Landscape Planning And Design Of Small Watershed In Mountainous Hilly Region Based On Stormwater Management

Mountain flood disaster refers to the complex natural disaster caused by short-term heavy rainfall events such as mountain flood and its chain reaction(such as debris flow,landslide,rockfall,etc.),which has sudden and great destructive power,and has become one of the most major catastrophe in the world.The eastern part of Henan Province is mostly mountainous and hilly area.Mountain torts of different sizes occur every summer,which bring heavy pain to local people and seriously restrict the economic and social development of mountainous areas.It has become one of the most prominent disaster problems in Henan Province.Therefore,it is very important to study the temporal and spatial distribution of mountain flood evolution,explore its influence mechanism,accurately assess disaster risk and formulate land regulation and control plan in risk areas for guiding disaster prevention and mitigation and improving mountain flood risk avoidance.The "Heavy rain on July 20,2021" flood event in Zhengzhou City,Henan Province provided a unique opportunity to study the flood disaster in small watersheds in mountainous and hilly areas.This historic flood event resulted in a large number of casualties and property losses.Based on the Gaofen-6 remote sensing data,ALOS-PALSAR surface elevation data and hourly rainfall data,this study constructed a two-dimensional hydrological model of the Jiayu River Basin by using the MIKE 21 hydrodynamic model,and analyzed the flood distribution law of the upper,middle and lower reaches during 0-24 period of July 20,2021.Based on analytic Hierarchy Process(AHP)and waterlogging risk function expression,the mountain flood disaster risk assessment model was constructed,and the mountain flood disaster risk zoning map and flood disaster risk grade map were drawn in the Jiayu River basin.Combined with the bivariate spatial autocorrelation model and the geographic detector model,the differences of temporal and spatial correlation between flood intensity and landscape composition and topographic factors as well as their spatial clustering types were explored.Finally,based on the research results,optimization strategies to enhance the rain-flood resilience of the Jiayu River Basin are proposed based on different spatial landscape characteristics.The main conclusions are as follows:(1)The submerged area of the Jiayu River basin increased rapidly from 0 to 6,gently from 6 to 18,and reached the maximum 9.59km2 at 18.At this time,the proportion of submerged area of each region was 18.88% in the downstream,8.25% in the upstream and 12.03% in the middle,and the area with the submerged depth of more than 3m accounted for 36.11%.(2)The spatial distribution of "7·20" flood risk level in the Jiayu River basin showed a downward trend along the river course.The area of the extremely high risk zone accounted for 3.43%,mainly concentrated in the central north,and scattered distribution in some parts of the south.The overall spatial distribution characteristics of mountain flood risk showed a trend of low in southwest China and high in northeast China.The area with high risk accounts for about 1.81%,which is mainly located in the open pit in the upper reaches of the south,the middle reaches,the surrounding areas of the southern river in the lower reaches and the West Fourth Ring Road.(3)Topographic factors(mean Moran’s I=0.159)had a greater impact on flood intensity than land type(mean Moran’s I=0.096).The correlations between the relative elevation,topographic humidity index,green infrastructure area percentage and flood inundation intensity increased over time.All of them were strongest at 18~24 hours in the middle and late rainstorm.The cross-detection results show that the superposition of multiple factors can enhance the influence of landscape features on flood inundation intensity.In the upper reaches,the main driving forces affecting flood inundation intensity are mine pit and relative elevation,while in the middle and lower reaches,the main factors affecting flood intensity are water body and terrain moisture index.(4)According to the above research and analysis results,landscape planning and design of Jiayu River Watershed based on stormwater management measures were carried out.The landscape planning scheme is planned and designed from three levels: macro overall planning layout,mesoscopic zoning planning and micro special restoration.At the macro level,the spatial security pattern of "one axis,three zones and multiple nodes" is constructed from the natural conditions and flood risk zones of the watershed.From the perspective of habitat restoration and sustainable development,the planning concept of the middle zone is to create the upstream ecological restoration area,the middle ecological management area and the downstream ecological protection area.The site optimization design is mainly carried out from the aspects of landscape restoration of open pit,ecological design of riverbank zone,habitat construction of water source and urban landscape grid planning,so as to enhance the rain-flood resilience and landscape ornamental value of the watershed,so as to improve the overall habitat quality of the watershed.This paper takes the small watershed of Jiayu River in the mountainous and hilly area in the southwest of Zhengzhou City,Henan Province as an example to guide the design practice with the results of theoretical research.From the perspective of the response of watershed landscape characteristics to the inundation intensity of rain flood,the ecological space restoration planning and design strategy was proposed to help the protection and restoration of wetlands in the Jiayu River basin,and to provide certain ideas and reference experience for landscape planning and design of related mountainous and hilly areas in Henan Province.