Impacts Of Human Activities On Riverbed Evolution Of Jiaojiang Estuary In Recent50Years

Jiaojiang Estuary is located in the middle of the coast of Zhejiang Province, and it’s a hilly, fluvial and macro-tidal estuary. Runoff and trends are two major driving factors that control the evolution of this kind of estuary. With the development of socio-economic, the number of human activities in the estuary is increasing, and they Have some influence on evolution of the river bed.This article took the Jiaojiang estuary as an example to explore human activities’ influence on the evolution of the River bed in recent50years. And it would provide reference for future human activities. The study region is the Jiaojiang Estuary which is the lower reach of Lingjiang river, focusing on the reach from Shixianfu to Niutoujing. In recent decades, Jiaojiang estuary and it’s upper reaches are transformed by human activities, such as the construction of changtan reservoir in1962, the channel regulation projection of Jiaojiang estuary started in1987, the comprehensive management engineering of both Yongning river and Jiaojiang river started in1994. Besides these human engineering activities, human also excavated sand in the upper reaches of the Jiaojaing River.After the Changtan reservoir, The flow of Yongning river reduced and Yongning river appeared deposition, and the Jiaojiang Estuary appeared deposition. The government Implemented a series of projects to solve this problem, including the channel regulation projection of Jiaojiang Estuary started in1987, the comprehensive management engineering of both Yongning river and Jiaojiang river started in1994. Besides the human projects, the scale of sand mining in jiaojiang river was gradually expanding after the1980s, with the development of the city.Through the material and the results of other researchers, this article analyzed the influence of human activities.This paper analyzed the engineering measures’ impacts on Jiaojiang Estuary at first, After the Construction, The flow of Yongning river reduced and Yongning river appeared deposition, and then the Jiaojiang Estuary appeared deposition. So the channel regulation projection of Jiaojiang Estuary,the comprehensive management engineering of both Yongning river and Jiaojiang river were started. after these projects, the flow velocity and the ratio of tidal volume in south channel increased, and the south channel scours steadily, but the north channel is changeable. The change of the estuary channel will achieve new equilibrium. Then the paper analyzed the effects of sand mining activity on Jiaojiang Estuary, it Strengthen the estuarine tidal current power.In this article, the data of water depth and topography in Jiaojiang Estuary were processed with the surfer, ArcGIS software, from the results of the data, it thought that after the implementation of projects, erosion rates of Jiaojiang Estuary had gone through this process of slow-speed-slow. In addition, this article analyzed the mechanism of scouring and silting of the river bed of Jiaojiang Estuary, the human activities changed the Jiaojiang Estuary bed boundary conditions, caused changes in the dynamic conditions and sediment transport process. The Riverbed also made a corresponding adjustment. Human projects were not independent of each other without contact, at the beginning of Changtan reservoir construction, Because the project had not kept pace with others, resulting in later series of question, causing the other subsequent regulation. Therefore, before the commencement of works in the future, we must consider all the possible effects, advance planning, minimize its negative effects and maximize the positive benefits.