Study On Runoff And Sediment Characteristics From Unpaved Road In Three Gorges Reservoir Area

Unpaved road in the mountains is a broad distribution of the type of road,which bulk density is high,saturated infiltration rate is generally low.Runoff can be formed in smaller rainfall intensity on the unpaved road because of the soil properties.So unpaved road is one of the main regional forming HOF in the watershed.Therefore,the unpaved road is a kind of the special erosion environment,which characteristics about hydrology and the erosion of law is different with the general slope and gully.The government has constructed a large number of roads in the course of migration and Protecting the ecological environment,in the Three Gorges Storehouse district.However,limited to poor economic conditions,the most part roads are not paved.In view of erosion and sediment issues is the most important to the Three Gorges Reservoir.In this project,the Wangjiaqiao Watershed,located in the Three Gorges Area,is used as a case study area to understand the impacts of unpaved roads on hydrologic processes,sediment transport, and sediment delivery at small watershed scale from a multidisciplinary perspective.In this project,the unpaved road is classified two kinds for their different road surface physical properties:village road and rural road.The artificial rainfall intensity is 0.5 and 1.0 mm/min for the control of man-made.The main results as follows:(1) The gravel concentration and soil capacity of unpaved roads are higher than the other slope.Most of soil capacity generally reach 2.0 g/cm~3 in rural roads.Saturated infiltration rate is very low,as low as 1.6 mm/h.Soil moisture content is generally lower. Vegetation cover in unpaved road is small.Under the disturbance from human being, there is a large of floating dust which loss easily by runoff.Such as it is 0.4 kg/m~2 in some rural road.(2) Runoff appears quickly.The cumulative rainfall before runoff is smaller.Such as runoff all appeared as the cumulative rainfall＜4 mm.when I=0.5 mm/min.When I=1.0 mm/min,the cumulative rainfall＜2 mm.The runoff coefficient is all larger than 70 percent.The runoff coefficient on unpaved road is generally larger.The runoff coefficient increases very quickly in the initial stage of the tests.And then it gradually becomes steady in continued rainfall processes.In contrast to rainfall intensity,the type of unpaved road impacts weaker runoff.However,When I=0.5 mm/min,There is a significant interaction between gravel concentration and runoff coefficient.(3) The sediment concentration is very high in the initial stage of soil erosion processes by runoff on road.However,the concentration decreases very quickly,and then gradually becomes relative steady in continued rainfall processes.The Max sediment concentration is 28.58 g/L on rural road in 1.0 mm/min.When the rainfall accumulated 9 mrn,the sediment concentration of rural roads dropped 52.2%,and the village roads have reached 34.6%.The most sediment on unpaved road is from floating dust.With the cumulative rainfall increased,floating dust depletion,unpaved road erosion by runoff as a major source of sediment.(4) The erosion rate impacted by runoff and the scource of sediment.The variation of erosion rate with rainfall process is great in the initial stage of soil erosion processes by runoff on road,then it is relatively steady..There is a significant interaction between erosion rate(F=6.082~*),sediment concentration(F=1.296~*)and the types of unpaved road.The relativity of soil bulk density,floating dust and erosion rates is significant.The relativity of Vegetation,gravel concentration and erosion rates is high,.but not significant.