流域尺度土地利用调蓄视角的雨洪管理探析

发达国家雨洪管理焦点历经管网设计、不透水面阈值控制、低影响开发及土地利用管理等过程,呈现"多尺度多视角衔接"趋势。本文聚焦太湖流域土地利用调蓄功能变化机制及管理应用,揭示了1985-2015年来建设占用耕地是调蓄功能降低的主要原因;发现基于小流域的调蓄功能变化与建设用地强度整体低关联,但局部高相关,高相关的地区位于大城市或某些乡镇周边的建设增长热区,而这些热区的建设用地与调蓄空间规模较大且接触机会更多,是开发之前调蓄空间保护、开发控制以及开发之后综合管理等3个土地利用调蓄目标因子协调不当的结果;最后提出流域尺度土地利用调蓄视角的雨洪管理"345"模式,即以3个目标因子和5类控制要素为基础,实施土地利用调蓄创建、防御、拓展与保护等4类差别化战略模式,从更大尺度认识老城区和新区的雨洪关联,拓展海绵城市建设的本土认知和视野。

Modelling stormwater management based on infiltration capacity of land use in the watershed scale

The focus of urbanization effects on floods has gradually extended from the design of hydraulic channels to the control of imperviousness ratio and urban land use pattern in urban areas or the urbanized watershed. The stormwater management needs to integrate multiple floods perspectives in a spatial hierarchical unit, such as building, lot, city, watershed and region. However, the spread of the use of the urban landscape for managing and controlling stormwater in urbanized basins has been rather slow. The Low Impact Development (LID) model, which is used as the word of sponge city development in China, is used widely in Chinese cities. But most of Chinese cities, especially in East China have a high urban land intensity and no enough sponge city spaces to absorb surface runoff. The strong floods relationship exists among these spatial scales such as lot, city, watershed and region. Thus, the impact of land use change on environmental conditions improves the scientific knowledge on the floods correlation between new urban districts and downtowns, and expands the range of application of the LID/sponge city development. Then, the decline in the infiltration capacity resulted primarily from the transformation between construction land, cultivated land and other land use changes. However, there is low correlation between the infiltration capacity (CNc) and the construction land growth intensity in the overall sequence of development intensity (CLI15), but a high correlation in local parts of the CLI15 value. The high correlation occurs in the two parts of the CLI15 such as 8%-15% and 24%-39%, which are located in the "hot areas" of urban land growth around big cities and some rapidly developing towns. There is plenty of construction land and ecological infiltration space, and more opportunities to spatially contact together. Especially, three important target factors of the infiltration capacity in land use, such as the protection of infiltration spaces, land use control and LID-IMPs, are insufficient in the integrated planning and management. Last, the paper proposed a "3+4+5" stormwater management model in improving land use infiltration capacity, namely, three target factors, five key management elements and four management strategies models. Most parts of Area A in Taihu Lake watershed have a high intensity of land development, and implement the offensive strategy of improving the capacity of the hydraulic channels in the flood-prone areas, and create new ecological spatial elements in the right places. Area B around big cities is the main implementation area of the sponge city development/LID-IMPs, and controls the size of incremental construction land, and optimizes the pattern of construction land and natural spaces based spatial forms. Areas C and D are the main protection areas, and integrate stromwater management with land use zones, and expand and improve the ecological quality of natural service function.