Water Adaptability And Optimization Strategy Of Open Space In Dalian Core Urban Area

As a hotspot domain of urban stormwater management research,mechanism of the water adaptability and optimization of urban open space can provide reference for the construction of urban ecological civilization,which is of great value for improving the flood resilience of urban public space and promoting its hydrological and ecological functions.This paper takes the characteristics of hydrological structure of the core urban open space in Dalian as the research object.With the help of ArcGIS and eCognion9.0 analysis technology,the open space of the research area is identified on space and calculated on vegetation coverage ratio by using four types:parks,squares and sites,blocks,other shared spaces(street shared space,greenway,etc.),in combination with the DEM digital elevation in the study area to describe and analyze quantitatively its three-dimensional morphology and distributive property with the help of landscape layout index and spatial statistics.The parameters of vegetation interception and surface permeability can be obtained,based on the measurement of the soil of typical space underlying surfaces in different terrain gradient,then with the help of hydrological analysis model of Arc Hydrology to simulate the process of urban surface runoff in research area.With the help of supply and demand calculation of rainwater runoff regulation service,it can evaluate and analyze the water adaptability in open space,which reveals the water adaptability and main control factors of open space in the research area.Finally this paper puts forward corresponding optimization advice,which can provide ideas for the development and construction of low impact urban open space.The main results are as follows:(1)Parks and other shared spaces are the main landscape types of open space in the core urban area of Dalian.The overall connectivity and connexity of open space are high,but the patch uniformity is low and the distribution is unbalanced.With Olympic Square and People’s Square as a core area,the vegetation coverage ratio and spatial distribution of each type showed obvious aggregation characteristics,with a significant spatial positive correlation(P<0.01).Relying on the natural mountain and plant community,the open space and vegetation coverage ratio are high in the southwest and southeast,while the vegetation coverage ratio of the open space decreases gradually as it goes north.The terrain of open space changes greatly.The terrain of open space changes greatly,and parks and other shared spaces are mainly distributed on medium and steep slopes,while squares and blocks are mainly distributed on flat and gentle slopes.The highest landform bit index appears in the park,but other shared spaces had the most obvious distribution advantage in the low landform bit.The spatial structure,spatial type and attributes,topography and geomorphology are the important factors that affect the urban open spatial distribution pattern in research area.The uneven distribution of open space.the natural shortage of natural vegetation in the north and the richness of topography make it difficult to control the flow rate and velocity of rainwater runoff in the open space in the research area.(2)The bulk density of 75%open space is more than 1.3g/cm3 and the soil tends to be clay soil with less voids.Soil water content and water holding capacity in open space are generally low.which is bad for plant growth and hydrological regulation.The soil permeability rate of four open spaces are Parks>square and other kinds of sites>blocks>other shared spaces,and all of them show the rule of initial permeability>average permeability>stable permeability.The initial permeability,average permeability and stable permeability of parks and other shared spaces under different terrain indexes all show the law of low terrain level index,medium terrain index and high altitude shape index.The change law of initial permeability of parks and other shared spaces with different slope positions is the highest at the top of the slope,followed by the middle of the slope and the lowest at the bottom.In addition to topography,bulk density,water content and non-capillary porosity are also the main factors affecting soil infiltration in open space.Bulk density,water content and infiltration rate are negatively correlated,while non-capillary porosity and soil infiltration rate are positively correlated.(3)The spatial pattern of runoff regulation service in open space is similar under different rainfall intensity,and the changes concentrated in some smaller patches.The areas with the best service response were concentrated in the hilly areas with high density of vegetation cover in the southeast.In the west and north of the city,the density of open space decreases,the service response decreases,and the water adaptability decreases gradually.In the case of rainstorm,the service level of open space along the longitudinal corridors in the middle of the city is often reduced.The response of runoff regulation services in urban parks and other shared spaces is decreasing from east to west.The response levels of runoff regulation services in urban squares and various sites were lower in the north and higher in the south under the two rainfall scenarios.The service response level of the districts is high in the east and low in the central and western regions,the total service budget is generally low,and the adaptability of rainwater is poor.The overall water adaptability of open space is better in the east than in the west,better in the inland than in the coastal areas,and better in urban parks and other shared spaces than in squares and various blocks.The main factors influencing the water adaptability of Dalian open space are the open space distribution,topography,vegetation coverage and drainage facilities.From the general rainfall situation to the rainstorm situation,the threshold of vegetation coverage rate is increased from 42%to 58%to achieve the basic balance of runoff regulation supply and demand.With the increase of rainfall,the adverse drainage facilities around the space will also affect the performance of runoff regulation service and water adaptability in open space.(4)According to the above research results,the optimization suggestions and control strategies are put forward from three aspects:spatial distribution,soil infiltration characteristics and runoff regulation service.In terms of spatial distribution,it is suggested to improve landscape pattern,balance vegetation coverage and conform to terrain factors.Combined with the characteristics of soil infiltration habitat,it is suggested to construct two kinds of water-suitable vegetation community models:the dominant infiltration promoting type and the dominant retention type,then select the vegetation community model according to the infiltration zone of soil topographic potential index.According to the comprehensive evaluation of runoff regulation service,it is suggested that four kinds of spatial units should be classified and optimized.The water adaptability is better,and the red line of water ecological protection in mountain forest space should be strengthened.The area with moderate water adaptability should be strengthened to build a reasonable water resources ecological network.The weak water adaptability area should make up for the gap of service supply and strengthen the formation of water ecological compensation mechanism.In regions with large differences in water adaptability,the balance of spatial services and connectivity should be improved,while the construction of urban soil improvement,drainage network upgrading and low-impact development facilities should be strengthened.