Geological Survey assesses risk levels of coastal areas

By Jan TenBruggencate
Advertiser Science Writer

The U.S. Geological Survey has produced a full-color report on the coastal hazards of the Hawaiian Islands.

The new report covers the coastline of all the main Hawaiian Islands except Kaho'olawe and Ni'ihau.

The authors say the report is meant to help assess the dangers of specific shoreline areas to avoid building expensive developments in danger zones.

"Our ultimate goal is to make the Hawaiian coast a safer place by educating the people of the state and their leaders about the hazardous nature of the environment," said co-author Bruce Richmond, a U.S. Geological Survey scientist. "The best way to avoid costly and dangerous mistakes in terms of lives and property is to avoid inappropriate development in the coastal zone."

For each section of coastline, the report has a color map with color-coded threat bars.

For Waikiki, there is a high tsunami danger, a moderate risk from stream flooding, a moderately low risk from high surf, a high risk of storm damage, a moderately high risk of erosion, a moderately low risk from sea-level change and a moderately high risk from volcanic or seismic events.

There is an overall assessment for each region, using a scale from 1 for low to 7 for high. Waikiki and Honolulu are a 5.

"The moderate to high overall hazard assessment for the Honolulu coastal zone is principally dictated by the low coastal slope, which is especially susceptible to damage resulting from tsunami, stream flooding, hurricane storm surge and seasonal high-wave flooding," the report says.

It says that since "Honolulu has yet to experience a direct hit from a major hurricane or tsunami, a complacency may exist among its inhabitants that hurricanes and tsunamis are not major threats to this coast."

The region is, in fact, extremely vulnerable to these threats, the report says.

Most of the Hilo area of the Big Island has a higher vulnerability rating, since many regions there are at moderate to high risk from nearly all the threats.

For those who may be confused about sea-level rise, in Hawai'i there are two factors at play. The sea is rising, but different Hawaiian islands are also subsiding or rising at different rates.

"This makes relative sea-level rise in Hilo (1.63 inches/decade) faster than on O'ahu (0.64 inches/decade) and Maui (0.96 inches /decade).

The new atlas is available for free online or for $38, plus shipping and handling, from the USGS Earth Science Information Center, at 1-888-ASK-USGS.