Oʻahu officials put residents on edge Friday night after a county HNL Alert warned that Wahiawā Dam might be at risk of failing, with the potential for catastrophic flooding downstream. The alert told people in low-lying North Shore neighborhoods to head for higher ground and follow directions from local emergency crews as heavy rain marched across the island.
The warning went out at about 6:55 p.m. Friday as a post from the Hawaii Department of Transportation, which shared an update from the Oʻahu Department of Emergency Management. The message stated that “dam failure possible at WAHIAWA DAM” and included a map of evacuation zones, identifying areas downstream that could flood and urging residents in those zones to act immediately, according to Hawaii DOT on X.
Background on the dam
Wahiawā Dam, which impounds Lake Wilson and dates back to 1906, is classified by state engineers as a high-hazard structure and is rated in poor overall condition. State documents caution that a failure would likely result in loss of life and would place roughly 2,492 people and hundreds of parcels directly in the flow path, according to the Department of Land and Natural Resources.
How officials are watching the reservoir
To keep tabs on what the dam is doing in real time, the U.S. Geological Survey operates a gage at the Wahiawā Reservoir spillway that tracks lake levels and flows, according to USGS. That data feed is part of a multi-agency response as crews watch to see whether the reservoir is stabilizing or still rising during the storm.
Who was told to evacuate and what to do
The HNL Alert targeted communities downstream of the dam, including parts of Haleiwa and Waialua, warning residents to evacuate because “failure of the dam could result in catastrophic flooding,” per Hawaii DOT on X. Officials urged people in evacuation zones to move to higher ground, stay away from streams and low-lying roads, and follow all instructions from first responders…