| The interactive coupling relationship between urban landscape layout and stormwater resources distribution has become one of the hot topics in the study of landscape architecture and landscape ecology.There were differences from temporal and spatial evolution patterns and evolution paths between stormwater resources distributed unevenly,extreme events and urban landscape layout.In the process of urbanization,urban surface landscape characteristics change,river structure degradation,impervious surface area increase and other engineering trauma have completely changed the natural hydrological process of the city,which is an important reason for the coexistence of urban stormwater resource shortage.Scholars in developed countries have accumulated a lot of experience in the study and practice of rainwater resources allocation,which provides a foundation for related research in China.However,there are differences among countries in social background,geographical environment and other aspects in the historical stage of development.It is necessary to conduct an in-depth discussion on the characteristics of stormwater resources distribution in China.Luohe is located in the key area where the three tributaries Sha river,Li river and Ying river of Huai river,converge,where the downriver from the storm center in Henan province.The frequent occurrence of flood disaster,there is typical of the river network cities in the northern plain of China.In this study,the evolution characteristics of urban river landscape structure in the urbanization process of Luohe area,the spatial distribution characteristics of surface runoff in Luohe central district and the landscape pattern characteristics of flooding circles and dry circles in urban blocks were taken as the research objects.According to the data accuracy requirements of different scale studies,qualitative,quantitative and positioning analysis of the impact of urban landscape features on the distribution process of stormwater resources.The results are expressed in pictorial language,and put forward corresponding strategies and suggestions.The results are summarized as follows:(1)From 1999 to 2016,the percentage of total annual water resources in the same year's rainfall in Luohe was negatively correlated with the change of built-up area(sig.-0.537 *,P=0.021).This shows that the expansion of construction land in luohe is one of the reasons affecting the decline of total water resources in this area.In 2010,2013,2015 and 2017,interpolation analysis was carried out at 20 rainfall stations,and the rainfall centers were distributed along major rivers such as Li river,Ying river,Wugong channel and Hongru river.Among the 7 local soil types,the Yellow-cinnamon soils with good permeability are distributed along the Li river and Ying river.The annual average surface evaporation over the years is 807.5mm,and the annual distribution of the surface evaporation is uneven.The summer evaporation is large while the winter evaporation is small.The annual average summer evaporation(5 to 8)accounts for 51.2% of the annual average evaporation over the years.There are 81 rivers in Luohe,with abundant transit rivers but insufficient lakes and wetlands.Over pumping of groundwater has led to local water shortages.(2)In the landscape of Luohe from 1988 to 2017,the grid of rivers density presented an aggregation feature,but the spatial clustering distance increased significantly and the aggregation gradually decreased,transforming from high density to low density.The interaction of rivers has weakened and the spatial dependence reduced.The structure of river network transformed from multi-cores distribution to single.The water area decreased and the conversion rate was 23.60%.The main influencing factor was the increase of urban construction land area.The number and length of rivers have declined overall,the higher the river grade,the fewer and shorter the river.Lower grade of rivers decreased and high grade of rivers transformed to Lowe grade of rivers.The rainfall and flood resources tend to be concentrated and distributed.(3)The continuous growth of construction land in urban central district of Luohe showed an aggregation feature,with a tight central structure and a multi-core distribution in the periphery,and the decrease of spatial aggregation showed a centrifugal development trend.Land cover/use(LUCC)presented a progressive feature,from the urban center to the edge,the proportion of construction land was gradually reduced,and the permeable landscape was gradually transformed from urban green land into farmland.Moran's I coefficient of total runoff,runoff coefficient,runoff volume and peak flow in urban central district,shows that TR and RC are 0.338(p<0.001),RV is 0.142(p<0.001),TP is 0.101(p<0.001).They spatial distribution and the change of construction land show significant agglomeration.The spatial distribution of TR and RC is consistent,decreasing from the city center to the edge,and the spatial distribution of RV and TP was consistent,which was greatly affected by the catchment area and the distribution of urban pipe network.Through the analysis of minimum cost distance,the potential number of 491,820 has connectivity and directivity,which could directly show the distribution path of runoff.According to the selection by gravity model,the gravity intensity 18.93 was the maximum threshold for the connection of the whole catchment areas.As the gravity intensity increases,the potential runoff path in the catchment area gradually disconnects,showing the important areas and sequence of runoff distribution.The potential surface diameter density was highly significantly positively correlated with the spatial distribution of runoff generation process(r=0.602**,p=0.000<0.01),showing significant aggregation and decreasing from the center to the edge.(4)The infiltration capacity of the permeable surface landscape of Luohe city block decreased with the increase of rainfall intensity,and the Hortonian overland flow threshold was 21 mm/h.The landscape index of buildings and roads in the impervious surface landscape were at a high level and consistent,which was the leading landscape factor causing local flood in Luohe city.There were significant differences in landscape area ratio and landscape shape index between buildings and roads in flood circle(FC)and dry circle(DC),which were the keys index to determine whether buildings and roads cause local flood.LSI,MPS and CONNECT of permeable landscape patch of urban stormwater management to a certain extent,but not the dominant element.Penetration landscape PLAND and MPS have significant role to alleviate stormwater,while the LSI and the CONNECT was not significant.But CONNECT of green space between DC and FC were significant differences,explain that good connectivity of urban green space has positive effect to relieve flood.(5)This study proposed the optimization strategy of water-ecological sensitive area in Luohe urban watershed.Through the superposition analysis of topography,natural environment and construction factors,different ecological sensitive areas were determined and control guidelines were proposed.For the management of stormwater resources in Luohe central district,the priority management level of surface runoff and the optimization strategy of network construction are proposed.According to the level of runoff production,flooding and runoff density distribution,the integrated level and the priority management area are developed.The protection focus and the key position are defined according to the distribution path of runoff.urban block LID reconstruction,supported by priority management area and runoff distribution path,can be targeted to control key points and implement precise reconstruction. |
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