| In recent years,with the rapid development of social economy in Qinjiang river,the land use and land cover have changed dramatically.As the important headwaters of agricultural and industrial production in Lingshan county and the north and south area of Qinzhou city,the ecological environment of Qinjiang river has important effects on the areas along the river.An impertinent land use structure will lead to the water unbalance of qinjiang basin and the ecological environmental issues like soil erosion and land deterioration will follow.So,in support of GIS technology,some data of DEM,land utilization,soil type map and climate hydrology are used in this paper to build Qinjiang River SWAT distributed hydrological model.In the basis of analyzing the land use cover changes of the river in 1990 and 2008,Keep all elements the same,simulated the process of sediment and runoff under the different land use scenarios in 1990 and 2008.Furthermore,different land use scenarios were set up to further and quantificationally analyze how much the river runoff and sediment has been influenced by different land use construction.The results are as follows.(1)The SWAT distributed hydrological model of Qinjiang River was successfully established in this study and divide,the whole river into 44 sub-basins and 355 hydrologic response units.According to the results of sensitivity analysis,it used the observed data of runoff and sediment to calibrate and validate the model,showing the correlation coefficient R~2 exceed 0.9,Nash-Suttcliffe coefficient exceed 0.8 and the the runoff-sediment-yield volume showed the same change trend.Simulation precision of the model was high,distributed hydrological model was applicable to Qinjiang river.(2)The main types of land use in Qinjiang river are arable land,woodland and grassland,the area of three land use types account for the total area of more than90%.There were varying degrees of increase and decrease in land use types from1990 to 2008.With the transfer matrix,the outcomes show that the positive transfer area of Qinjiang river basin is 23.59 km2,and the negative transfer is 28.12 km2.The vegetation fraction in basin showed a downward trend.(3)Put the land use of 2008 into the calibrated SWAT model,and simulated the sediment and runoff in Qinjiang river from 1990 to 2008.Compared with the situation in 1990,the total of sediment and runoff under the land use scenarios in 2008 increased in all.it shows that the land use construction change is the main factor to in influence hydrologic effect in Qinjiang river.(4)On the basis of land use in 1990,7 kinds of land use scenarios were set up by diminishing vegetation fraction to simulate the runoff and sediment.The result shows that,when the percentage of forest cover is raised to 53.7% in the scenario of future land use,the intensive of construction land and the river runoff and sediment will reach the minimum,however,the surge of construction land and the persisting declination of vegetation coverage can both lead to the increase of river runoff and sediment.The impact that change of vegetation fraction has on sediment and runoff is consistent in variation trend.The runoff-sediment-yield volume in every land type select from low to high is:woodland>grassland>arable land>bare land,but vegetation change has a more significant impact on sediment yield.If the organic unity of economic benefits,social benefits and ecological benefits is wanted to be achieved in Qinjiang river,it will be a good way to maintain the status quo and convert sloping field whose slope is less than or equal to 25°and which is not suitable for cultivation into forests responding to the call of government,on the basis of land-use planning,and return cultivated and construction land which is located on both sides of river and low-lying to forests or grassland.It is the same important to strengthen the management of water source region and forbid blind expansion of construction land,transform cultivation method and rationally allocate land-use resource in the river. |
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