| Vegetation is one of the key control measures of soil and water loss.The vegetation cover is the tradition indictor for measuring the soil and water conversion effects of vegetation.However,a lot of research results indicated that the vegetation pattern was also a key factor which affects the soil and water cionversion.It has Egreat significance to study the effect of vegetation cover and vegetation partern on conrtrolling the soil and water loss under the ecological construction of the Grain for Green on Loess Plateau.According to the inter-disciplinary theories such as geomorphology,landscape ecology,hydrology,soil and water conservation,by using the spatial analysis technologies and fractal tlheory,the effect mechanism of vegetation pattern on the procyess of erosion and sediment yield of slope-gully system and watershed in the paper.Firstly,the dynamic regulation mechanism of vegetation pattern on erosion dynamic power of slope-gully system was revealed through the indoor simulation rainfall experiment.Secondly,the arithmetic and calculation model of fractal dimension,such as box dimension,fractre surface dimension and fractal brown motion dimension were improved.A quantitative models of vegetation spatial pattern will be established to explain the response characteristic between the fractal dimension of the vegetation distribution and the sediment yield based on digital vegetation model;thirdly,a calculation method of the runoff erosion power based on energy of the event rainfall was developed.Lastly,a model was built based on spatial distribution characteristic of vegetation on erosion and quantitative parameters of vegetation distribution.The main results are listed as follows.(1)Vegetation patterns change the processes of water erosion.The order of benefit of water reception and sediment yield reduction of different vegetation patterns is middle and lower part of slope>lower part of slope>middle and upper part of slope>upper part of the slope,successively,which means under this experimental condition,the grass strips planted at a distance of 4m from slope are best effect,which can reduce water 7.4%and sediment yield 62.9%;with the continuation of rainfalls,the peaks of runoff and sediment yield are increase and decrease gradually,respectively;the initial time of runoff generation and peak gradually advanced;the stabilized time of runoff gradually shortened;the averages of runoff of second and third rainfall increased 5.4%～37.2%and 1.8%～21.8%respectively;the averages of sediment yield decreased 42.1%～82.5%,72.3%～92.3%,respectively,the initial times of runoff generation advanced 0.5～12.5min,1.9～8.0min,respectively,compared with the first rainfall;Vegetation on runoff reduction is in the range of about 5.0%,which can indicate the weaker effect on water conservation,comparatively,the sediment blocking effect is relatively better,which can make the sediment yield decrease about 33.0%.(2)Reveal the regulation mechanisms of soil erosion dynamic of vegetation patterns on the slope-gully system.Vegetation reduce soil detachment capability by reducing runoff shearing force τ;minimizing runoff degrees of runoff shearing force τ are quite different under different vegetation patterns;runoff shearing force of slope surface increases first and then decreases with increase of the distance between grass stripe and slope top;the runoff shearing force becomes minimum when the distances between grass stripe and slope top are 2m and 6m.the unite runoff power increases first and then decreases with increase of the distance between grass stripe and slope top,also,however the vegetation patterns have a little effect on unit runoff power.Runoff energy on slope surface of slope-gully system substantially unchanged,while a sharp rise of runoff energy consumption when get into the channel,which is in a tendency of increase first and then decreases,the runoff energy consumption of channel is 2.69 times larger than the slope.(3)Quantitative model of vegetation patterns of drainage area was improved based on fractal theory,and the related software was developed,also.NDVI and VC datasets of vegetation coverage of study area were reconstruction based on the maximum value synthesis.The arithmetic and calculation model of fractal dimension,such as box dimension,fracture surface dimension and fractal brown motion dimension was improved;fractal dimension calculation software of vegetation patterns of drainage area was developed,therefore the quantification of the spatial distribution of the drainage area was realized.The vegetation distributions in Dali River basin and its upstream Qingyangchabasin,the midstream Xiaoli River basin and downstream Chabagou basin show a better fractal characteristics in their unscaled interval;the FBM dimension index can serve as the quantitative indicators of characterization of the vegetation distribution pattern of drainage area.(4)Runoff-Sediment yield of Dali River was studied,which show a decrease tendency,while the rainfall have on decrease tendency.Using the reserved Universal Soil Loss Equation(RUSLE),the average erosion modulus of Dali River were 14960.11,20444.67,21290.22,11762.96,18638.51 t/km2·a,in 1985,1996,2000,2005,2010 years,respectively,which changed between the very severe and severe erosion,average erosion modulus became maximum in 2000;the slight erosion areas mainly distribute along the river side and upper stream,while the severe and very severe erosion are widely distributed,meanwhile with the increase of years,the ratio of very severe erosion area was increased from 32.6%to 45.8%.Yearly rainfall was tested by M-K test,which showed little changes in Dali River,no significant increase or decrease tendency;Runoff and sediment yield of each hydrological stations shows a significantly decreasing trend on the whole,while the runoff showed a clear downward trend,in which,sediment yield of Lijiahe and Suide station are only 86.3%,74.2%in 2000-2010 years corresponding with annual average,respectively.(5)The regular pattern of a number of spatial and temporal scales relativity of runoff erosion power and erosion model of drainage area was clarified.Based on the characteristics of flood energy calculation,trunoff erosion power based on different time scales was developed,which realized in different spatial scales,runoff erosion power can be calculated and analyzed monthly and yearly.Compared with runoff,runoff erosion power have a better correlation coefficient with sediment transport modulus.The correlation coefficient was improved from 0.64 to 0.91,which improved the accuracy of the calculation results.(6)Based on different spatial scale,the response model of vegetation patterns fractal quantization parameter and erosion power factor,was established initially.Taking the Loess Plateau Dali River as example,nonlinear mathematical model of the erosion and sediment yield of the establishment was established,and by employing the default factor test method,selected the Fractal Brownian Motion dimension of vegetation patterns,as vegetation landscape fractal dimension quantitative parameters.The studies show that,introduced by the fractal pattern of quantitative parameters and erosion dynamic indicators has higher precision,which can quantitatively descript coupling relationship between water and sediment of drainage area.The sensitivity of the effect of the runoff power on the sediment of basin is related to the vegetation pattern.The establishment of model and the proposition of method have a certain rationality and reliability,which can be referred by other sediment yield models. |
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