Is a Riparian Restoration Still Viable After 100-year Storm Events Alter the Original Design? Sarah Spear Cooke, Ph.D. Seattle, Washington
Presentation Outline Introduction The site pre-restoration Restoration goals and Conceptual design Design to build riparian and buffer installation 100-year storm events 2 of them! Conditions post-storm How did the agencies feel about the changes? Have we succeeded? What have we learned?
Introduction:The site pre-restoration restoration The site: A 1,000-linear-foot stretch of Little Bear Creek, located in (barely) rural Snohomish and King Counties. The 15-foot stream is at the foot of a landfill associated with historic chemical dumps, and a junkyard. Buffers between the fill are barely 50 feet wide. Upstream is in much better shape. The floodplain is vegetated in reed canarygrass and blackberries. It is narrow (260 to 380 feet wide) and is limited by SR-522 and fill. Channel bottoms are < 5% gravels.
Riparian Conditions Were BAD Over 90 percent of the floodplain was highly degraded riparian wetland Over 80 percent cover of invasive herbaceous and woody vine species. The stream had very few habitat features for salmon.
Riparian Conditions Were BAD Almost no LWD Very few overhanging trees of shrubs Almost NO shade 90% reed canarygrass in wetland 60% blackberry in buffer
Riparian Conditions Were BAD
Restoration Goals When considering riparian/stream restorations, it is very easy to get lost in the minutiae of stream-channel characterization and bank morphology and to forget about the importance of the landscape and the vegetation lining the banks. Future LDW recruitment is essential as this project will come to show!
Restoration Goals The following riparian functions were maximized (Because up and down stream reaches were also a mess) Stream shading and thermal impacts Fine organic litter Sediment control Nutrients and other dissolved materials Large woody debris recruitment Bank stabilization Windthrow Riparian microclimate and productivity
Restoration Goals Installation of large woody debris within the creek to help reestablish pools, shade, and gravel substrates for redds Removal and continued maintenance of thorny nonnative vines and herbs a huge priority Restoration of reed canarygrass areas to diverse native trees (conifer/deciduous) and shrubs Installation of willow stakes along the creek banks to shade the stream, stabilize the stream banks, and provide fine organic litter (FOL) Installation of conifers within 50 feet of the creek centerline to provide LDW and FOL in the future
Conceptual Design-Buffer No CAD design was done for riparian or buffer areas; instead: Target habitat types were identified and acreages were identified Reference sites nearby were evaluated to determine the historic plant communities common to the area- it was very species rich historically Plant numbers were calculated with DENSE (double) spacing (to out- compete weeds, provide wiggle-room for herbivory loss, and provide future LWD)
Site Analyses Performed: Reference site selection- of a nearby pristine site to determine plant palette Hydrologic and hydraulic analyses (downstream) including: a qualitative geomorphic study for a distance of approximately one mile downstream of the site An estimate the peak discharge from a designed storm event to estimate the changes that may occur as a response to the installation of the in-stream and near-stream LWD Stream survey and basemap preparation to identify specific stream characteristics for the 1,000 feet stretch
Conceptual Design-Buffer Plant numbers were calculated with DENSE spacing (to out-compete weeds and provide future LWD) 375 trees (12 species) in addition to the 100 that were previously present 1600 shrubs (13 species) in addition to the 2500 previously present 1675 Willow stakes were planted 1 foot o.c. along both sides of creek along the 600 linear feet that had no shade
Design-Buffer From this.. To this..
Conceptual Design LWD 1:1 pool to riffle ratio Cedar or Douglas fir logs that are at least 30-inches in diameter and 25 feet long - to be installed every 30 linear feet in-creek Washington State Dept of Fish and Wildlife did not want the logs to be pinned or anchored so LDW that was max. for size and length that could be dug into the bank
Conceptual Design- In-stream No C.A.D. design was done for in-stream LWD placement, instead: No cabling or steel pinning was planned One conifer log (30 inches in diameter, 25 feet long) was placed for every 30 feet of creek
Conceptual Design- In-stream From this.. To this..
