| Zhifanggou watershed of Pingliang located in the gully area of Longdong loess plateau. This watershed was listed as key management area and experimental base of Yellow River Basin by Yellow River Conservancy Commission and Soil and Water Conservation Committee since1954, and set up ten hydrology and rainfall observation station which formed the small watershed hydrological and meteorological observation station network and took an observation of rainfall evaporation, runoff,flood and sediment of the watershed for50years. With the implementation of the integrated management practice since1954, especially in twentieth century since the eighty’s, strengthen the comprehensive management of engineering and agricultural and biological measures, and carry out a test and demonstration, the vegetation coverage rate and the integrated management level of the watershed had great improvement. This article implement the investigation and experimental observation of the this watershed, by means of remote sensing and summary of large amounts of data, and base on analysis model based on the effect of soil erosion, gets the conclusion as follows:(1) Through the soil erosion data analysis, the changing law of double cumulative curve of rainfall-runoff, rainfall erosivity-sediment have general accord, and the variation tendency of the single cumulative curve of runoff-sediment have general accord, the time1986is a cut-off point, the distribution of soil erosion before1986have an obvious difference than after, and there are two soil erosion pattern in Zhifanggou watershed between1981-1997. Runoff is rapid growth with the rainfall increase in the period of earlier stage of governance and slower growth with the rainfall increase in the period of later stage. Governance measures and vegetation change have more obvious effect on the runoff and sediment transport.(2) This paper has chosen Zhifanggou watershed of Pingliang as study region, and chosen the rainfall date between the year1981and2004, LANDSAT TM imagery in2000,2005and2010, terrain data and soil chemical analysis data as basic date. By using of GIS, RUSLE Model and MPSIAC Model gave a quantitative estimation to the amount of soil erosion, and classified the soil erosion intensity in accordance with the "water erosion intensity classification standard". The factors of RUSLE Model included rainfall erosivity, soil erodibility, slope length and slope steepness factors, vegetation cover management factor and tillage measure factor, and the factors of MPSIAC Model included surface geology, soil, climate, runoff, topography factors, land cover, land use factors and upland erosion, channel erosion factors. According to each factor calculation method get the corresponding factor value, and the raster map and factor score. According to the two kinds of model calculate the modulus of soil erosion and sediment yield of the study area.①According to the analysis and calculation of factor of the two model and relative standards, under the RUSLE model, the main erosion of the three period of the Zhifanggou watershed is tiny erosion and light erosion, and the moderate erosion is less. The area of tiny erosion is increasing state, and the area of the other erosion is decreasing state, this phenomenon shows that the total erosion intensity in Zhifanggou watershed is into small, erosion intensity are transformed to a smaller level, in the analysis of results in2010, the serious erosion and mighty erosion disappeared, this shows that the implementation of comprehensive harness of soil and water conservation of Zhifanggou watershed achieved remarkable effect, and effectively alleviate soil erosion status.②Under the MPSIAC model, the annual sediment yield are mainly low sediment and moderate sediment in2005, and the serious sediment is less.(3) The soil erosion intensity of the area among different land use types are significant difference, and the main soil erosion intensity of terrace field, sloping cultivated land and buildings is tiny erosion intensity, this is because the cultivated land and construction land have water and soil conservation measures. The main soil erosion intensity of and grasses is moderate and tiny erosion intensity respectively, this is because the forests are scattered distribution, and lack artificial protection measures, so the erosion intensity is sharp. The soil erosion intensity of difficult using land is large because of the surface without vegetation and land use hard. When the other conditions remain unchanged, soil erosion increase with the increase of slope on slope in0-15°range, and the change is obvious, the change of the slope on soil erosion change little strength distribution on slope more than15°.(4) Each factor in RUSLE model is easy to obtain and has a high accuracy. So this model has a high adaptability. It is calculated by RUSLE model that average erosion modulus of the area in2000,2005and2010is1223.8t/(km2·a),1118.0t/(km2·a) and874,9t/(km2·a)respectively, and soil loss of the area in2000,2005and2010is23129.8t/a,21130.20t/a and16535.61t/a respectively. The measured average erosion modulus of the area in2000and2005is1580.5t/(km2-a) and1376.8t/(km2-a) respectively, and the measured soil loss of the area is29871.5t/a and26021.5t/a respectively, and the numerical results are basically consistent with the measured values. The amount of soil erosion in2005were reduced by8.6%,12.9%respectively more than in2000, and the decrement is also basically consistent, it can be considered that the RUSLE model can reflect condition of the soil erosion better in area. As for MPSIAC model, the measured sediment yield in2005is26021.5t/a, and sediment yield calculated by MPSIAC model is2136t/a, due to more analysis factors and the insufficient basic data, the model factor values are affected that even eventually lead to a big difference between simulation value and actual value. Comprehensive analysis, RUSLE model is suitable for quantitative analysis of soil erosion in the watershed. |
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