A Rapid Assessment Method to Identify Potential Groundwater Flooding Hotspots as Sea Levels Rise in Coastal Cities

Ellen Plane,Christine May,Kristina Hill

doi:10.3390/w11112228

Abstract

Sea level rise (SLR) will cause shallow unconfined coastal aquifers to rise. Rising groundwater can emerge as surface flooding and impact buried infrastructure, soil behavior, human health, and nearshore ecosystems. Higher groundwater can also reduce infiltration rates for stormwater, adding to surface flooding problems. Levees and seawalls may not prevent these impacts. Pumping may accelerate land subsidence rates, thereby exacerbating flooding problems associated with SLR. Public agencies at all jurisdiction levels will need information regarding where groundwater impacts are likely to occur for development and infrastructure planning, as extreme precipitation events combine with SLR to drive more frequent flooding. We used empirical depth-to-water data and a digital elevation model of the San Francisco Bay Area to construct an interpolated surface of estimated minimum depth-to-water for 489 square kilometers along the San Francisco Bay shoreline. This rapid assessment approach identified key locations where more rigorous data collection and dynamic modeling is needed to identify risks and prevent impacts to health, buildings, and infrastructure, and develop adaptation strategies for SLR.

Highlights

Sea levels are rising over most of the world’s coastlines, and the rate of relative sea level rise (SLR) is projected to accelerate [1]
This eventually results in the emergence of groundwater as surface flooding, and increases surface discharges of streams supplied by groundwater [2]
Using the conservative assumption of a linear relationship between SLR and shallow, unconfined groundwater depth within one kilometer of the shore, we showed that many densely developed areas are at risk from rising and even emergent groundwater as the sea level rises

Summary

Introduction

Sea levels are rising over most of the world’s coastlines, and the rate of relative sea level rise (SLR) is projected to accelerate [1]. Shallow saline aquifers and unconfined freshwater aquifers with a direct saltwater interface (i.e., freshwater floating atop higher-density seawater) are affected by tidal fluctuation These aquifers rise and fall with the tides, and the effects decrease exponentially farther inland [3,4,5]. In “flux-controlled” systems, where the rate of groundwater discharge is constant as the sea level rises, SLR causes landward migration of the saltwater toe, otherwise known as saltwater intrusion [6,7]. This saltwater intrusion causes a lift in the level of the overlying freshwater [8]. This eventually results in the emergence of groundwater as surface flooding, and increases surface discharges of streams supplied by groundwater [2]

Methods

Results

Discussion

Conclusion