West Honolulu Watershed Study - Final Report - Prepared for

West Honolulu Watershed Study FINAL REPORT
Kalihi Streambank Stabilization Project (Page 1 of 2) Project 16
Category Project Type Participating Agencies
Surface Water
Quality
PROJECT DFM; DLNR-Engineering Division, DAR; COE
A. Problem Statement
The stream banks along the lower reaches of Kalihi Stream have not been stabilized and are below capacity
for the 100-year flood. Erosion of these unprotected banks contributes to sediment build-up near the mouth
of Kalihi Stream. At the mouth of Kalihi stream, the banks are overgrown with mangrove, which reduces
channel capacity and destroys the natural ecosystem.
B. Project Background
The lower reaches of Kalihi Stream are in the flood zone because of inadequate channel capacity to convey
storm waters of the 100-year flood. This reach of the stream is also in an industrial section of the city, and
visual surveys of the unstabilized section reveal a condition of neglect and misuse. Eroding banks of Kalihi
Stream contribute to stream sedimentation near the mouth of the stream. Mangrove have established and
overtaken the banks of Kalihi Stream near the mouth, which reduces channel capacity in the vicinity of the
restrictive bridge openings, further increasing the flood hazard. A 1975 COE report recommended 8,400 feet
of channel improvements to the lower reaches of Kalihi Stream at a cost of about $7 million, which consisted
of a system of levees and concrete-lined rectangular and trapezoidal sections with rip-rap side slopes. The
project was not implemented due to a low benefit-to-cost ratio.
C. Project Objectives
The objective of this project is to stabilize the banks of Kalihi Stream between the Bannister Street area and
the receiving waters of Ke‘ehi Lagoon, a stretch of approximately 3/4 miles. The project will incorporate the
findings and recommendations in the West Honolulu Watershed Expanded Trails Study (Project 03). Reasons
for restoring Kalihi Stream include native aquatic species habitat enhancement, increased pedestrian and
bicycle access, and overall beautification of Kalihi Stream.
Questions to be considered in this project include:
ο What successful streambank stabilization projects could serve as a model for Kalihi Stream?
ο What are the policy requirements to implement streambank stabilization?
ο What water quality, native species habitat, and public access considerations are to be incorporated
into streambank stabilization?
ο How will flood control designs be incorporated into the streambank stabilization project?
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