Preface. In coastal areas flooding is likely to be caused from groundwater rise because as sea levels rise, they won’t only move inland, flooding low-lying land near the shore; but also push water up from the saltwater water table, on top of which is a layer of lighter fresh water. As the salt water rises with rising seas, it will push this fresh water upward. In low-lying areas, that water may emerge from the ground.
The consequences are that water will leach inside homes through basement cracks. Toilets may become chronically backed up. Raw sewage may seep through manholes. Brackish water will corrode sewer and water pipes and inundate building foundations. And most hazardous of all, water percolating upward may flow through contaminants buried in the soil, spreading them underground and eventually releasing them into people’s homes. The coup de grace will be the earthquakes, which, when they strike, may liquefy the entire toxic mess, pushing it toward the surface.
The result will be that in places like Oakland, flooding will occur not just at the shoreline, but inland in areas once considered safe from sea level rise. The threat it poses can’t be neutralized with the usual strategy: physical structures that keep the sea at bay. No matter how many seawalls we build, many experts say, groundwater can still gurgle up from below, potentially turning large swaths of the densely populated shoreline around the Bay into unwanted, unplanned, possibly toxic wetlands.
Grace Mitchell Tada. March 25, 2019. The Sea Beneath Us Sea level rise has a gotcha-from- behind twin: rising groundwater. It’s already here. And some experts maintain, we’re not ready for it. Bay Nature
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