汾河流域超长尺度低频洪水水文重构与淹没效应评估

The lack of cognition of low-frequency flood characteristics limits the precision of engineering design flood and watershed flood risk assessment. Field investigation and samples collection will be taken in the Fenhe River basin at the beginning of this project. Through experimental test and physicochemical analysis, combining with particle decomposition model, the typical low-frequency flood deposits will be discriminanted. The particle state, flow state and sedimentary mechanism of the low-frequency flood process will be analyzed with the deposits’ microscopic features and sedimentary dynamic pattern. The chronostratigraphic framework of low-frequency floods deposits will be established by using the optically stimulated luminescence and stratigraphic contrast method. According to the flow field characteristics and hydrologic regime of sedimentary environment, the cross-section shapes and depths of low-frequency floods will be restored. The high-resolution eigenvalue and long-term sequence of low-frequency floods will be reconstructed by the hydrological and hydrodynamic coupling model. Based on the process and the law of geomorphology evolution, the low-frequency flood level and inundation area model will be constructed. And the inundation situation of modern low-frequency floods will be simulated under different frequency scenarios. Thus, it is not only significant to provide a basic reference to flood forecast, emergency plan formulation and water resources regulation in Fenhe River basin, but also important for engineering construction and mitigating flood disasters in the middle and lower reaches of the Yellow River.

低频洪水特征认知的缺失限制了工程设计洪水和流域洪水风险评估精度。本项目拟基于汾河流域深入细致野外考察和样品采集，通过实验测试与理化分析，结合粒度端元分解模型分析样品颗粒组分，判别典型低频洪水特征沉积物质特性；借助沉积物微观特征和沉积动力格局，探究低频洪水过程颗粒状态、流态和沉积作用机制；综合光释光测年技术和地层年代对比法，建立可靠的研究区域低频洪水沉积年代框架；依据沉积环境流场特性与水文情势，复原行洪断面形态，明晰低频洪水沉积层厚度-颗粒浓度-水深响应关系；运用水文-水动力耦合模型，定量高分辨率低频洪水事件特征值，重构超长尺度低频洪水序列；根据研究区域河流地貌演变过程和规律，构建低频洪水水位-淹没面积模型，模拟不同频率情景下研究河段现代低频洪水淹没情况。研究可为汾河流域洪水预测预报、应急预案制定和洪水资源化提供新的科学依据，对于黄河中下游大型水利水电工程设计和洪水管理都具有重要的现实意义。

项目针对汾河流域水文序列较短和低频洪水特征认知缺失的问题，开展了低频洪水的超长尺度水文学重建与不同频率情景洪水的模拟。.基于对汾河流域深入细致野外考察和样品采集，利用沉积学与地球化学代用指标，揭示典型低频洪水特征沉积物分选性好，粒度组分以粉沙为主，属于高水位滞流悬移质沉积物；综合光释光测年技术和地层年代对比法，确定研究河段低频洪水沉积事件发生年代为4200-3900aBP，对应着下游陶寺文化从繁盛走向消亡；依据低频洪水沉积层厚度-颗粒浓度-水深响应关系，定量高分辨率重建低频洪水洪峰流量介于13480-13590 m3/s之间；运用SAM和HEC-RAS模型，模拟“万年一遇”“千年一遇”“百年一遇”不同频率情景下研究河段低频洪水流量和淹没情况。超长时间尺度洪水序列不仅有效延长了汾河流域水文序列，而且为流域洪水预测、风险评估和资源化提供新的科学依据，为流域内龙山文化晚期古文明的消亡提出了新证据。