雅鲁藏布江典型流域地下水形成机理与演变预测

Groundwater is a primary water resource contributing to runoff in the Yarlung Tsangpo watershed. However, due to multiple contribution sources from rainfall, ice and snow melting and frozen soils, and complex topography and geology, groundwater cycle of recharge, storage and discharge presents significantly spatial and temporal heterogeneous characteristics. In this study, we selected two typical watersheds with different percentages of groundwater contribution (Nianchu River and Lhasa River contributed mainly by groundwater and precipitation, respectively). To analyze various sources of groundwater recharge and cycle characteristics, the project will be executed based collecting information of meteorological, hydrological, hydrogeological data, and hydrological experiment and detail observations, as well as combining methods of hydrology, hydrogeology, geochemistry and geophysics. We will divide watershed units according to hydrological response units coupling with hydrogeological units to represent regional characteristics of watershed groundwater cycle and develop hydrological model coupling with groundwater model for simulation and prediction of groundwater recharge, movement and discharge. The study will reveal mechanism of groundwater cycle and quantify proportion of groundwater contribution to the total runoff in the study watersheds. Our study will offer scientific supports for revealing runoff change in the region.

地下水是雅鲁藏布江径流重要补给来源，受雨水、冰川、积雪和冻土融水等多水源补给，加之复杂的地形和地质条件影响，地下水补径排循环具有显著的时空变异特性。本项目以雅鲁藏布江两个不同地下径流比例的流域（地下水补给为主的年楚河、雨水补给为主的拉萨河流域）为例，在详细调查和收集气象、水文、水文地质等资料基础上，结合典型地貌单元水文实验和强化观测，综合利用水文学、水文地质学、地球化学、地球物理等方法，解析地下水补给来源及循环特征；构建综合表征地表水文响应与地下水文地质特征相嵌套的控制单元，创建适用于研究区地下水补径排模拟和预测的地表水与地下水耦合模型，揭示研究区地下水补径排循环机理，定量分析地下水补给对河川径流的贡献，为揭示该地区径流演变规律提供科学支撑。

针对雅鲁藏布江以及两种不同地下径流比例的典型流域（年楚河、拉萨河流域），围绕多水源补给以及浅深层地下水补径排循环特征辨识、不同气候区水文与水文地质单元参数化分析、流域地下水演变对气候变化的响应机理三个关键科学问题，系统收集雅江流域上世纪80年代以来气候、水文、水文地质等资料，开展了不同水源（降雨、降雪、冰川和冻土融水多补给源，以及地表径流、浅深层地下径流多径流成分同位素和水化学分析，创建了高寒山区水文-温度-同位素和水化学信息相结合的多补给源以及多径流成分分析方法、模拟与预测模型。阐明了雅江流域上世纪80年代以来暖湿化冻融调蓄作用减弱，地表和地下径流比例增加，导致径流退水的非线性增强、稳定性减弱演变机理；通过对浅层潜水和深层承压水水龄和更新速率分析，揭示了浅深层地下水循环特征。发现了雅江中游深大断裂带水文、水化学和同位素异常现象与巨量的地下水补给有关，量化了深循环地下水资源量及其对径流的影响程度。