HYDROLOGICAL PROCESSES Hydrol. Process. 21, 2794–2806 (2007) Published online 14 March 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.6497 Simulated groundwater interaction with rivers and springs in the Heihe river basin Li-Tang Hu, 1 * Chong-Xi Chen, 2 Jiu Jimmy Jiao 3 and Zhong-Jing Wang 1 1 Institute of Hydrology and Water Resources, Department of Civil Engineering, Tsinghua University, Beijing, P.R. China 2 Institute of Environmental Geology, China University of Geosciences, Wuhan, P.R. China 3 Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China Abstract: Surface water and groundwater in the Heihe river basin of China are interconnected and the pattern of water resources exploitation has a direct effect on the interaction of groundwater and surface water, especially on a downstream oasis. A three- dimensional groundwater flow simulation model with eight model layers was established to simulate the regional groundwater flow in the multilayered aquifer system and the interaction among the rivers, springs, and groundwater. The model was calibrated not only with historical water levels but also with the investigated baseflow and spring flux. The simulation results of the numerical model match reasonably well with the observed groundwater levels, baseflow to rivers, and spring flux. The numerical simulation also demonstrates that the hydraulic connection between the river and the aquifers has transferred from the coupling to decoupling at some reaches. It is suggested that there is a vital need to reduce groundwater withdrawal and to rationalize the use of both groundwater and surface water in order to maintain sustainable development in the study area. Copyright  2007 John Wiley & Sons, Ltd. KEY WORDS numerical simulation; groundwater/surface-water relations; groundwater flow; arid regions; springs Received 11 January 2006; Accepted 16 June 2006 INTRODUCTION The middle reaches of the Heihe river basin are located in the middle section of the Hexi corridor in China, and were once part of the famous ‘silk route’ between China and the West during the period of the Han dynasty. With the intensity of human activities, the demand for water, especially for agricultural purposes, has increased rapidly in recent times, and both surface water (including rivers and springs) and groundwater have been exploited. The pattern of water resources exploitation has had a direct impact on the area of the delta oasis downstream of the Heihe river basin, where the Heihe River is the main source of recharge. Interactions between surface water and groundwater have gained more and more attention (Sear et al., 1999; Sophocleous, 2002; Rushton, 2003). A care- ful study of the dynamic interaction between surface water and groundwater will provide some guidelines for reasonable water resources exploitation and preven- tion of regional ecological environment from further degradation. In the study area, groundwater may discharge directly into rivers or discharge in the form of springs, which then join rivers. A spring is a natural resurgence of ground- water and can provide important information that allows *Correspondence to: Li-Tang Hu, Institute of Hydrology and Water Resources, Department of Civil Engineering, Tsinghua University, Bei- jing, P.R. China. E-mail: hulitang@tsinghua.org.cn for better understanding of the hydrogeological condi- tions. Springs can be classified into gravity springs and artesian springs according to the characteristics of the source aquifer. A key issue in this study is how to repre- sent interaction between groundwater, rivers, and springs numerically in the model. Springs have been widely stud- ied by previous researchers using various approaches, which include analytical methods (Atkinson, 1977; Bhar and Mishra, 1997; Swanson and Bahr, 2004), statistical analysis (Jian et al., 1998; Carol and John, 2000) and numerical modeling (Chen, 1995; Hunt, 2003; Swanson and Bahr, 2004). The analytical method is of limited use because it is usually under very strict assumptions. The statistical analysis is to establish the correlation func- tion among factors affecting spring flux. The relationship may be linear (Jian et al., 1998) or non-linear (Carol and John, 2000). In the numerical model, a spring could be treated as prescribed head boundary (Chen, 1995), which treats the elevation of the spring outlet as ground- water head, flux boundary or drain (Hunt and Steuer, 2001; Swanson and Bahr, 2004). When springs are treated as flux boundary, we need to specify the flux before the simulation, while if springs are treated as drains, it could be time consuming to solve the associated non- linear equation. A regional hydrogeological system is always heterogeneous. When spring flow is involved, especially in a karst aquifer system, flow in the spring vent can be non-Darcian. Chen (1995); Chen and Jiao (1999) presented an equivalent hydraulic conductivity (EHC) approach to integrate groundwater flow in porous media, fractures, and conduits (pipe flows). Details of Copyright  2007 John Wiley & Sons, Ltd.