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Engineers describe Loahep dam as structurally weakened; plan includes rock ramp and notch to aid fish passage
Summary
JUV Engineers told the Bellevue commission the old three-sided Loahep diversion dam lacks a foundation and has internal scouring; proposed fixes include stabilizing walls with flowable fill and rebar, cutting a low‑flow notch to move sediment, and building a rock ramp to restore fish passage.
At the May 18 meeting, RJ O'Leary of JUV Engineers described the physical condition of the Loahep diversion dam and the planned engineering response.
O'Leary said the existing structure is a three-sided wall with no formal foundation and that the interior has been scoured over time so that logs and voids now support parts of the wall. "It is a 3 sided structure...there is no actual foundation to it...the working foundation of the dam currently is some logs that are, like, propped up underneath the structure," he told the commission, citing photos taken during prior inspections.
To stabilize the dam, JUV proposes filling the structure with flowable fill and installing rebar to provide a stable foundation, rehabilitating the top slab to its likely original elevation, and constructing a rock ramp and low-flow channel to enable fish passage. O'Leary said the plan also includes cutting a notch in the dam to flush accumulated sediment through the structure and limiting any rise in floodplain elevation to the immediate project area.
O'Leary described habitat measures that include a floodplain bench, revegetation, and anchored rootwads to stabilize banks and provide cooling habitat for aquatic species. He noted coordination with Trout Unlimited for fish salvages where needed and emphasized design choices intended to preserve irrigators' ability to pass water while creating low-flow connectivity for fish.
Commissioners asked clarifying questions about locations for revegetation and the slope of the ramp; presenters offered to show plans and figures to clarify those details.
