Lower Hamakua Ditch - Waipio Valley Misc. Improvements

The Lower Hamakua Irrigation Ditch is a historic water system built during the sugar plantation era. Constructed in 1906, not only to irrigate sugar fields but also to help transport harvested cane to the mill for processing. The system extends roughly 26 miles and includes a combination of tunnels, flues used to control water flow, and open ditches lined with stone walls.
This project addressed chronic sediment buildup and debris blockage at the surface water intake and conveyance systems serving Waipio Valley, including Kawainui, Alakahi, Koiawe, and Waimea Valleys. Existing intake structures routinely filled with sand and debris, and horizontal grates became clogged with leaves and rock, restricting flow. Due to the remote terrain, the Department of Agriculture was required to access the sites by helicopter for frequent maintenance and manual cleaning. In addition, an existing tunnel conveying river water to downstream agricultural users had partially collapsed, disrupting water delivery.
EPI repaired the collapsed tunnel and modified the intake and conveyance structures to improve reliability and reduce maintenance. Intake grates were replaced with angled, self-cleaning grates designed to shed debris and minimize clogging, restoring consistent water conveyance and significantly reducing the need for helicopter-based maintenance.