海河山区迎风坡包气带变化影响下洪水形成机制与模拟方法

As the flood source area, the windward slope of mountainous and hilly area of Haihe River Basin has a large annual rainfall and strong soil infiltration ability, therefore, the infiltration-excess surface runoff is not easy to occur. However, due to the decrease of the groundwater level and the thickening of the vadose zone, the stored-full runoff generation pattern is also not easy to appear. At present, the threshold of runoff generation in Haihe river basin increases sharply, and heavy rainfall generally does not produce runoff and rivers dry up. However, the extreme rainstorms in 2012 and 2016 caused severe flood disasters. How to simulate the flood formation process in mountainous and hilly areas under the condition of semi-humid climate and thick vadose zone has become a major problem in flood control and disaster reduction of Haihe River Basin. In this study, the temporal and spatial variation of the runoff threshold and the corresponding dominant factors will be revealed by statistical analysis of the hydrological data，underlying surface data and vadose zone data, the threshold mechanism of runoff generation on the dry river bed will be investigated by soil moisture monitoring in the river bed sections, the threshold mechanism of runoff generation in the hillslope under the condition of thick vadose zone will be investigated by the physically-based distributed modeling, and finally, combined with simulation of actual and virtual runoff conditions, the rainfall-runoff and storage-outflow constitutive relationships reflecting the characteristics of high threshold runoff will be constructed. The research results can reveal the influence mechanism of vadose zone thickening on the runoff generation in semi-humid areas, and can also put forward the rainstorm flood simulation method which reflects the characteristics of high threshold runoff and improves the accuracy of flood forecasting. In this sense the research has great scientific and application values.

海河山区迎风坡作为洪水源区，年雨量大，土壤下渗能力强，超渗地面径流不易发生；然而由于地下水位下降、包气带增厚，蓄满产流模式也不易出现。当前海河流域产流阈值急剧增大，暴雨等级降雨都难以产生径流、河道干涸，而2012、2016年特大暴雨则造成严重洪水灾害。半湿润气候条件厚型包气带环境下，山丘区洪水究竟如何产生与模拟，成为海河流域防洪减灾的重大问题。本项目拟通过对水文资料及下垫面、包气带资料的统计挖掘，探究产流阈值时空变化规律及主导因素；基于河道断面土壤水分监测分析，研究干涸河道径流形成阈值机制；利用分布式物理水文模拟，研究包气带增厚影响下坡面产流阈值机制；最后，结合实测模拟与虚拟仿真，构建反映流域高阈值产流特性的降雨-径流、蓄量-出流本构关系。研究成果能够揭示包气带增厚对半湿润流域径流形成的影响机制，也能够提出反映产流阈值变化特点的暴雨洪水模拟方法，提高洪水预报精度，具有科学意义和应用价值。

由于地下水超采、包气带增厚，海河相当多流域出现了独特的高阈值产流现象：暴雨等级降雨都难以超过产流阈值，河道没有或只有微弱径流；特大暴雨则产生迅猛上涨的河道流量，造成严重洪水灾害。半湿润气候条件厚型包气带环境下，山丘区洪水究竟如何产生与模拟，成为海河流域防洪减灾的重大问题。本项目通过流域查勘、野外实验、统计分析、模拟论证等多种方式，取得如下成果：（1）分析了海河不同典型流域地下水逐渐下降、包气带逐渐增厚背景下大中洪水产流阈值和洪水过程的变化特征，发现了海河典型流域大中洪水产流能力呈趋势性变化、周期性变化以及非显著变化3种方式，主导因素是气候变化与人类活动影响相互叠加，气候周期性波动导致产流能力周期性变化，人类活动如地下水超采、包气带增厚导致产流能力趋势性变化；（2）发现了半湿润条件厚型包气带超渗产流机制不可忽视，总产流量大小取决于坡地汇流渗漏与河道汇流渗漏情况，初步发现了渗漏能力取决于粘土层的深度与空间分布；（3）通过野外同位素示踪与下渗实验，研究了包气带增厚影响下流域降水、河道水与地下水的转化关系，确定了包气带增厚影响下地表入渗的基本过程与基本参数，发现地下水超采、包气带增厚会增加产流阈值、增加产流损失，但增加的程度依赖于流域下垫面具体特征；（4）通过基于物理基础的分布式水文模型，发现地下水超采、包气带增厚背景下超渗产流也是半湿润流域径流形成不可忽视的重要机制；（5）基于前期概念性模型精度对比研究，改进新安江模型抛物线型蓄水容量曲线，在维持精度的前提下，加入产流阈值结构和参数，构建了考虑产流阈值的降雨径流本构关系；（6）检验栅格型新安江模型在秦淮河流域等天然湿润半湿润流域的合理性，之后移用于海河地下水超采、包气带增厚的半湿润流域并加以改进，构建了适用于半湿润流域厚型包气带的分布式水文模型。