VNR: Multiple flooding sources threaten Honolulu’s infrastructure

University of Hawaiʻi at Mānoa
Shellie Habel, (808) 286-2586
Coastal Geologist and Extension Agent , School of Ocean and Earth Science and Technology
Posted: May 4, 2020

Link to video and sound (details below):

WHAT: In the next few decades, sea-level rise will likely cause an increase in flooding in Honolulu’s urban core primarily caused by groundwater inundation, according to University of Hawaiʻi at Mānoa researchers from the School of Ocean and Earth Science and Technology (SOEST).  

WHO: Shellie Habel, lead author of the study and coastal geologist and extension agent with the UH Sea Grant College Program, and Chip Fletcher, co-author and SOEST Associate Dean, and their team, in partnership with Hawaii Community Foundation.

WHERE: Honolulu, Hawaiʻi

HOW: The researchers developed a method that identified the various flood types—groundwater inundation, reverse municipal drainage and direct marine inundation, which represents the least extensive at only 3 percent. Flood maps were produced by simulating flood locations and depths generated by each and overlapping the simulations to identify the most vulnerable areas over the coming decades.

WHY: To highlight the need to readjust the thinking regarding the flooding that accompanies sea level rise and encourage the implementation of effective flood management strategies. Many people think that sea-level rise can be mitigated by seawalls, but seawalls will not stop groundwater inundation. 


  • The flooding impacts were found to be widespread among Honolulu’s heavily densified primary urban center.

  • Seawalls will not stop groundwater flooding, the only response possible is to design for water, or abandon the area projected to be impacted.

  • Colleagues at the UH Sea Level Center developed a statistical model that considers predicted tide and projected magnitudes of local sea-level rise to establish the frequency with which flooding is likely to occur in given locations.

  • With flood simulations, the research team assessed critical infrastructure that is likely to fail and cause direct impacts, such as dangerous or impassable roadways, storm drainage inlets likely to fail or act as pathways for additional flooding, and non-functional or flooded cesspools.

  • In partnership with the Honolulu Board of Water Supply, UH, Hawai‘i Sea Grant and other stakeholders, the authors plan to develop a real-time coastal groundwater monitoring network. 

  • Data collected through the monitoring network will help improve the capabilities of the modeling such as the ability to incorporate the effects of extreme rainfall, and provide information that could inform the development of short-, mid- and long-term flood management strategies.

VIDEO BROLL: (1 minute, 26 seconds)

  • Flooding in Honolulu’s urban areas

  • Water coming up from drainage systems

  • Cars driving through flooded streets

  • Honolulu Harbor Tide Record


Shellie Habel, UH Sea Grant College Program, Coastal Geologist and Extension Agent (12 seconds)

“What this means for the future of Honolulu is that we need to consider each different type of flooding individually and really think about how we’re adapting to each one.”