Overview
The ‘Īao Stream Flood Control Project (FCP) protects the town of Wailuku on Maui from damaging floods. The original project, completed by the U.S. Army Corps of Engineers (USACE) in 1981, includes a debris basin, diversion levees, and channel improvements along the lower 2.5 miles of the stream. The non-Federal sponsor is the County of Maui, Department of Public Works.
‘Īao Stream, also referred to as Wailuku River, flows from the Māuna Kahālāwai (West Maui Mountains) about six miles to Kahului Bay. Since construction, repeated high-flow events have eroded portions of the channel and levee toes (the base areas of the levee slopes). USACE and the County of Maui continue to work together to address these issues and sustain flood protection for the community.
This project reduces flood damages to the town of Wailuku. To date, the project has prevented more than $50 million in damages. The purpose of the ‘Īao Stream FCP is to address ongoing flood hazards caused by the long-term damage during repeated floods to the existing project structures since its construction completion and to provide the authorized level of reduced flood risk to Wailuku.
Current Phase & Schedule
The project is in Pre-construction Engineering and Design (PED), under a Design Agreement executed with the County of Maui on May 5, 2023. Planned milestones:
- Pre-construction Engineering & Design: 2024–2025
- Construction Contract Award: 2026
- Construction Complete: 2027
What We’re Building
The recommended plan focuses on three improvements that work with the river to reduce erosion and improve safety:
- Remove “Revetment X” (Concrete-Boulder Lining)
A past concrete-boulder lining narrowed and straightened the river, increasing velocities and erosion. Removing the remaining segments will widen the channel so flows can spread out and slow down, reducing stress on the right-bank levee and surrounding areas.
- Install a Pre-Formed Scour Hole (with a small drop structure)
The river's flow has eroded the area just past the concrete-lined reach, creating an unstable drop and deep hole. We will construct a Pre-Formed Scour Hole (like a shock absorber for the water) and a small drop structure. This engineered basin will safely absorb the water's energy, protecting the riverbed and preventing further erosion and cutting downstream.
- Stream Gage & Flood Warning System
An automated gage (water level) and an integrated alert system, coordinated with the County of Maui Emergency Management Agency, will provide real-time data and quicker warnings. In fast-rising storms, this system can improve evacuation times and community safety.
Community Benefits
- Helps reduce flood risk to Wailuku by addressing long-standing erosion hot spots.
- Lowers long-term maintenance needs by fixing underlying design deficiencies.
- Improves life-safety with faster, clearer flood warnings and better situational awareness.
Authorization & Ownership
- Authority: Section 203, Flood Control Act of 1968 (Public Law 90-483)
- Original Construction: Completed October 1981 by the U.S. Army Corps of Engineers
- Sponsor: County of Maui (Department of Public Works)
- Operations & Maintenance: Turned over to the County if Maui at completion; the Corps conducts joint inspections with the County to help ensure the project continues to perform as intended.