Mill Creek Fish Passage Improvement

This project completed designs, permitting and implementation for replacement of a fish passage barrier culvert where Ranch Creek Road (formerly Mountain Home Ranch Road) crosses Mill Creek, a tributary to Peshastin Creek. The crossing is located just off U.S. Highway 97, approximately 200 feet upstream of the Mill Creek/Peshastin Creek confluence. Mill Creek confluences with Peshastin Creek at approximately RM 5.2.

The project replaced a 4x5 concrete box culvert that was a barrier to both adult and juvenile passage. It constructed a 49ft long, open-bottom, structural plate arch culvert that is 248 wide with a 124 rise, and approximately 115 ft of step/pool streambed with an average width of approximately 15 ft. It also constructed approximately 250 ft of new asphalt road pavement and approximately 150ft of guardrail along both sides of the road where it crosses the new culvert. Following construction of the culvert, disturbed areas were seeded with a native grass/forb seed mix and mulched to minimize erosion potential. Subsequently, container grown native shrubs were planted to enhance species diversity and vertical structure within the disturbed areas (no trees were planted because of the presence of overhead powerlines). In addition to work at the culvert site, the project corrected a deficiency associated with a log weir system located approximately 600 ft upstream of the culvert. The log weirs were constructed several years earlier by another project sponsor, but scour below the lowest weir during the intervening period caused the lowest structure to become an impediment to fish passage. This project constructed an additional log/slash weir downstream of the original log weirs to aggrade the stream channel and raise water surface elevation downstream of the lowest previously-constructed log weir such that the original weir system would no long impede fish passage.

As implemented, the completed project provides for unimpeded access to approximately 2.2 miles of spawning and rearing habitat for ESA-listed steelhead trout and rearing habitat for juvenile Chinook salmon.

To improve fish passage, allowing ESA-listed anadromous fishes access to approximately 2.2 miles of spawning and rearing habitats that had been blocked by anthropogenic barriers.