北方河流潜流带水交换变化机理与数值模拟

Surface water and groundwater are two interconnected components of one single resource and impacts on either of these components in the hyporheic zone, which will inevitably affect the quantity or quality of the other. Estimation of variability and dynamic mechanism of hyporheic water exchange is of critical importance in integrated management of groundwater and surface water bodies and in maintenance of ecosystem health of a river catchment. As a case study of the Weihe River, stream water and groundwater are inherently connected and water quality is strongly interacted. Therefore, the temporal and spatial patterns of water flux and its variation mechanism in the hporheic zone of the Weihe River are demonstrated. Firstly, the temperature profiles are measured by a simple thermal mapping method. Simultaneously, the hydraulic gradient and hydraulic conductivity are measrued using a falling head a two step falling-head permeameter test method. Also, the factors affecting hyporheic water flux are determined and anlyzed, respectively, Then, the hyporheic water flux is estimated by head-diffusion-advection equation. Furthermore, the spatial and seasonal variability patterns of the stream water and groundwater interaction are illustrated, and the dynamic mechanism casuing the the hyporheic water flux variation are analyzed and illustrated. Secondly, the USGS numerical heat transport model VS2DH is used to evaluate the thermal response of the streambed sediments to transient variation in surface water temperature and to simulate spatial and temperical transfer pattern of surface-ground water exchange in the hyporheic zone. Moreover,a three-dimoensional MODFLOW model based on GIS is used to simulate hyporheic water flux. On the basis of results from the mnumerical solution analyses, the transient vational patterns of hyporheci water exhange and flux can be illustrated. This study will be helpful for deepen understanding of hydrological processes of water exchange and its variational mechanism in the hyporheic zone and even to determine the transient variation of hyporheic water flux. It provides a theoretical approach for determination of stream water and ground water interaction, and even a scientific reference for controlling water pollution of both surface water and groundwater, and improving ecosystem healthy conditions of both waterway and catchment of a river.

正确认识河流潜流带河水与地下水交换变化的作用机理及其动态变化规律在维持河流健康以及全球水循环中起着十分重要的作用。本课题以河水与地下水水力联系密切，水质相互影响明显的北方河流-渭河作为研究背景，进行潜流带水交换的试验测试及其变化机理与数值模拟研究。采用以基于热扩散对流方程的温度梯度法为主导，并以基于达西定律的水力渗流试验为辅助的研究手段，分不同河段、不同时间同一研究点，对潜流带水交换进行测试、计算与分析，并对水交换的内在驱动因素做同步测试、观测与分析，揭示潜流带水交换时空变化特性，解析其影响机理。同时，采用MODFLOW与GIS相结合，借助VS2DH模型的技术方法，进行潜流带水交换关系及量值的数值模拟，试图揭示潜流带水交换的时空动态变化模式。本课题的研究，有利于深化潜流带水交换变化及其驱动与变化机理的的科学认识，将为河流-地下水系统的科学管理与持续利用、以及河流健康维护与修复提供理论依据。

正确认识河流潜流带水交换及其动态变化规律在维持河流健康起着十分重要的作用。本课题以河水与地下水水力联系密切渭河作为研究背景，进行潜流带水交换的试验测试、变化机理与数值模拟研究。取得的主要成果有：（1）采用温度梯度法为主，水力梯度法为辅，通过对河床温度和沉积物渗透系数现场试验测试以及水交换的计算，结合传统统计学方法和地统计学方法分析得出：水交换变化范围从78.47 mm/d到23.66mm/d。秋季大于其他季节，河流干流水交换量从上游到下降呈下降趋势等时空变异规律。（2）通过对影响潜流带水交换的相关因素的同步测量、观测与分析，揭示了潜流带水交换的影响因素及其作用机理。结果表明：沉积物属性包括渗透系数、中值粒径、孔隙度等对潜流带水交换影响具有显著的正相关性。河床河流形态对潜流交换具有较大的影响作用，弯曲河道与分叉河道中靠近侵蚀岸一侧的水交换量较大，而顺直河道靠近沉积岸的水交换量较大；沿着弯曲河岸两侧，河流曲率越大，水交换量越大；并且在河岸植被靠近河岸线且覆盖度较大的直河岸段，水交换量具有明显增大的趋势。（3）通过潜流带大型无脊椎动物调查与模拟实验，揭示了生物扰动对潜流带水交换的影响机理，生物扰动能改变沉积物的内部和表层结构、沉积物成分组成等，以此破坏或加强沉积物中细小颗粒物的阻塞，致使沉积物的渗透性能增强或减弱，从而对河流潜流带水交换产生显著性影响。（4）基于野外测试及室内模拟，解析了潜流带间隙水中污染物浓度的变化对水交换的响应机理。结果表明：上升流通量小于 400mm/d时，铵离子浓度随交换通量增大而增大，当大于 400mm/d时，随水交换量增加，铵根离子浓度降低，但重金属扩散通量与潜流带上升通量呈显著正相关性。（5）基于Modflow模型，采用Comsol Multiphysics软件，对潜流带水交换做了模拟分析。本研究成果，有利于深化潜流带水交换变化及其驱动与变化机理的的科学认识，为河流-地下水系统的科学管理与持续利用、以及河流健康维护与修复提供理论依据。