Lorenz Gulch – Developed Alternative Dec 2012

IC‐1 STA 19+00 Large Wood Complex – large wood placement to constrict channel width, encourage scour and deposition, rack mobile wood, provide cover, and increase channel complexity by varying channel width and varying bed topography. This is a large wood structure, approximately 30 ft by 30 feet in footprint, and extending vertically from below scour depth to above the 11,000 cfs water surface. The top surface of the log jam would be planted with clump plantings of woody vegetation. Low risk to navigation because of straight, low‐velocity approach.

IC‐2 STA 21+00 – 26+00 Split flow channel complex. Purpose: increase channel complexity in low gradient, plane bed reach by altering bed and bank topography and increasing wetted edge and cover. Construction of this feature would involve fine sediment removal under footprint of structure and replacement with gravel. Large wood habitat structures incorporated into split flow channel at several locations.

IC‐3 vegetated medial bar and large wood. Between the existing channel and the constructed split channel, a vegetated bar would be constructed. Existing vegetation would be retained and augmented with clump plantings. A course bar would be constructed at the downstream end, and the entire feature would be augmented with small aggregate placements consisting of 1 to 3 stems of large wood and slash material.

STA 26+00, 28+00, 36+00 Wood Placement. Small to medium sized wood jam placements, 5‐15 main members, keyed into existing bank. Encourage localized scour, rack mobile wood, and provide cover for all life stages of fish. These would not be hydraulic structures, and would not be ballasted or secured.

R‐1 STA 28+00 – 34+00 Side Channel. Re‐activate side channel built in 1990s, but for a shorter segment. Increase wetted edge length and amount and quality of salmonid rearing habitat. Large wood incorporated into side channel at select locations. Side channel non‐navigable.

IC‐5 STA 32+00‐35+00 Skeletal Bar with Wood. Promote channel migration, pool/run consolidation. Increase velocity through existing run, enhance adult steelhead holding. Grading to lay back left bank, remove vegetation and fine sediment, and re‐create bar surface with ancillary benefits to juvenile fish, yellow legged frogs. Bar surface is proposed to have undulating topography and large wood to enhance rearing habitat area.

STA 38+00‐40+00 Riparian Berm Removal. Removal of riparian vegetation and removal of fine sediment under footprint of feature, with intention of encouraging fine gravel deposition to enhance riffle for spawning. Some benefit for juvenile rearing and yellow legged frog. Improved bank access for recreation.

STA 42+00 – 44+00 Boulder Placement. Boulder placement in existing run adjacent to exposed bedrock strath terrace on right bank. Anticipate placing 4’‐6’ diameter boulders in complexes to create pocket water and enhance adult holding, while maintaining navigability. Lower priority feature, inclusion funding dependent. Lorenz Gulch – Developed Alternative Dec 2012

42+00‐46+00 Floodplain Lowering. Floodplain lowering to target flows 2000‐6000 cfs, lower depth to groundwater to enhance riparian vegetation and create opportunities for natural recruitment. This floodplain would not have a typical “flow‐through” configuration, where flow access the floodplain from a lateral connection to the channel with flow conveyed across the floodplain in the downstream direction. Rather, this floodplain would be designed to be watered from the “bottom up”. An advantage of this configuration would be to maintain stream power within the main channel, and to capture fine sediment for enhancement of floodplain soils. This feature provides increased rearing habitat area outside the mainstem river, and has benefits for establishment of riparian vegetation.

STA 42+00 – 55+00 Side Channel Left Bank. Increase wetted edge length and amount and quality of salmonid rearing habitat. Water would predominantly enter the side channel through hyporheic flow. The mainstem Trinity overtops the left bank in this area at discharges above 6000 cfs, and would continue to do so post construction.

STA 42+00 – 50+00 Floodplain Lowering – Side Channel. Floodplain lowering adjacent to constructed side channel. Like the other floodplain lowering, this floodplain would be plumbed from the “bottom‐ up”, backwatered at discharges above 3000 cfs.

Pond – left bank side channel. This feature proposes to construct pond in‐line with side channel on the left bank. Pond grading reflects a diversity of pond depths. Increase western pond turtle and yellow legged frog habitat; provide greater diversity of fish habitat with greater temperature variation, with specific benefits for Coho salmon.

Further Analysis

Grading developed, 2D hydraulics next week (12/10‐14)

Bar Sizing: gravel/cobble matrix gradation

Right Bank Side Channel, Split Flow – dimensions and grade, adjust for flow targets

Large Wood Design

Evaluate need for infiltration gallery at left bank side channel

Boulder placement to be further evaluated at STA 33+00

Evaluate different floodplain configuration at STA 43+00 – 47+00