Development of a Coastal Groundwater Monitoring Network in Honolulu's Primary Urban Center and Initial Observations

Groundwater inundation (GWI) is expected to produce some of Honolulu's most problematic sea level rise flooding owing to its ability to evade coastal barriers designed to mitigate surface-water inundation as it is lifted through the ground surface. Simulations of GWI that employ 3D numerical modeling (MODFLOW-2005) have been produced for the purpose of identifying urban infrastructure vulnerabilities. The simulations are valuable tools for use in resilience retrofitting, however the hydrologic model with which they were constructed is based on limited groundwater level datasets such that simulations represent only steady-state conditions of the water table. Through a partnership between the Honolulu Board of Water Supply and the University of Hawai'i, a groundwater monitoring network is being installed to collect data to improve these simulations and to improve current understanding of projected 21st century sea level rise, tides, and likely increases in extreme precipitation on the position of the water table across the Primary Urban Center of Honolulu. Here we will discuss initial observations including influence from recent heavy rainfall, high tides and swell events.