| The Loess plateau of China was the world’s most serious water and soil losses areas, asthe most primary gully control measures in the Loess plateau, check dams plays atremendous role in the soil and water conservation. There were about90thousands checkdams in the Loess plateau by the end of2008, according to the plan, the amount of checkdam will reach163thousands by the end of2020. So big check dams construction, mayhave as profound an impact on the ecology environment of the Loess Plateau. Therefore,thoroughly and systematically study on environmental impact of check dams, to promotethe development of soil and water conservation in loess plateau, expand soil and waterconservation science research, has played an active role. This paper was base on the theoryof geography, hydrology, ecology and soil and water conservation, to employ remotesensing, stable isotope, soil erosion prediction model technology, check dam effecting thevegetation features, hydrologic cycle, erosion process are analysed comprehensively. Themain conclusions were as follows:(1) Gully control engineering change the Surface water cycle process was veryremarkable. To reveal evaportranspiration characteristics of watersheds different inadoption of water and soil conservation measures, two watersheds, Jiuyuangou andPeijiamao were selected as subjects for estimation of evapotranspiration from differentunderlying surfaces using the energy-balance based SEBAL remote-sensing model. Resultsshow that the daily evaportranspiration of Jiuyuangou, which is better managed in waterand soil lands different in land use followed the order of check dam> orchard> woodland> grassland> terrace> slope land in daily evaportranspiration. The different land use soilmoisture content analysis shows that: after rain, soil surface moisture of terrace andslopelands was degrade slowly, unlike returning terrace and slope farmland, there weredegrade quickly. Check dam moisture vertical variable ratio more than other land use type,the largest moisture vertical variable ratio reached52%, which appeared at70cm~80cm, and in the depth of80cm~130cm, have obvious layered; Based on the observational dataof precipitation and runoff from1958to1969, analysed the impact of check dam on runoffcoefficient and basin lag time. the runoff coefficient of Jiuyuangou is29.43less thanPeijiamao, Wangmaogou is34.63%less than Lijiazhai, Xiangtagou is16.78%less thanTuanyaungou. The basin lag time of Wangmaoogu more than tripled Lijiazhai.(2) Analysis of the gully engineering measures (check dam) to the influence of thewatershed vegetation. Gully engineering measures can increase the local vegetationfraction and the diversity of plant communities within a small range. The NDVI of thewatershed under different water and soil conservation managements displayed differentseasonal variation. In July, NDVI of Peijiamao concentrated distribution in between0.3and0.4, followed by between0.2and0.3, and the range was60.98%. In Jiuyuangou, therange was only25.79%.(3) The effect of the sediment interception of check dams is very significant. Modulus ofsediment yield was calculated by observed data from1958to1969show that: Modulus ofsediment yield of Jiuyuangou is28.09%less than Peijiamao, Wangmaogou is67.75%lessthan Lijiazhai, Xiangtagou is27.75%less than Tuanyaungou. Based on the analysis of aheavy rain process in7-17-2012, in this heavy rainfall,159031t sediment is deposit in the23chaeck dams of Wangmaogou, Wangmaogou hydrologic station sediment discharge is27891t, total of erosion amount is186922t, the soil erosion modulus of Wangmaogou is31310t/km~2in this heavy rainfall, the sediment delivery ratio is0.15.(4) Quantitatively analyzes the charge of soil erosion modulus along with the increase insiltation height. To study the influences of check-dam siltation on soil erosion of awatershed, we built a simplified watershed model for the Loess Plateau hilly-gully regionincluding terraced fields, slope farmlands, steep-slope grasslands, and dam farmlands, anddefined three states of watershed (i.e., pioneer, intermediate, and climax stages,respectively). Then, the watershed soil erosion moduli at various stages were studied byusing a revised universal soil loss equation. Our results show that the pioneer and climaxstages are the extreme states of watershed soil-and-water conservation and control; in thepioneer stage, the soil erosion modulus was184.43t×ha-1×a-1; in the climax stage, the soilerosion modulus was4.62t×ha-1×a-1; in the intermediate stage, the soil erosion modulus (y)below the edge of gully exhibited a linear decline along with the increase in siltation height (x), the expression is y=-1.5315x+121.15, intercept b was the increase in reference erosionmodulus, a was the erosion reduction rate, both of which increased with the upwardmovement of the edge of gully.(5) This paper presented a new concept-erosion control degree, which can estimate thedegree of soil erosion controlling. The minimum possible soil erosion moduli (2573t/(km~2×a)) under capacity of soil and water conservation measures in Wangmaogouwatershed was calculated. Use2004land use map, calculates the actual soil erosion moduliof Wangmaogou is7413t/(km~2×a), and defined erosion control degree is the minimumpossible soil erosion moduli divide the actual soil erosion moduli, the erosion controldegree of Wangmaogou is0.35, at a lower level, due to existed a number of slopingfarmland and forestry area is less. We suggest that erosion control degree as the evaluationindicator about soil and water conservation of the status quo. |
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