hydrology Review Surface and Groundwater Interactions: A Review of Coupling Strategies in Detailed Domain Models Arefin Haque 1, Amgad Salama 1, Kei Lo 2 and Peng Wu 1,* 1 Environmental Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, Regina, SK S4S 0A2, Canada; [email protected] (A.H.); [email protected] (A.S.) 2 Hydrology and Groundwater Services, Saskatchewan Water Security Agency, Moose Jaw, SK S6H 7X9, Canada; [email protected] * Correspondence: [email protected] Abstract: In groundwater numerical simulations, the interactions between surface and groundwater have received great attention due to difficulties related to their validation and calibration due to the dynamic exchange occurring at the soil–water interface. The interaction is complex at small scales. However, at larger scales, the interaction is even more complicated, and has never been fully addressed. A clear understanding of the coupling strategies between the surface and groundwater is essential in order to develop numerical models for successful simulations. In the present review, two of the most commonly used coupling strategies in detailed domain models—namely, fully-coupled and loosely-coupled techniques—are reviewed and compared. The advantages and limitations of each modelling scheme are discussed. This review highlights the strategies to be considered in the development of groundwater flow models that are representative of real-world conditions between surface and groundwater interactions at regional scales. Keywords: coupling strategies; groundwater; interaction; fully coupled scheme; loosely coupled scheme Citation: Haque, A.; Salama, A.; Lo, K.; Wu, P. Surface and Groundwater Interactions: A Review of Coupling Strategies in Detailed Domain 1. Introduction Models. Hydrology 2021, 8, 35. Water security is an emergent issue in the world due to climate change and variability, https://doi.org/10.3390/ and increasing water demands due to population growth and economic development [1]. hydrology8010035 Both surface water and groundwater are, inevitably, resources that are needed in order to meet future water demands. Groundwater is widely used in the national economies Received: 30 December 2020 of many countries for different purposes, such as potable and industrial water supply, Accepted: 14 February 2021 irrigation, and mineral water. Fresh groundwater is of particular importance as the main Published: 23 February 2021 source of public water in the domestic and drinking water balance. To date, groundwater is the main source of potable water in most European countries and in the United States, Publisher’s Note: MDPI stays neutral which accounts for 75% of municipal water supply system [2]. Irrigation has grown rapidly with regard to jurisdictional claims in over the past 50 years, and approximately 40% of the irrigated regions of the world are pre- published maps and institutional affil- iations. dominantly governed by groundwater resource [3]. However, in recent years, the depletion of groundwater has become a concern due to overexploitation. A greater understanding is needed to better manage the limited water resources, especially in drought-prone areas. There is a need to better understand the interactions between groundwater and surface wa- ter, which is fundamentally an integrated feature in the hydrologic cycle. These interactions Copyright: © 2021 by the authors. could be influenced by both natural and anthropogenic processes [4]. Recently, research has Licensee MDPI, Basel, Switzerland. focused on the proper selection of models that accounts for surface and groundwater inter- This article is an open access article actions coupled into a single framework. However, there are many restrictions associated distributed under the terms and conditions of the Creative Commons with this approach. There are considerable fluctuations of surface and groundwater inter- Attribution (CC BY) license (https:// actions at the soil–water interface due to the heterogeneous nature of the porous medium creativecommons.org/licenses/by/ with time, along with the variabilities due to climate change. The diversity of aquifer types, 4.0/). along with recharge and groundwater flow conditions, and the extensive range of river Hydrology 2021, 8, 35. https://doi.org/10.3390/hydrology8010035 https://www.mdpi.com/journal/hydrology Hydrology 2021, 8, x FOR PEER REVIEW 2 of 16 diversity of aquifer types, along with recharge and groundwater flow conditions, and the extensive range of river flow circumstances provide the ingredients for a complex system of interactions, which heightens the need for robust modelling and solution methodolo- gies [5]. Surface water models are being used to understand surface water systems by includ- Hydrology 2021ing, 8 ,possible 35 deviations due to both natural and human influences. The interrelation and2 of 16 coupling among various subsystems of the hydrological cycle has been noted by many pioneer researchers in the process of the physical and mathematical description of the flow processes [6].flow The circumstances first physically-based provide the ingredients and coupled for a complex model, system Système of interactions, Hydrologique which Européen (SHE), washeightens developed the need primarily for robustmodelling based on and fundamentals solution methodologies of surface [5]. water flow. The United States GeologicalSurface water Survey models (USGS) are being PRMS used (Precipitation-Runoff to understand surface water Modelling systems by Sys- includ- tem) and Nationaling Oceanic possible and deviations Atmospheric due to both Administration natural and human (NOAA)’s influences. National The interrelation Weather and coupling among various subsystems of the hydrological cycle has been noted by many Service models [7]pioneer are the researchers recent developments in the process ofof thesurface physical water and models. mathematical The groundwater description of the flow models haveflow the processesability to [ 6simulate]. The first predicted physically-based impacts and from coupled over-exploitation, model, Système Hydrologique to sim- ulate the fate andEurop transportéen (SHE), of wasa contaminate developed primarily plume, based and onto fundamentalsforecast the ofvariation surface water of the flow. groundwater levelsThe Unitedwith Statestime Geologicaldue to climatic Survey (USGS) variability. PRMS (Precipitation-Runoff However, the traditional Modelling Sys- tem) and National Oceanic and Atmospheric Administration (NOAA)’s National Weather groundwater flowService models models neglect [7] are the the incorporat recent developmentsion of surface of surface water water flux models. into The the groundwater subsur- face environment.flow MikeSHE models have and the SHETRAN ability to simulate were further predicted developed impacts from and over-exploitation, applied with to both surface and simulategroundwater the fate flow and transport[8–10]. of a contaminate plume, and to forecast the variation of From the literature,the groundwater it has been levels noticed with time that due the to modelling climatic variability. and simulation However, of the ground- traditional groundwater flow models neglect the incorporation of surface water flux into the subsur- water and surface water interaction have been conducted by many researchers [11–14]. face environment. MikeSHE and SHETRAN were further developed and applied with Multiple factors haveboth surfacebeen reported and groundwater that co flowuld [influence8–10]. the interaction between ground and surface water, suchFrom as the hydro-climatic literature, it has variables; been noticed physiographic that the modelling structure; and simulation differences of ground- in the head betweenwater the and catchment surface water surface interaction water have and been conductedgroundwater; by many and researchers the surface [11–14 and]. Mul- groundwater flowtiple geometry factors have [15,16]. been reportedThe mo thatdeling could of influence flows and the interactiontransport betweenphenomena ground as and surface water, such as hydro-climatic variables; physiographic structure; differences in the discrete groundwaterhead betweensystems the has catchment been achieved surface water well and by groundwater; relatively and simpler the surface approaches and ground- [15,17]. However,water the modelling flow geometry process [15,16]. is The complicated modeling of flowsby the and inclusion transport phenomenaof surface as water discrete and groundwatergroundwater interaction. systems Ever-present has been achievedinteractions well bybetween relatively groundwater simpler approaches and sur- [15,17]. face water are a concernHowever, due the modellingto the continuous process is complicatedflow of groundwater by the inclusion into of rivers surface [5]. water The and groundwater interaction. Ever-present interactions between groundwater and surface wa- integration of groundwater and surface water interaction could be classified in many dif- ter are a concern due to the continuous flow of groundwater into rivers [5]. The integration ferent ways. Figureof groundwater 1 illustrates and a surface schematic water interaction of the different could be classifiedavailable in manymodelling different ap- ways. proaches. It servesFigure as the1 illustrates foundation a schematic and framework of the different for the available present modelling review. approaches. The objectives It serves of the present reviewas the are foundation to compare and framework the coup forling