The State of Hawaii Department of Transportation, Highways Division, Oahu District (DOT-HWYS) is actively implementing their Permanent Erosion Control Program by repairing eroded slopes along, and under, their Highways. Some of these eroded sites occur at underpasses where establishing vegetation is extremely difficult due to constant shading from the freeway, steep slopes, and poor soil conditions. At this site in Waipahu there was extreme soil erosion occurring under the H-1 freeway deck. The solution was the construction of a grouted angular stone surface, known as “riprap”, to provide permanent protection for the slope. For this technique, the slope is first smoothed to a uniform surface. Then riprap stones are hand placed to fit together like a puzzle and grouted into place to form a protective surface over the dirt slope. The adjacent eroded areas that are not under the freeway were covered with erosion control matting and planted with native grasses. This site was part of the Central Oahu Best Management Practices, Eroded Slope Repairs, Phase 2 project managed by the DOT-HWYS Salt Lake Field Office. This is just one more way DOT-HWYS continues to Protect Our Water!
This slope under the H-1 freeway in Waipahu had extreme soil erosion and poor growing conditions for establishing vegetation.
During construction, a crew hand places riprap and grouts it into place to provide permanent protection for the slope.
The completed grouted riprap surface provides permanent protection from erosion.