Impact of topography on groundwater salinization due to ocean surge inundation

Abstract

Sea‐level rise and increases in the frequency and intensity of ocean surges caused by climate change are likely to exacerbate adverse effects on low‐lying coastal areas. The landward flow of water during ocean surges introduces salt to surficial coastal aquifers and threatens groundwater resources. Coastal topographic features (e.g., ponds, dunes, barrier islands, and channels) likely have a strong impact on overwash and salinization processes, but are generally highly simplified in modeling studies. To understand topographic impacts on groundwater salinization, we modeled a theoretical overwash event and variable‐density groundwater flow and salt transport in 3‐D using the fully coupled surface and subsurface numerical simulator, HydroGeoSphere. The model simulates the coastal aquifer as an integrated system considering overland flow, coupled surface and subsurface exchange, variably saturated flow, and variable‐density groundwater flow. To represent various coastal landscape types, we simulated both synthetic fields and real‐world coastal topography from Delaware, USA. The groundwater salinization assessment suggested that the topographic connectivity promoting overland flow controls the volume of aquifer that is salinized. In contrast, the amount of water that can be stored in surface depressions determines the amount of seawater that infiltrates the subsurface and the time for seawater to flush from the aquifer. Our study suggests that topography has a significant impact on groundwater salinization due to ocean surge overwash, with important implications for coastal land management and groundwater vulnerability assessment.

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

“…In addition to effects of variable wave forcing, large episodic wave events where the coastal plain is overtopped and inundated by seawater have a significant and long lasting (order of years) influence on the flows and salinity distribution in a CUA [Anderson and Lauer, 2008;Smith et al, 2008;Santos et al, 2009a;Yang et al, 2013;Yu et al, 2016]. Yu et al [2016] showed numerically the important role of coastal topographic features in controlling the amount of seawater that infiltrates into the CUA when seawater inundation occurs and the length of the recovery time afterwards.…”

“…Yu et al [2016] showed numerically the important role of coastal topographic features in controlling the amount of seawater that infiltrates into the CUA when seawater inundation occurs and the length of the recovery time afterwards. Anderson and Lauer [2008] suggested that due to the long-lasting 23 effects, episodic overtopping events can be a major controlling factor for saltwater-freshwater mixing in STEs on micro-tidal barrier islands.…”

“…This is likely in part due to the challenges inherent in investigating irregular and longer period forcing via field experiments as well as the difficulties of disentangling the various forcing effects. Irregular forcing, particularly varying wave conditions and episodic events such as overland seawater inundation, may have a great impact on the salinity distribution, mixing and geochemical processes within a CUA due to potential large-scale salinization combined with the slow recovery (freshening) of the aquifer [Smith et al, 2008;Robinson et al, 2014;Yu et al, 2016]. Large-scale salinization of a CUA may also, for instance, lead to mobilization of legacy metals and organic contaminants, although these potential impacts have not been explored.…”

“…Understanding interactions between CUAs and the coastal ocean is critical for integrated resource management as these interactions control the exchange of water and chemicals across the land-ocean interface in both seaward and landward directions (Figure 1) [Leeks and Jarvie, 1998;Carabin and 6 Dassargues, 1999;Alongi et al, 2004;Newton and Mudge, 2005]. From a terrestrial perspective, CUA-ocean interactions are important because they affect the availability of fresh groundwater in coastal areas, which can be threatened by seawater intrusion Yu et al, 2016]. From a marine perspective, CUA-ocean interactions are important because they can impact coastal water quality and ecosystems due to the discharge of groundwater and associated chemicals to the coastal ocean [Moore, 2010].…”

Quantifying threats to groundwater resources in the Republic of Maldives Part II: Recovery from tsunami marine overwash events

“…Other studies have investigated the effect of aquifer salinization along coastal areas, although not specifically to atoll islands. Yu et al () also used the HydroGeoSphere model to study the effect of topographic connectivity in Delaware in the United States. Sixteen categories of topographic realizations were simulated to conclude that topographic connectivity (flat topography) promotes controls the volume of seawater salinizing the fresh groundwater.…”