Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2000
Publication Date: N/A
Citation: Interpretive Summary: Soil erosion data from very steep slopes are rare, and consequently our current knowledge of rates of soil loss on very steep slopes is very limited. In the United States we don't normally farm on very steep slopes, although such steep slopes do occur in special cases such as for strip mines or construction sites. In other parts of the world it is not uncommon to find hillslopes up to 60% with crops on them. One of those areas of the world is China, and in particular the Loess Plateau of China. In this study we were able to analyze soil erosion data from three sites on the Loess Plateau of China on slopes up to 60%. This data is very rare, and in fact, to our knowledge it is unique in the world in terms of the very high slopes under which it was collected. In a previous study we investigated the effects of slope steepness on erosion rates at high slopes using similar data from China. In this study we investigated the effect of fthe length of the slope on erosion on these very steep slopes. Our result indicate that the data follows the trend predicted by the USDA-Universal Soil Loss Equation (USLE) for slope length effects on erosion quite well. Interestingly, the newer USDA technology, the Revised Universal Soil Loss Equation, which is currently being adopted in the United States, does not follow our trends in measured data for slope length as well as does the USLE. The results of this study will assist soil conservationists, engineers, and land uses planners in making better soil erosion predictions for steep slopes.
Technical Abstract: Soil Erosion data from very steep slopes is rare, and consequently our current knowledge of rates of soil loss on very steep slopes, i.e., those in excess of approximately 25%, is based on theory rather than on data. Empirical soil erosion models continue to play an important role in soil conservation planning and environmental evaluations around the world. The effect of the length of the hillslope on soil loss, often termed the slope length factor, is one of the main and most variable components of an empirical model. The purpose of this study was to evaluate the relationship between soil loss and slope length for slopes up to 60% in steepness using the common relationship L=(y/22.1)*m, where L is normalized soil loss and y (m) is length of slope. Soil loss data from natural runoff plots at three locations on the loess plateau in China and some data presented previously by Wischmeier et al. (1958) were used. The results indicated that for the plots from China, the exponent, m, for the relationship between soil loss and the slope length from loess plateau was 0.44. For the data as a whole, the exponent did not increase as slope steepness increased from 20 to 60%. We also found that the value of m was greater for intense storms as compared to less intense storms. These experimental data indicate that the USLE exponent, m=0.5, is more appropriate for steep slopes than is the RUSLE exponent.