Zhenzhou Shen

Effects of landforms on the erosion rate in a small watershed by the 137Cs tracing method

Its very important to analyze and evaluate quantitatively the effects of landforms on soil erosion for the prevention and treatment of soil loss in a small watershed. The objective of this study was to evaluate the effects of landform factors on erosion rate by the (137)Cs tracing method in a small watershed in the Purple Hilly Area of China. The erosion rates under different slope lengths, slope gradients and slope aspects were estimated in Xiangshuitan watershed in the Purple Hilly Area in Sichuan Basin by the (137)Cs tracing method. The results showed that the erosion rate decreased exponentially with downslope distance, and it increased with increasing slope gradient during the scope of 5 degrees -16 degrees. The slope aspect had great impact on the erosion rate, and the hillside on the sunny slope had larger erosion rate than that on the shady slope, particularly for the farmland.

Using 137Cs to quantify the sediment delivery ratio in a small watershed

Understanding the sediment delivery ratio (SDR) is important in controlling sediments for the sustainable development of natural resources and in the design of the construction such as dams and reservoirs. The purpose of this investigation is to determine the SDR by the (137)Cs tracing method in a small watershed in the Sichuan Hilly Basin of China. In the study watershed, different land plots are divided according to the land use type, and 97 sampling sites were selected from these plots. The results show that the average net soil loss rates from the forest land and sloping cultivated land are 1759 and 4468t/km(2)a, respectively. No (137)Cs was detectable on the bare rock surfaces and previous work showed that the erosion rate from the bare rock area was 14,260t/km(2)a. In the depositional zone, the sedimentation rates in the Caoto (a kind of cultivated land located at the foot of hills) and paddy field are 3113 and 3562t/km(2)a, respectively. Combining the area of each land use in the small watershed, the SDR of 0.40 is obtained in the past four decades. The (137)Cs technique was shown to provide an effective and rapid means of estimating the SDR within the small watershed.

Driving force characteristic under different Land use ways slope

Analyzed the erosion characteristic on different rainfall and different underlying horizon in base of yellow river institute of hydraulic research at 2008. The date shows: the soil erosion amount of bare slope and arable slope is 100 times that of grass slope; the steady soil erosion amount of small rainfall is 1/4 times that of middle rainfall and is 1/30 times that of heavy rainfall on grass slope; the change of flow shear force at 90mm/h rainfall in different land use ways, when they get the fluctuate steady state, the flow shear force of bare slope and farmland is about 2000Pa, the flow shear force of 20%, 40%, 60%, 80% grass cover slope are 2/5, 3/10, 1/4, 1/5 times to 2000Pa. At the experiment condition, the corrosion resistance of soil is 5.89g/Pa.min-1, the critical flow shear force to cause rill erosion is 0.31Pa.