South Fork Nooksack River Skagit County, Washington

Transcription

1 DRAFT Design Alternatives Investigation and Feasibility Study Elk Flats Sediment Reduction Project South Fork Nooksack River Skagit County, Washington for Lummi Nation Natural Resources Department 4

2 DRAFT Design Alternatives Investigation and Feasibility Study Elk Flats Sediment Reduction Project South Fork Nooksack River Skagit County, Washington for Lummi Nation Natural Resources Department March Dupont Street Bellingham, Washington

3 DRAFT Design Alternatives Investigation and Feasibility Study Elk Flats Sediment Reduction Project South Fork Nooksack River Skagit County, Washington March 24, 2016 Prepared for: Lummi Nation Natural Resources Department 2665 Kwina Road Bellingham, Washington Attention: Jill Komoto Prepared by: GeoEngineers, Inc. 600 Dupont Street Bellingham, Washington, Alex P. Levell Fluvial Geomorphologist Joey Smith, EIT Hydraulic Engineer Jonathan M. Ambrose Associate River Scientist APL:JMA:JS:lw Disclaimer: Any electronic form, facsimile or hard copy of the original document ( , text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.

4 Table of Contents INTRODUCTION... 1 Project Overview... 1 Project Goals and Objectives... 1 EXISTING CONDITIONS... 2 Site Location... 2 Physical Setting... 2 Channel Morphology Conditions... 3 Project Reach... 3 Slope Stability Assessment... 4 Literature Review... 4 Elk Flats Fine Sediment... 5 Climate Change and Hydrology... 5 Channel Response... 5 Hydraulic Modeling... 6 Model Elements... 6 Model Results Existing Conditions... 7 DESIGN CRITERIA... 7 Sediment Reduction... 7 Habitat Objectives... 8 Channel Response/Geomorphic Stability... 8 Constructability and Scale... 8 CONCEPTUAL DESIGN ALTERNATIVES... 9 Design Concept 1: Induced Avulsion through Large Wood Placement... 9 Design Concept 2: Partial Channel Blockage and Forced Channel Realignment... 9 Design Concept 3: Complete Channel Blockage and Forced Channel Realignment... 9 Conceptual Design Discussion and Refinement Revised Design Concept 1: Induced Avulsion through Large Wood Placement Revised Design Concept 2: Channel Blockage and Forced Channel Realignment FEASIBILITY ANALYSIS Proposed Conditions Hydraulic Modeling Revised Design Concept 1: Proposed Conditions Modeling Results Revised Design Concept 2: Proposed Conditions Modeling Results Channel Response Habitat Implications CO-MANAGER CONSULTATION March 24, 2016 Page i

5 PRELIMINARY DESIGN Meander Bend and Adjacent Left Bank Floodplain Upstream Reach and Right Bank Floodplain Downstream Reach Structure Types Apex ELJ Bank Deflection ELJs Wood Racking Structure REFERENCES LIST OF FIGURES Figure 1. Vicinity Map Figure 2. Historic Channel Traces Figure 3. Relative Water Surface Map APPENDICES Appendix A. Slope Stability Assessment Summary Memo Appendix B. Hydraulic Modeling Results Appendix C. Conceptual Design Alternative Drawings Appendix D. Feasibility Matrices Appendix E. 15% Design Plans of the Preferred Alternative Appendix F. 15% Cost Estimate Appendix G. Site Photographs March 24, 2016 Page ii

