Yamaguchi South River Improvement Project Public Comment Responses

Rock Cross Vane: This structure is built with large angular rocks place to converge water towards the middle of the river. The objectives of the structures are to: provide cover and holding water for fish, cause a redirection of shear stress away from the bank towards the center of the river, sustain a pool form on the downstream side of the structure, provide vertical grade control, increase the width/depth ratio, improve sediment transport capacity, and provide a natural sorting of gravel on the tail out of the downstream pool. The structure is usually symmetrical in shape and ties into the ordinary high-water elevation on each side of the river.

Rock Habitat Clusters: The rock habitat cluster is a series of several rocks clustered together usually located near the center of the river channel. The objectives of these clusters are to: provide in stream holding areas for fish, to create local scour and flow diversity in the middle of the channel. These structure are typically built by placing 4-5 large rocks (50 square feet) in clusters in the existing river channel.

Rock and Wood Deflectors: The rock and wood deflectors are a series stacked rocks and/or placed is in such a way to turn water off the outside of a bank and converge the water on the downstream face of the structure causing a deep scour pool to form. The objectives of the structures are to: provide increased bank stability in high shear stress locations, maintain a wide navigation lane in the center of the river, create cover and holding water for fish, and to create excellent spawning gravels in the downstream eddy below the structure. The structure is usually tied to and elevation equal to or above ordinary high water on one side of the river.

Native Material Revetment/Root Wads: The root wad structure are typically used in combination with a large rock structure to ensure the wood material remains stable during high water events. The objectives of these structures are to: provide shade and cover, detritus, terrestrial insect habitat, enhance the natural look of the river, and provide complexity to the subsurface fish habitat. These structures consist of 5-10 large (1’-3’ diameter) cottonwood root balls with approximately 10’-20’ of trunk that are partially buried in the riverbank and extend out into the river channel with the root ball to provide the desired habitat.

Short Vane: The structure is similar to the rock cross vane except it ties to only one side of the river - typically on the outside of a river bend. The objectives of the structures are to: create and sustain cover and holding water for fish, protect the bank from erosion, and create wide long pools that provide spawning habitat for fish. The structure is asymmetrical in shape and ties into the ordinary high-water elevation on one side of the river.

Irrigation Wet Well: Structure used in irrigation systems to collect and store water, typically from groundwater or surface water sources, for later distribution to agricultural fields or landscapes.

Irrigation Diversion Structure: A hydraulic structure designed to redirect water from the river into an irrigation system for landscape use. These structures control the amount and direction of water flow, ensuring that water is efficiently diverted for irrigation without causing harm to the natural water system.

Irrigation Channel: A watercourse designed to transport water from the river to the existing wetland/pond and future irrigation wet well for irrigation purposes.

Wetland area/Pond improvements: An existing pond area will be enhanced with intense riparian and wetland species planting. A strong riparian vegetation community means better cover for terrestrial species that use the river for water and for its riparian forage potential. Dense riparian vegetation encourages deposition of fine-grained sediment for soil building, and also creates backwater areas that are the genesis of obligate wetland communities. Mature riparian vegetation stands, where existing, will remain intact during and after construction. This vegetation is important for streambank stability, terrestrial habitat and visual/aesthetic screening.

Boat Ramp/River Access: Access to the river will be improved through individual pedestrian trails down to the river bank as well as a new gravel boat ramp that will be available for commercial and private river users. The new river features will be accessed utilizing a new access road, trail system, parking area, and boat ramp.