DESCRIPTION
Design ELJ placement and potentially improve a side channel connection on lower Grant Creek.
The lower reach of Grant Creek, a Chinook bearing tributary of the North Fork Stillaguamish, was surveyed to assess current in-stream habitat conditions relative to salmonids focusing on large woody debris, pool and riffle locations and distribution, and stream bank conditions. Geomorphological surveys were completed to assess in stream sediment inputs, budget,s and distribution and current channel morphology. Hydrological modeling was performed to analyze stream channel response to preliminary designs. The landowner, Nick Bright, was coordinated with extensively for property access, anecdotal information about high water marks and presence of salmon in the creek. Sound Salmon Solutions supported the project through facilitating coordination between A&E consultant Wild Fish Conservancy and property owner, providing input and review of 30% & 60% design drafts and preliminary design report, and administrative project management.
30% design draft was created utilizing survey results. After review the project extent was redefined and alternatives created for a one or two phase design. 30% design was finalized and 60% design draft created using further analysis of wood and sediment inputs from the upper watershed and results of hydrological modeling. 60% designs were reviewed and finalized along with preliminary design results.
The preliminary designs address the following in stream habitat deficiencies found during site surveys and analyses:
*Lack of persistent large woody debris of size and complexity to sort sediments and create and support persistent pools
*Insufficient pool formation to sustain rearing
*Disconnected off stream channels
*Diminished in stream channel complexity
*Poor floodplain connectivity
*Sparse aging deciduous dominated tree canopy deficient in conifers
Constraints defined during the survey process were:
*Adjacent land use by property owner for pasture and agroforestry
*Two vehicular bridges - one county owned, one private
*Portions of the right stream bank in the upper reaches where the bank has been armored are not owned by project landowner
*Outlet of Grant Creek to NF Stillaguamish also not owned by project landowner
Major design recommendations from the 60% designs are:
*Encourage general streambed aggradation throughout the reach
*Encourage local variations in bed slope
*Encourage side scour and widening of the channel
*Create new channel bedforms by blocking the existing thalweg and forcing an increase in
sinuosity
*Increase the pool frequency and depth of existing pools in the reach
*Slow the transport of gravel out of the reach and cause an overall decrease in the average size
of bed material
*Increase the frequency of overbank flows
*Create high flow and low summer temperature refugia for fish
The 60% design addressed these recommendations by focusing on a passive approach to improving in stream geomorphology and floodplain connectivity through strategic placement of LWD. Vertical logs installed in the stream bed, channel spanning keyed in logs, and bank anchored log clusters will be installed at specific locations to encourage changes in thalweg direction to "let the stream do the work" of sediment sorting, pool and riffle formation, side channel reconnection, and overbank flows.