Study On Sediment Transport In Urban Small Watershed

Global climate change,depletion of resources and deterioration of the ecological environment have caused mankind to fall into the ecological dilemma of its own directors.A series of problems such as environmental pollution,forest destruction,serious soil erosion and desertification pose a serious threat to human survival and sustainable development.Countries in the world,while developing industrial and agricultural production and carrying out basic construction,are constantly destroying natural vegetation,causing land degradation and increasing soil erosion.Soil erosion not only destroys land resources and causes a decline in land productivity,but also is the main influencing factor of disasters such as ditch and dike storage,mountain collapse and debris flow,which directly restricts the sustainable development of agriculture and the protection of ecological environment.Therefore,in order to prevent soil erosion,it is particularly important to study the law of sediment transport process.The influence of the climate,topography and human activities of the watershed has always been the main factor affecting the runoff and sediment production of the watershed,and it is also an important field of soil erosion research in small watersheds.Human activities have exacerbated changes in the underlying surface of the watershed,which has affected the erosion and sediment transport and deposition of the watershed system,resulting in major changes in the characteristics and processes of water and sediment in the watershed and river.Calculating sediment deposition and sediment transport is an important scientific basis for rational use and management of land resources,and different rainfall conditions and watershed land use types are the main factors affecting the generation and carrying capacity of surface runoff.Therefore,there is an intrinsic rule between the distribution of surface water particle size and rainfall and land type in the watershed.Although much research has been conducted on the relationship between rainfall and soil erosion in the watershed,it appears that the existing studies have mainly focused on changes in erosion(such as differences in total soil erosion at different slopes or different land types).In this study,we observed the changes of runoff,eroded sediment and the particle size distribution of sediment particles in the urban small watershed from multiple scales.Reveal the flux and distribution of surface runoff sediment transport process in small watershed.This subject uses the HEC-RAS software to establish a hydraulic model and a sediment model for sediment transport analysis and calculation.Through the research and calculation of the model,the regular changes of the sediment transport process are obtained.The study of sediment transport law has important practical guiding significance.The research results of the thesis are as follows:(1)The paper calibrated the linear relationship between turbidity and sediment concentration in the Wutong Mountain watershed.The greater the rainfall,the faster the drainage basin and the greater the flow.At this time,the current has strong sand-carrying capacity,the turbidity of the current is large,and the sand content is also high.At the same time,the amount of sediment migration is large,and the increase in the total amount of sediment is also greater,causing more serious siltation at the river bottom.(2)As the sediment will migrate from the upstream to the downstream of the river channel with the flow of water,there is less sediment in the upper reaches of the river channel,and the amount of siltation at the river bottom is also small;sediments in the middle reaches of the river channel gradually increase,and the amount of siltation at the river bottom will also increase;The downstream sediments are the most,and the siltation at the bottom of the river also reaches the maximum.In September 2019 and two heavy rains,the siltation depth and volume of each section showed an upward trend from upstream to downstream.(3)The siltation depth and siltation volume will be reduced to a certain extent at the exit.In September 2019 and two heavy rains,the siltation depth and siltation volume are very large at the 220 section and 200 section of the station,but at the exit The section of stake 80 has been reduced.(4)Because the topography of the bend of the river channel has changed,the sediment will increase significantly when the water flows through,and the amount of river bottom siltation will also increase significantly,so the siltation sites are mainly concentrated in the place where the river topography changes.In September 2019 and under two heavy rains,the pile number 3700 section at the upstream curve,the pile number 2000 section at the midstream curve,and the pile number 1000 section at the downstream curve,compared with the nearby sections,the siltation depth and the amount of siltation are all Larger.(5)As the rainfall of the 20190828 heavy rains was much greater than the 20190801 heavy rains,the runoff was also greater,the sediment-carrying capacity of the water flow was stronger,and the sediment deposition speed and start-up speed were faster.Therefore,the siltation depth and volume of each section of the 20190828 heavy rains are much greater than the 20190801 heavy rains.Comparing the growth rate of the total amount of siltation in the two heavy rains,it is found that the increase rate of the siltation amount also increases with the increase of the flow.(6)Runoff and sediment production caused by rainfall is the main contributor to the total amount of runoff and sediment yield in small urban watersheds.Small urban watersheds produce less runoff and sediment,and the amount of sediment migration with water flow is also very small.Therefore,the amount of river bottom siltation is also very small,and there will be no serious siltation,so there will be no impact on the riverbed,river diversion,etc.Will cause too much impact downstream.