Study On Manning Resistant Coefficient And The Influence Factor In Diediegou Watershed

In the semi-arid area, water is the most important effect factor on vegetation of distribution pattern, community categories and species diversity. Forest vegetation on the oter hand can adjust water circulation, especially in slope runoff, Manning resistant coefficient (n) is one important parameter for describing the status of slope runoff, which influence runoff velocity and flux but is affected by fluctuant surface and the vegetation. To combine simulation test (on the slope of 14°, input flux is 10, 20, 30, 40, 60 ml·s^-1) and primary test (input flux is 60 ml·s^-1) , the Manning resistant coefficient (n) is measured in different forest vegetation and in different interface in order to discuss the effect mechanism of vegetation on slope hydrological process. The results are shown as below:1 .The test show that the mount of litter of Larix principis-rupprechtii can obviously obstruct the surface runoff, especially when it is more than 25.0 t·hm^-2, Compared with litter-removed treatment , the surface runoff velocity are redoed respectively 57.21% , 60.71% , 66.14% , 69.77% and 72.07% , when the input flux is 10, 20, 30, 40 and 60 ml·s^-1 . The relation about runoff velocity-reduced (ΔV) with the flow of unit width (q) and litter coverage (G) is expressed as ΔV = 3.6l77q^0.5075G^0.4315(R² =0.9102). It also find that the amount of litter 10 t·hm^-1 is an important value, for Manning resistant coefficient (n). It increase sharply when the amount over the point whereas increase slowly when below the point. The relationship between Manning resistant coefficient (n) and the amount of litter can expressed as n - 0.0154×G^0.3691(R² = 0.8607).2.Under stone coverage on slope, the form of surface runoff is unsticking flow, and the flow state is belonging to slow flow. When the stone coverage on slope adds, the surface runoff velocity will decrease gradually, on the other hand,the surface runoff velocity will decrease slowly when it over20%.Within the stone coverage of 10%⁴0% , the Manning resistant coefficient (n) change from 0.0121 to 0.0696 .3.Manning resistant coefficient (n) value range from 0.0117 to 0.2207 in 27 sample plots. The sequence (n) in different vegetation is Ostryopsis davidiana > meadow >Hippophaerhamnoides > Larix principis-rupprechtii.4.The relation coefficient of Manning resistant coefficient (n) with slope (/) surface roughness (Q and the soil bulk density (pb) (0-5 cm layer) is 0.627 , 0.552 , -0.444 , respectively . And the relation among them is showed as n = 0.2038x/ + 0.8006xC-0.0147x/?6 -0.091 (R2 = 0.439) .