平原河网地区水系结构演变对洪涝调蓄能力的影响研究

The study focuses on impacts of the stream system changes on storage-discharge capacity for the increasing flood disasters caused by the deteriorating of river-lake system under the background of urbanization and diking in plain network area, and the case study was conducted in Lixiahe district by analyzing the relationship of “River structure- connectivity- storage capacity”. Firstly, variation of structure characteristics index was selected and summarized to better analysize the spatial and temporal change of stream structure under intense human activities. Secondly, from the aspects of the construction, hydraulic characteristics and social importance et al., the river network connectivity was evaluated based on the hydraulic resistance and network path analysis, the method provided a feasible and effective way to establish the relatioship of river connectivity and structure indices to meet flood discharge capacity, then the storing capacity of region was investigated and its impact on hydrology process was discussed; Thirdly, the effect of river network storage capacity on flood was qualitatived by coupled hydrological and hydrodynamic model in different scenarios. Based on the above analysis, the relationship “human activities-stream structure-connectivity-storing capacity-flood” was established. This research may rich theoretical research on sream structure in plain area, and seeks the schemes and measures to improve the regional storage capacity and alleviate the flood risk by improve the river structure.

针对平原区围垦和城镇化背景下河湖水面减少、水系连通受阻等下垫面变化引起的洪涝加剧问题，拟以典型洪涝平原苏北里下河地区为例，以“水系结构-连通-调蓄”为主线，探讨水系结构演变对洪涝调蓄能力的影响。首先基于区域水系格局特征分析，从水系空间分布和数量特性等方面构建量化指标体系，揭示水系结构特征演变规律；然后综合考虑水系结构、水力特性和社会重要性等因素，提出满足行洪排涝需求的平原水系连通度量方法，揭示水系结构与连通度之间的物理和数学关系，分析水系结构和连通变化对区域调蓄能力的影响，以及调蓄能力变化下的降雨~水位关系变化特征；最后结合水动力学模型和暴雨情景分析，通过动态模拟不同水系结构和连通条件下的洪涝程度和时空分布特征，建立水系结构与洪涝调蓄能力之间的关系模型，在此基础上针对里下河地区防洪排涝需求，提出水系结构和连通性改善途径。研究成果将丰富平原水系结构理论研究，有望为区域水系规划提供决策支持。

流域下垫面变化对水文过程的影响研究是当前水文科学的热点问题之一，平原河网区通常是人类活动较为强烈的地带，河流众多，结构复杂，水系变化及水文影响研究尤为重要。本项目针对围垦和城镇化等影响下河湖水面减少、水系连通受阻等引起的洪涝加剧问题，开展平原区河流水系等下垫面变化对洪涝调蓄的影响研究。通过里下河平原与鄞东南平原等典型河网区的实证对比分析，建立了包含河网密度、水面率、连接度和盒维数等反映水系数量和结构的评价指标体系，梳理得出城镇化等人类活动影响下平原水系数量减少和结构单一化的趋势规律，以及水系变化与城镇化的关系特征；利用水力学曼宁公式和网络分析技术，综合考虑水系面积、空间结构和水力特性等因子，从行洪排涝角度出发，建立了河网连通性评价方法，为平原水系变化对连通性影响分析提供了技术和途径，并对河网连通度与骨干河道面积比指数和水系空间连接结构的响应关系进行了分析；另外从降雨~水位关系、水位站点间水位变化的一致性等角度，揭示了里下河等典型平原区特征水位增加、水文空间变异增强的一般规律，并利用弹性分析等方法评估了人类活动对河网水位的影响；最后，通过河网调蓄能力分析和洪涝情景模拟等技术，分析得出区域调蓄能力的减弱使得在相同暴雨情景下，洪涝水位增加，高风险范围扩大的趋势，以及河网调蓄能力受前期水位影响且受暴雨强度影响的特性。本项目研究可为区域水系规划、防洪减灾和环境保护提供借鉴。