Plant Installation Problems Plant Installation Problems Soils mostly sand Irrigation difficult to access Beaver and mt beaver common Weed load huge
How do we prepare urban sites for in- stream and adjacent designs? Weed Weed Weed
LWD Installation Problems Site not accessible LWD lifted Over wall TWO 100-yr storm events occurred Within 3 months! Logs had to be hand-dug into the banks Banks consist of sand
100-year storm events- 2 of them! That shifted logs from the sensitive elbow To piles further downstream (but still on site!)
Conditions post-storm storm New logs were recruited resulting in more onsite LWD The buffer and riparian plantings had not yet occurred so none were lost and we could shift more plantings to the areas without LWD The existing reed canarygrass kept the bank stable. The flood spread reed canarygrass seed to areas that had become relatively clear and introduced new weed (knotweed!, jewelweed)
Monitoring post-storm storm new problems Weeds returned Logs shifted up bank and had to be returned to the creek
Monitoring post-storm storm new problems Beaver ate 1/3 of the willows and sitka saplings necessitating installing plastic tubing
How did the agencies feel about the LWD movement? For the most part they didn t care because: The project had done both the upstream and downstream analysis correctly No one can predict a 100-yr event (or two) The property owner had so much money invested already The site appeared stable and the dense plantings designed should, over time, further stabilize the banks and provide for on-site recruitment. FISH and FISH HABITAT had RETURNED
Should they have cared? Ideally, the wood should have stayed approximately where it was placed because: Log placement was designed to protect unstable bank features such as corners, deflection areas, and unstable sediment areas; and Areas without LWD will take longer to develop associated habitat and we see that little gravel and no redds are found in these areas.
AND we still have the following By Year 2 we have: Gravel substrate for more than 50% of the segment! Fish! Using the side pools, establishing redds (35 this year!), and rearing young.
And..excellent shade and foliage growth throughout
And, We Still Had a Site That Changed From this.. To this..
In 2 years To this..
We Still Had a Site That Changed From this.. To this in 2 years
Future Challenges We still have to deal with the elbow and 2 other places that have no LWD. We will need to watch them to be sure they are stable, and fix them if they are not Weeding is going to be ongoing for the next 3+ years We need to fix the process for establishing performance standards for instream work.
What Have We Learned? What Have We Learned? Really examine your reach analyses and know your river. Think about degree of urbanization and how the system reacts to high volume storm events. Had we done this and planned for a possible 100-yr event we would have fought the no anchoring and pinning requirement by WDFW and buried the logs further in the bank.
It s Not Enough to Plant You must plant densely to provide for future LWD and stabilize the banks
What Have We Learned? Plant densely along the banks. 1-foot o.c. is a minimum stake density - especially if there are beaver. Anchor at least some logs per each jam if you are in urban areas that experience common high volume storm events- assume they will happen. Although it is not allowed because of fish windows it would be better to install LWD in early spring so the logs have a chance to stabilize into the slope.
Willow stakes can stabilize a creek bank in just a few months, giving time for LWD to stabilize. Install them when you install LWD
What Have We Learned? And..hope you do not have a large storm event At least during the first couple of years!
Establish Performance Standards for in-stream work, for example: # of pieces of wood/stretch not tied to location Percent cover of vegetation on banks- or density of woody stems/linear foot Development of gravel % of stream bed that is gravel habitat before and after restoration, or % increase in gravel over the the restored stream reach Salmonid use # of redds before and after restoration (over time) (if you know you have salmonids in the system)
The Project Team Otak Engineers and Alan Johnson riparian design riparian and buffer planting design Stilly-Snohomish Fisheries Enhancement Task Force LWD installation Terra Dynamics planting installation and weeding
Thanks to for providing the funding for the project