Study On Flood Response To Urban Expansion In Lushui Basin

With the acceleration of China’s economic construction and the level of urbanization continues to increase,water problems have become increasingly prominent.The Xiangjiang River is one of the seven major tributaries of the Yangtze River.Lushui is a first-level tributary of the Xiangjiang River.The Lushui watershed is located in hilly areas and the rainstorm areas in eastern Hunan.In addition,the cities in the watershed have expanded rapidly.In recent years,many catastrophic urban floods have occurred.This paper focuses on the flood response of the tributary of the Xiangjiang River in the context of urban expansion,and provides a reference for future urban flood control and disaster reduction.The main research contents and conclusions are as follows:(1)This paper extracts the changes in the underlying surface of the basin based on the remote sensing images from 1980 to 2018,and analyzes the spatial expansion of the city,studies the law of urban expansion,builds an urban expansion model,and completes model calibration and verification.The results show that the area of construction land in the Lushui Basin continue to grow from 1980 to 2018,and the growth rate accelerated gradually after 1995 until it reached its peak in 2005.Slopes,water systems,transportation,population,and administrative centers all have certain effects on urban expansion.Summarize various driving factors and impact weights to construct a CA Marrkov model for river basin urban expansion and evaluate the simulation accuracy(2)Based on the hydrometeorological data from 1965—2017,this paper compares and analyzes the changes in flood elements and changes in the rainfall-runoff characteristics,and also studies the impact of urban expension on flood in different periods by constructing similar rainfall groups.The results show that both the characteristic values of storm and flood show an upward trend.Selecting multiple sets of similar rainfall scenarios before and after the rapid expansion of the river basin city and studying the corresponding flood process differences,it is analyzed that after 1995,the runoff depth of the floods and the flood peak is increased.And the time when the flood peak appeared was generally early(3)The author constructs HSPF flood models and completes model calibration and verification.Based on the constructed hydrological model,the historical inversion method was used to analyze the response of historical floods of different magnitudes to the underlying surface changes.By comparison,post 1995,the Lushui Basin’s runoff efficiency is higher than that before 1995.Flood peak flow and runoff depth have both increased.The impact of changes in the underlying surface conditions on the floods is also related to the magnitude of the flood.The greater the flood magnitude,the lower the degree of impact caused by the changes in the underlying surface conditions.(4)With the help of the constructed urban expansion model,four development models are designed to simulate the urban expansion scenarios of the river basin in 2050.Based on the flood model,this paper studies the response of the future underlying surface to historical floods under different development models.The results show that optimizing the land use pattern and accelerating the concentration of rural population in larger cities can improve the efficiency of rural land use,and facilitate the implementation of the cultivated land protection system,and at the same time weak the flood process.On the basis of cultivated land retention,permanent basic farmland protection area,and high-standard farmland construction,the implementation of returning farmland to forest will further weaken the flood.Conducive to urban flood prevention and sustainable development.