Analysis On The Sediment Reduction Effects And Its Change Process Of The Soil And Water Conservation Measures On Slopes In Dali River Watershed

Based on the theory of soil and water conservation,hydrology,landscape ecology,sediment dynamics and mathematical statistical,the sediment reduction mechanism as well as the change process of the sediment reduction effects by soil and water conservation measures on slopes in Dali river watershed was studied.Following conclusions were reached:(1)Determining the quanlity and quantity of main soil and water conservation measures on the slope.Based on data collection and typical investigation,combined with the RS imagine analysis and GIS Technologies,The dynamic process and change tendency of the quantity and quality of soil and water conservation measures on slopes in Dali river watershed was studied. There were 4.3 km~2 terrace land,35.21km~2 forestland and 4.51km~2 grasslands in Dali river watershed in 1956.Until 2002,area by soil and water conservation inceased a lot,and there were 217.93 km~2 terrace land,788.721km~2 forestland and 50.12km~2 grasslands in 2002.The harnessing areas of soil and water conservation rapidly increased.(2)Based on the simulating study and site-specific observation,mechanics of sediment reduction by shrub and herbaceous vegetation was analyzed.Results showed that the vegetation coverage degree,as well as the sediment yield characteristics on the slope varied with the vegetation types and seasons.And the sediment yield on the slope was deeply affected by the spatial structure and deposition model of the vegetations measures.High vegetation coverage degree has stronger function of soil and water conservation.(3)According to the further researches on the sediment reduction effects by the soil and water conservation measures on slope,the formula for the sediment reduction effects calculation was established in the flood season.In Dali river watershed,the results showed that the sediment reduction effects of the terrace land decreased when the rainfalls greater than 300mm in the flood season.The sediment reduction effects of the forestland was not significant when the vegetation coverage degree of forestland was less than 20%.The sediment reduction effects of the forestland had no remarkable change when the vegetation coverage degree of forestland was greater than 70%.The sediment reduction effects of the grassland had no remarkable change on grassland when the vegetation coverage degree of grassland was greater than 60%.(4)The sediment-reducing modulus of different grades of soil and water conservation measures on slope in Dali river watershed was calculated.By the observation data and plots experiment,combined with the mass analysis of the main soil and water conservation measures on slope,the sediment-reducing modulus were calculated as 1.55·10~4t/km~2,1.21·10~4t/km~2 and 1.12·10~4t/km~2 for theⅠterrace land,Ⅱterrace land andⅢterrace land.The sediment-reducing modulus were calculated as 1.38·10~4t/km~2,0.525·10~4t/km~2 and 0.225·10~4t/km~2 for theⅠforestland,Ⅱforestland andⅢforestland.And the sediment-reducing modulus were calculated as 1.32·10~4t/km~2,0.84·10~4t/km~2 and 0.63·10~t/km~2 for theⅠgrassland,Ⅱgrassland andⅢgrassland.(5)The sediment reduction amounts of soil and water conservation measures on slope were calculated in Dali river watershed.The sediment-reducing amounts of soil and water conservation measures on slope were calculated as 254.6·10~4t,549.2·10~4t and 948.6·10~4t for the year of 1970s,1980s and 1990s.The annual average sediment-reducing amounts of soil and water conservation measures was 724.2·10~4t during 1970～2002.The annual average sediment-reducing amounts of the terrace land,forestland and grassland was taken for 197.4·10~4t,513.9·10~4t and 12.9·10~4t.