The world’s coastlines are facing unprecedented change due to sea level rise. While this may be highly visible in many cases as the sea swallows land, roads, buildings, and other infrastructure, major and potentially disruptive changes will also be happening in the unseen subsurface. The threat is most significant in highly developed urban areas. As the sea rises, coastal water tables rise too, flooding foundations, buried utilities, and other subsurface infrastructure, and increasing surface flooding by reducing the amount of infiltrating rainfall that can be stored. Rising seas will increase saltwater intrusion into coastal areas, with potentially devastating corrosion impacts on foundations and other buried infrastructure. Existing saltwater intrusion monitoring systems in some areas are designed to provide early warning protection for drinking water well fields and typically do not provide information at the needed locations or scales on water and saltwater conditions beneath often highly developed barrier island and coastal bay shore areas.