A saturated–unsaturated coupling model for groundwater flowing into seepage wells: a modeling study for groundwater development in river basins

Xianmin Ke,Haiyang Hu,Jinlong Li,Xiangdong Xu,Wei Wang

doi:10.1007/s12665-021-10035-8

Abstract

As a major and popular groundwater extraction structure, seepage wells are often used to transfer river water into aquifers for harvesting water resources. It can help ameliorate the imbalance between supply and demand, in particular, in areas of water scarcity. Large drawdowns due to pumping may cause the river to disconnect from the groundwater and form an unsaturated zone, which seriously affects the efficiency of seepage wells. However, most of the current models of extraction structures of non-tube wells account for only saturated flow and do not consider unsaturated conditions. To address this limitation, a saturated–unsaturated coupling model was developed using the exchange flow rate between the well pipe and the aquifer as the coupling point. Moreover, the model was evaluated with physical simulation test data. The statistical results indicated that the model could estimate the drawdown and pumping rate well with root-mean-square deviations of 0.0114 m and 0.0079 L s−1, respectively, for a river with strong leakage capacity; and 0.0129 m and 0.0099 L s−1, respectively, for a river with weak leakage capacity. The critical drawdown, where the river disconnects from the aquifer, as well as variations of the unsaturated zone, was also discussed. The present study provides important information for the design of seepage wells with reasonable drawdown, while being able to predict the potential water yield, and at the same time help protect the groundwater environment.

Highlights

Groundwater is one of the most important available water resources (Qiao et al, 2020; Wang et al, 2020) and is often harvested from aquifers in river basins where a huge population often resides (Li and Qian, 2013; Li et al, 2014)
For the simulated river with a strong leakage capacity, the flow rate increased linearly with the increase of the drawdown in the shaft, which indicated that the water yield of the seepage wells can be guaranteed due to a sufficient recharge source
This was due to the limited recharge capacity of the river preventing the aquifer from being recharged quickly enough, which led to the river being disconnected from the groundwater, thereby forming an unsaturated zone

Summary

Introduction

Groundwater is one of the most important available water resources (Qiao et al, 2020; Wang et al, 2020) and is often harvested from aquifers in river basins where a huge population often resides (Li and Qian, 2013; Li et al, 2014). Compared with a traditional well, seepage wells and other similar water extraction structures have many advantages, such as high production, low consumption, convenient management, and relatively low cost of water supply It is widely used as a means to increase water resources (Ameli and Craig, 2018; Maroney and Rehmann, 2017; Wu et al, 2019). It may lead to a disconnection between the groundwater aquifer and an associated river, thereby forming an unsaturated zone (Brunner et al, 2011; Cognac and Ronayne, 2020; Glennon, 2007; Sun, 2017; Wang et al, 2009; Xie et al, 2015) In this way, the water yield would not increase significantly, but the water extraction efficiency would decrease when the unsaturated zone appears (Chang et al, 2019 )

Objectives

Methods

Results

Conclusion