Landslide Mitigation and Drainage Installation

A long-term noxious weed client suffered a large landslide in the winter of 2019, after a gutter stormwater pipe (tightline) burst at the top of their slope. This landslide was approximately 10 feet from their home foundation and required immediate attention. Large projects like this have few options: try and repair the slope or move the house further back. Our project consisted of the development of a mitigation plan – or work plan – to identify local best-available-science and prioritize needs of the slope, to determine best solutions for repair, and to formulate costs. Once the mitigation plan was developed, the client reviewed it and accepted our proposal.

Our first phase was to repair the stormwater drainage system that caused the landslide in the first place. Our team installed an above ground water conveyance system (tight line), cemented into the slope. This will stop the tight line from swaying in the wind when empty, and prevent future cracking and failure. This tight line dissipates onto the lower edge of the client’s property, over a dissipator valve and river rocks.

The second phase of the project was to build a natural, living revetment along the slope, and to reduce erosion as much as possible. This consisted of native plant installation, willow waddle installation, seeding and irrigation. Irrigation is a key component of all exposed steep slope repair projects. Without irrigation, plants would desiccate in the exposed environment; with too much irrigation, erosion will be exasperated.

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