| Xiliugou river basin lies in Ordos city,Inner Mongolia and belongs to the wind-water erosion crisscross region.It is one of the major rivers flowing into the Yellow River.All the reserches and experiments have been carried out in this river basin.The geographic information database,hydrological database and meteorological database have been established.According with the data,the characteristics of precipitation,runoff and sediment have been analyzed by positioning monitoring,simulation experiment,the "3S"technology and so on.According to the databases,the characteristics of land use and landscape pattern evolution have been analyzed,and the variation process of vegetation coverage has been expounds.Based on the above analysis,the relationships not only between rainfall and runoff,but also between rainfall and sediment are established.The rule of vegetation in runoff and sediment generations is elucidated according to the data got from field experiments.what's more,the influence of vegetation coverage on runoff generation mechanism is discussed.The main results are as follows:(1)Characteristics of land-use and landscape evolution in Xiliugou river basin have been analyzedLandscape types in Xiliugou watershed can be divided intograssland,woodland,farmland,villages,water and unused land.The grassland landscape is the matrix of the six landscape.The change rates of patch numbers and patch areas are analyzed.The results show that the patch stability of cultivated land,forest land and village is the highest,and the patch stability ofunused land is more stable than other landscape types.The transformation analysis of landscape types showed that the conversion of unused land,grassland and cultivated land was the most severe.These landscapes are greatly influenced by human activities.(2)The temporal and spatial variation rule of watershed vegetation have been illustrated.Using the remote sensing image data,remote sensing interpretation method using multi spectral,the situation of land surface vegetation changes analysis of watershed,vegetation Valley Xiliu in coverage(coverage of vegetation coverage(45%?60%),low vegetation coverage 25%?45%),accounting for about 93%of the total area of the watershed.From the development and change of view,low levels of coverage area of vegetation shows an increasing trend,while low levels of coverage area of vegetation significantly reduce the whole basin,vegetation coverage showed good occurrence trend.(3)Precipitation showed an increasing trend,the runoff decreases,but the rainfall runoff relationship without substantially changing.According to the datafrom 1960 year to 2013 year,Xiliu gully watershed rainfall runoff basic data,using the mathematical statistics method,analyzes the variation characteristics of rainfall runoff Xiliu gully watershed.Years of Xiliu gully watershed(1960-2013 years)the average precipitation is 261.8mm,the overall point of view,in twentieth Century since the 90's,the precipitation showed increasing trend,the average years of 5%more than offset.The runoff havereduced significantly since 2000,and the flood season runoff accounted for an increasing proportion of the total net flow low.The sediment has also decreased significantly since 2000,the average sediment during 2000 to 2010 is only 75%of the average value from 1960 to 2013.Through the different periods of rainfall-runoff relationship analysis found that,The rainfall-runoff relationship has a differences in different years,But it did not change as a function of the type,and runoff mechanism has not changed.(4)Revealing the possible changes under varying conditions of vegetation cover runoff mechanism.Artificial rainfall test observations under different vegetation coveraged conditions show that vegetation has increased the soil infiltration capacity,The higher the degree of vegetation cover,the larger soil moisture when runoff.Under conditions of light intensity(0.5mm/min),whether there are still bare slope area or covered by vegetation,The rainfall is only impact in the soil moisture of soil surface(0?10cm);When rainfall intensity is 1.0mm/min or so,rainfall can affect more than 20cm of soil moisture on bare slope,and vegetation coverage area can affect more than 50cm of soil moisture.Under different test conditions,Whether bare slope or around 30%of vegetation coverage,The soil saturation reached only 84.5%of its maximum when runoff and not reached saturation.The occurrence of the conditions on the mechanism of runoff viewed that,it is horton runoff and has no change.In the process of rainfall runoff generation,Higher vegetation coverage is,bigger the surface soil moisture variation coefficient is.The soil moisture variation coefficient increases,and the soil moisture exchange activities more briskly.After 20 minutes,the coefficient of variation of surface soil becomes small.This phenomenon shows that the infiltration mode changes.Runoff patterns also change.(5)The variation range of soil related index changes in wind water erosion crisscross region was determinedHorton and Philip infiltration formula simulation results show that in the water wind erosion crisscross region,the empirical value k of soil characteristics is from 0.02 to 0.17,and the range of soil a change is between 0.5 and 2.0. |
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