Research On Benefit Of Runoff And Sediment Reduction Of Soil And Water Conservation In The Upper Reaches Of Hantaichuan Watershed

The upper reaches of Hantaichuan Watershed belongs to the first sub-region of loess hilly and gully region, its typical for soil and water conservation, this paper takes the upper reaches of Hantaichuan Watershed as the research area. Firstly, By understanding it’s present situation of land use, the management present situation of soil and water conservation and the characteristic of water and sediment in watershed comprehensively. Secondly, Set up the standard runoff plot experiment observation to determine the different land use types’runoff depth and erosion modulus. Thirdly, Based on the research of water storage, deposited sediment and the service life of typical check dams. then used "soil conservation method" to calculate the the benefit of water and sediment reduction of soil and water conservation measures of the upper reaches of Hantaichuan Watershed in 1998, 2013, used the "hydrology method" to calculate the benefits of water and sediment reduction of soil and water conservation measures from 1990 to 1999, from 2000 to 2010 at the same time. contrast analyzed the two methods’ results of water and sediment reduction. the following are main conclusions:(1) The annual rainfall amount change of Hantaichuan watershed is bigger, more than 70%of the annual rainfall is seasonal rains. Runoff has a high concentration of sediment, the runoff and sediment discharge annual difference is great, reduced obviously recently, and it distributes unequally in a year.(2) The runoff depth and erosion modulus of different land use types in 2013 changing trend consistently, it shows that: wasteland>closed forest> grass-planting>economic forest> arbor forest> shrubbery>mixed forest of arbor and shrubbery, the wasteland’s runoff depth, erosion modulus are biggest,10.7 mm and 8279 t/km2a separately, the mixed forest of arbor and shrubbery’s runoff depth, erosion modulus are smallest, they are 4.5 mm and 2696 t/km2 a separately.(3) The key dam which were built in 1980-1989 of the upper reaches of Hantaichuan Watershed service life is 26 years, longer than designed for 6 years. The key dam which were built in 1990-1999 service life 30 years, longer than designed for 10 years. The key dam, medium-sized dam and small-sized dam which were built in 2000-2009 service life is 34 years,20 years and 11 years separately, longer than designed for 14 years,10 years and 6 years separately. The key dam, medium-sized dam which were built in after 2010 service life is 36 years and 22 years separately, longer than designed for 16 and 12 years separately.(4) Based on "soil conservation method" to calculate the benefit of water and sediment reduction of soil and water conservation measures in the upper reaches of Hantaichuan Watershed in 1998,2013 was 835700 m3 and 2.152 million m3, the benefit of water reducing is 13.90% and 35.81% respectively. Amount of sediment reduction is 768600 t and 1.9077 million t, the benefit of sediment reduction is 16.40% and 40.71% respectively.(5) Based on the "hydrologic method" to calculate the benefits of water and sediment reduction of soil and water conservation measures from 1990 to 1999, from 2000 to 2010 is 1.82 million m3,8.51 million m3 respectively, the amount of sediment reduction is 2.43 million t,3.64 million t. water reducing were 13.07%,61.09% respectively, the benefit of sediment reduction is 60.45% and 60.45% respectively.(6) The calculation results of " soil conservation method" and " hydrology method" are contrasted, the distinction of this wo methods are indicated.The two methods both should be used to support each other in the future’s studies.