Study On Soil Anti-scourability And Its Influence Factors Of Water-level-fluctuating Zone In Xiaowan Reservoir,the Lancang River

The hydrodynamic process of water-level fluctuating zone(WFLZ)is different from that of natural rivers,and it also changes the nature of the soil.With the low water level of reservoir,the exposed soil are lost by the rainfall runoff.In order to investigate the process of soil erosion caused by rainfall runoff in the water-level fluctuating zone,soil anti-scourability is used as an indicator.To obtain the variation of soil anti-scourability and its influencing factors is contrasting with soils of different types and dry/wet alternating processes,slopes gradient,slope lengths,and runoff discharge,by combing with field and indoor experiment.The results combined with the hydrodynamic factors is to obtained the influencing mechanism of the intrinsic regularity of soil anti-scourability,to provide important theoretical and practical base for estimating and monitoring the soil erosion status in the region and establishing the relevant physical model of soil erosion.The main conclusions of the study are as follows:(1)The change law of soil anti-scourability in the water-level fluctuating zone shows a decreasing relationship with the exponential function.At first,the sediment concentration came to peak,then gradually decreased,reaching the stable value with fluctuating.The soil change law of anti-scourability of grassland and bare land in the water-level fluctuating zone is both the same,but that of grassland is much better than of bare land,and the maximum difference is 68.71 times.The water-level fluctuating zone experienced an alternating wet and dry process,and its soil anti-scourability had an increasing trend compared with the non-water-level fluctuating zone(NWLFZ),but the difference between the two was not significant.(2)The topography(slope length and gradient)and runoff have a significant effect on the change of soil anti-scourability.The slope length and soil anti-scourability have an exponentially increasing relationship,while the slopes have an increasing logarithmic function.In Xiaowan Reservoir,the critical slope of water-level fluctuating zone is 20°~30°.The effect of runoff on the change of soil anti-scourability is as follows: at small flow rates,runoff is apt to be aggregated earlier due to terrain effects,and grooves and rills are formed on the slope surface,resulting in a higher sediment concentration;middle runoff discharge and large runoff discharge,the runoff flushes the slope surface in sheet flow,and is slightly affected by the terrain,resulting in a smaller sediment concentration and increasing with the increase of runoff discharge.(3)Among the hydraulic parameters,the Reynolds number,Froude number and drag coefficient can better reflect the changes of soil anti-impact,and the Froude number,runoff power and unit runoff power can predict the soil anti-scourability.The Reynolds number,Froude number,runoff shear force,drag coefficient,runoff power,and unit runoff power change with the flushing runoff discharge.Under the influence of the land type,they show different trends.From the viewpoint of energy consumption,the change law of soil anti-scourability was a good linear positive correlation in the grassland.