Fresh groundwater resources in a large sand replenishment

The anticipation of sea-level rise and increases in extreme weather conditions has led to the initiation of an innovative coastal management project called the Sand Engine. In this pilot project a large volume of sand (21.5 million m(3)) - also called sand replenishment or nourishment - was placed on the Dutch coast. The intention is that the sand is redistributed by wind, current, and tide, reinforcing local coastal defence structures and leading to a unique, dynamic environment. In this study we investigated the potential effect of the long-term morphological evolution of the large sand replenishment and climate change on fresh groundwater resources. The potential effects on the local groundwater system were quantified with a calibrated three-dimensional (3-D) groundwater model, in which both variable-density groundwater flow and salt transport were simulated. Model simulations showed that the long-term morphological evolution of the Sand Engine results in a substantial growth of fresh groundwater resources, in all adopted climate change scenarios. Thus, the application of a local sand replenishment could provide coastal areas the opportunity to combine coastal protection with an increase of the local fresh groundwater availability. Mekong Delta (Vietnam) and the Ganges-Brahmaputra delta (Bangladesh), are already frequently subjected to extensive floods, leading to considerable economic losses, property damage, and in severe cases loss of life (Few and Matthies, 2006; de Sherbinin et al., 2011; UNDP, 2004). In addition, many ecosystems and inhabitants of deltas are threatened as a result of high subsidence rates, over-exploitation of fresh groundwater resources, and contamination of coastal aquifers (Crain et al., 2009; de Sherbinin et al., 2011; Syvitski et al., 2009; UNDP, 2004). Sea-level rise and storm surges will enhance the pressure on these coastal regions (Kooi et al., 2000; Yang et al., 2013, 2015), and will likely exacerbate the loss of agricultural land, damage of ecosystems and the salinization of fresh groundwater resources (Hoggart et al., 2014; Nicholls, 2010; Oude Essink et al., 2010; Wong et al., 2014).