干涸河道治理工程中，获取河水补给地下水的侧向水力梯度至关重要，以永定河生态补水工程平原南段为研究区，运用垂直于河道的横断面监测法、地下水丘分析法、注水试验入渗面分析法研究侧向水力梯度。通过上述方法获取了永定河平原南段卵砾石层、中细砂层、粉细砂层中河水补给地下水的侧向水力梯度分别为28.6‰～3.7‰，10.7%～3.3%，6.7%～16.7%，说明在中细砂和粉细砂场区生态补水对地下水的影响范围有限。利用粉细砂场区侧向水力梯度估算了生态补水对地下水的影响范围，结果与实际影响范围接近。该研究有助于进一步分析河水和地下水的水力联系，对干涸河道治理具有重要现实意义。

River ecological water replenishment was very important for river recovery projects, leakage problem and its impact on underground water limited water resource scheduling and restoration of ecological zones. One of the difficulties lay in the unknown lateral hydraulic gradient for river ecological water replenishment, and there is very little existing research. Therefore, obtaining the lateral hydraulic gradient under different geological conditions had practical significance for studying the lateral hydraulic connection between surface water and groundwater in eco-hydraulic engineering, and also had important reference value for studying the combined numerical simulation of surface water and groundwater. The research took a certain section of the Yongding River as the research area for river ecological water replenishment. Basic data was obtained through long-term observation of groundwater level, measurement of surface water level, improvement of seepage tests to conduct infiltration surface analysis, geological exploration and drilling, Data organization and drawing was carried out using AutoCAD, Surfer, and GIS technic. The lateral hydraulic gradient was obtained using cross-sectional monitoring methods by perpendicular to the river, groundwater mound analysis, and water seepage tests infiltration surface analysis methods. In addition, it was also carried out that continuous monitoring of the water level dynamics of groundwater and confined water during river ecological water replenishment period in the research area. The research showed that using the cross-sectional monitoring method by perpendicular to the river channel, the lateral hydraulic gradients of groundwater recharge from river water in the gravel layer and fine sand layer were provided, with values of 28.6 ‰ to 3.7 ‰ and 10.7% to 3.3%, respectively. By using cross-sectional monitoring method, groundwater mound analysis, and infiltration surface analysis of water seepage test, the lateral hydraulic gradient from river water in the fine sand layer was obtained to be 0.07% to 2.8%, 0.33% to 6.8%, and 6.7% to 16.7%, respectively. Because the groundwater level monitored in the cross-section of the fine sand area was the later data of the first river ecological water replenishment of the Yongding River, so it was possible that the hydraulic connection between the river water and groundwater was disconnected, and the obtained lateral hydraulic gradient value was too small to be used. The lateral hydraulic gradient in the fine sand layer was greater than that in the medium and fine sand and pebble layers, and the lateral hydraulic gradient in the fine sand layer through the analysis of the infiltration surface of water seepage tests was consistent with common sense. Therefore, analysis data of the infiltration surface of water seepage test can be used as the lateral hydraulic gradient for the initial infiltration of the fine sand layer that was to say 6.7% to 16.7%. In addition, it was found that both groundwater and confined water in the fine sand field area of the downstream based on river ecological water replenishment had response in water level, with a significant increase in groundwater level within a distance of 50-350 meters from the riverbank. The confined water level responded slightly earlier than the groundwater level. Previous studies had shown that the ecological replenishment of fine sand fields in the study area had an impact range of approximately 200 meters on groundwater levels, according to parameters: the lateral hydraulic gradient 6.7% in the fine sand formation, the head difference 10m between river water and regional groundwater, that calculated impact range was 150m. The both results were relatively close. This research obtained the lateral hydraulic gradient in the gravel layer, medium fine sand layer, and fine sand layer; it found that the surface water of the Yongding River was closely related to groundwater. With the continuous river ecological water replenishment, the initial lateral hydraulic gradient was relatively large, and then gradually decays to a stable state. The impact of river ecological water replenishment on groundwater was limited in areas with fine particles such as fine sand.

国家自然科学基金项目（面上项目，重点项目，重大项目）51979285