黄河流域水保措施对产汇流的滞蓄-间歇阻断作用机制及分布式模型构建

In recent years, the soil and water conservation measures (SWCM) have made the underlying surface of the Loess Plateau in the middle reaches of the Yellow River significantly become green, and the river flow and sediment sharply reduced. The phenomenon of "Clear Yellow River" quietly appeared. However, the fact that SWCM would be an amplifier of sediment load and flood when its storage capacity being exceeded also exists. In general, runoff generation in this region is dominated by infiltration excess (Horton) mechanism. However, the detention-storage effect caused by SWCM leads to the spatial-temporal heterogeneous transformation between infiltration excess and saturation excess (Dunne) runoff mechanisms. Meanwhile, the check dam system has the complex intermittent blocking effect on flow confluence process. It means that the underlying runoff generation and confluence mechanisms behind these phenomena have been changed. Currently, however, there is a lack of complete scientific understanding of these problems. This project taking the arid and semi-arid basins in the middle reaches of Yellow River as the study area, presents the analytic method of spatial and temporal evolution characteristics of the SWCM storage capacity through the combination of field survey and remote sensing interpretation. It designs the comparative observation of small experiment watersheds under different SWCM conditions, and further analyzes the detention-storage mechanism of runoff generation and quantifies the threshold. The infiltration mechanism of complex underlying surface condition would be studied based on the laboratory and field infiltration and hydrological experiments. The universal runoff generation scheme and the intermittent blocking flow confluence method based on the “grid drop” concept for dam system could be proposed in this study. Finally, the distributed hydrological model for SWCM integrated management regions would be developed.

近年来水保措施使得黄河中游黄土高原下垫面明显“变绿”、河道水沙锐减，悄然出现“黄河清”态势，但同时存在超过水保拦蓄能力后增沙增洪的事实。过去一般认为该地区产流以超渗为主，但水保措施诱发的产流滞蓄作用，导致蓄满-超渗机制的时空非均一性动态转换；而沟道坝系存在对汇流过程复杂的“间歇阻断”作用。这些现象背后隐含着该地区的产汇流机理已发生改变，但目前对这些问题尚缺乏完整科学认识。本项目以黄河中游干旱半干旱流域为研究区，基于“野外调查与遥感解译”结合的途径，提出水保措施拦蓄能力时空演变特征的分形解析方法；设计不同水保措施治理条件下的野外小流域对比观测实验，揭示水保措施对产流的滞蓄作用机制，量化降雨产流阈值效应；基于室内、野外小流域下渗与产汇流实验，研究复杂下垫面条件的下渗机理，建立普适的“统一”产流模式及耦合淤地坝“间歇阻断”作用的“网格水滴”汇流方法，构建考虑水保综合措施影响的分布式水文模型。

随着大范围水土保持措施工程的实施，黄土高原下垫面环境发生显著变化，改变了降雨径流关系。水保措施增加了下垫面植被盖度，意味着黄河中游传统的超渗产流区向蓄满产流或超渗-蓄满机制共存过渡；淤地坝在其生命周期内的不同年份，对汇流的“间歇阻断”作用存在显著差异。黄河中游水沙变化现象的背后，隐含着该地区原有的产汇流机理已发生改变。但目前大部分黄河水沙变化研究多侧重于从宏观上揭示水保措施的拦洪蓄沙机制，计算减水减沙效益，而较少涉及对水保措施综合治理条件下产汇流演变机理的研究。因此，对水保措施作用下产汇流机理科学问题认识的突破是提高黄河中游干旱半干旱区水文预报水平的理论基石，开展深入研究具有重要科学意义。.本项目通过开展水保措施的降雨产流阈值效应研究，建立了一种兼顾不同水保措施扰动下“复合”产流特点、更切合实际的普适“统一”产流模式；结合“网格水滴”汇流方法，构建了变动饱和带分布式水文模型，为黄河中游干旱半干旱流域洪水预报预警提供有力工具。主要成果包括：（1）揭示水保试验径流场土壤下渗特征。分析水土保持措施径流场不同试验项目下降雨-下渗资料，研究不同场次降雨设置不同试验项目条件下，各径流场径流、泥沙以及土壤含水率的响应，挖掘不同水保措施条件下减水减沙和土壤下渗的特征。（2）提出淤地坝和梯田拦蓄作用下的降雨产流阈值估算公式。在梯田减水机制研究方面，引入梯田占梁峁坡面积比，考虑水平梯田有埂/无埂及梯田质量情况，建立了水平梯田作用下的降雨产流阈值计算公式。在淤地坝减水机制研究方面，考虑已经淤平后作为农地利用的坝地、仍在拦洪时期淤地坝这两部分减洪量，推导了淤地坝拦蓄作用下的降雨产流阈值计算公式。（3）建立了基于变动饱和带产流模式和网格水滴汇流方法的分布式产汇流模型。综合RIBS模型中的变动饱和带产流模式和网格水滴汇流方法，构建基于单元网格剖分结构的分布式产汇流模型；这种新型产流模式有别于传统的蓄满-超渗两种产流机制水平向或垂向组合方式，避免人为设定某种产流机制的主观性，因而更接近真实的产流过程。（4）提出了基于“野外水文实验+实际流域率定”的参数确定方法。结合野外入渗试验和参数敏感性分析，建立地表饱和水力传导度和饱和水力传导度随深度衰减系数2个敏感性产流参数与地形参数、土壤类型数据的定量统计关系，利用野外坡面流观测试验确定坡面汇流参数，并在多个实际流域进行应用验证。