soil surfaces. For instance, relative comparison of crop tillage practices have showed that faba-beantillage management was more susceptible to seasonal rill erosion followed by Teff and wheat tillage surfaces under no cover condition. Surface roughness and landscape structures played a net decreasing effect on the parallel rill network development. This implies that spatial and temporal variability of the rill prone areas was strongly associated with the nature and initial size of surface micro-topography or tillage roughness. Thus, it is necessary to account land management practices, detail micro-topographic surfaces and landscape structures for improved prediction of rill prone areas under complex topographic conditions. Application of both direct rill cross section survey and close range digital photogrammetric techniques could enhance field erosion assessment for practical soil conservation improvement.
文摘The runoff coefficient (RC) is the ratio between the runoff and rainfall amounts and is scale dependent, which is due in part to the heterogeneity of watershed characteristics. This study quantified the spatial scale effects on runoff using long-term rainfall-runoff data on runoff plots and small watersheds. Effect of spatial scale on RC was studied for 12 runoff plots (2m by 15m) and three small watersheds (113-477 ha) in the highlands of Ethiopia using a total of 4397 and 13,92515-day cumulative pairs of rainfall and runoff data at watershed and runoff plot scales, respectively. The observed average RC of runoff plots was extrapolated based on the extent of representation of a particular watershed in terms of slope, land use, cover and soil type. The weighted RC of plots was then compared with the observed RC of the watershed to determine a scale factor for extrapolation. A decrease in RC from plot to the watershed was observed in Anjeni and Andit Tid watersheds, while an increase in RC in Maybar watershed illustrates the role of specific watershed conditions in determining the scale effect. This, in turn, suggests that the variation in scale factor is not well explained by the difference in the area alone. The scale effect of runoff generation was better explained by extrapolating the RC based on the representation of different watershed characteristics. Thus, extrapolation exercises in runoff modeling and scaling efforts of soil and water conservation practices should consider the scale effect cautiously.
文摘This study aimed to assess the influence of conservation practices (P) and cover management (C) on soil loss reduction by determining it at the scale of landscape units in 16 systematically selected watersheds. Focusing on major land management practices implemented through free community labor mobilization, the assessment combined remote sensing techniques, field observation, and expert as well as local knowledge. The results show an average net decrement of 39% ( ± 19%) in the P factor value and 8.9%( ± 21%) in the C factor value after implementation of land management practices. P factor value re-duction is linked to a high area coverage of level structures, while increases in the P factor value are associated with poor quality of structures, inappropriate practices, and wide spacing between structures on steep slopes. C factor value reduction is observed in non-arable shrub- and bushland with enriched area closure, whereas increased C factor values are associated with open access grasslands and untreated croplands. The overall change in P and C factor values resulted in a 42% ( ± 28%) relative soil loss re-duction. The demonstrated approach makes it possible to assess spatial and temporal dynamics in the P and C erosion factors and to estimate spatially disaggregated changes in the P and C factor values. This can help to improve parameterization of inputs for erosion modelling and to assess their relative soil loss effect. The approach provides valuable feedback on watershed planning processes and supports informed decisions regarding the appropriate selection of land management practices.