6 INTRODUCTION Project Overview The proposed Elk Flats Sediment Reduction Project is located between RM 23.1 and RM 22.6 on the South Fork Nooksack (SFN) River in Skagit County, Washington (Figure 1). The Elk Flats project site is one of several projects in various stages of planning, design, or implementation in the Nooksack River basin with the objective to protect and restore salmonid habitat. The SFN River has elevated levels of fine sediment that have detrimental effects on aquatic habitat, challenging the survival of listed salmonids within the river (Lummi 2015). Lummi Nation Natural Resources Department (LNNRD) determined that the Elk Flats project reach was contributing a large amount of fine sediment to the SFN channel through ongoing erosion of a mass wasting site called the Elk Flats slide. LNNRD identified the Elk Flats slide reach as a primary candidate for restoration and sediment reduction (Brown and Maudlin 2007) and the 2011 parcel acquisition by Whatcom Land Trust of the riparian corridor adjacent to Elk Flats initiated restoration planning by LNNRD. Through a grant provided by the Environmental Protection Agency (EPA) to the Northwest Indian Fisheries Commission, the LNNRD contracted with GeoEngineers to evaluate the slope stability of the Elk Flats slide (Appendix A), model existing and proposed hydraulic conditions (Appendix B), develop three preliminary design alternatives for co-manager review (Appendix C), complete a feasibility evaluation of alternatives to address sediment reduction at the Elk Flats site (Appendix D), and to develop 15% designs and cost estimates for a preferred (preliminary) design approach (Appendix E and F, respectively). The three preliminary design alternatives were presented at an initial design charrette attended by members of the WRIA 1 Salmon Recovery Staff Team (SRST), including representatives of the Nooksack Tribe and Whatcom Land Trust (landowner). As a result of input received at the initial design charrette, the three preliminary design alternatives were further refined to two design concepts identified for detailed feasibility evaluation. The results of the feasibility evaluation on the two refined concepts were presented at a second design charrette that included representatives of Washington Department of Fish and Wildlife (WDFW) and Whatcom County in addition to the other WRIA 1 SRST members present at the first design charrette. A result of the second charrette was the selection of a preliminary design intended to both meet the project goals and objectives and address concerns provided by co-managers. This report discusses the preliminary alternatives, the feasibility evaluation, and presents the 15% designs of the preferred approach to address sediment reduction at the Elk Flats project site. GeoEngineers services were completed in general accordance with the scope of work identified in the consultant agreement with the Lummi Indian Business Council dated October 26, Project Goals and Objectives The goal of this project is to develop a restoration approach for the Elk Flats site that is consistent with strategies presented in the Water Resource Inventory Area (WRIA) 1 Salmonid Recovery Plan (Plan). The plan s ultimate goal is to recover self-sustaining salmonid runs to harvestable levels by meeting the salmon recovery objective for early spring Chinook populations through habitat restoration that addresses limiting factors identified for the reach. Specific habitat limiting factors identified in the Elk Flats project reach include low habitat diversity, elevated fine sediment, and high water temperature. March 24, 2016 Page 1

7 The primary objectives for this project are to work within natural channel forming processes to direct the main river flow away from the Elk Flats slide, thereby reducing or eliminating hydraulic forces acting on the bank and slide toe while also increasing habitat complexity in the Upper South Fork by: Reducing fine sediment in downstream spawning gravels; Increasing available spawning gravels to downstream Chinook redds; Increasing the number of pools with woody cover; Increasing overall wood loading; Increasing side channel habitat; Improving floodplain connectivity; Reducing reach-scale incision. Previous studies found that this reach of the SFN is subject to chronic fine sediment delivery from multiple sources (WRIA , Brown and Maudlin 2007). The Elk Flats site in particular was determined to be a major fine sediment source, primarily derived from the sandy silt glaciolacustrine materials that comprise the valley walls immediately above the river (Lummi 2015). EXISTING CONDITIONS Site Location The Elk Flats Sediment Reduction Project reach extends from RM 23.1 to RM 22.6 on the South Fork Nooksack River and is located in northern Skagit County as shown on the vicinity map (Figure 1). The Elk Flats slide is situated on the river right bank on the outside of a tight meander bend immediately upstream of a steep cascade/riffle reach. The Elk Flats reach is upstream from the meander bend at a proposed Camp 18 restoration project at RM Physical Setting The SFN River is one of three forks of the Nooksack River, draining the western flanks of the Cascade Mountains in northwestern Washington State. The 184 square mile SFN watershed has a channel length of about 39 miles from its headwaters in the Twin Sisters Range to its confluence with the main stem Nooksack River near Deming (Lummi 2015). The upper 23 miles of the SFN flows through rugged peaks, hillslopes, and terraces. Mass wasting features meet the river in multiple locations, causing localized channel changes with far reaching effects. In some cases, the landslides or debris flows block the channel and force the channel to find new paths across the historic floodplain, causing lateral shifts upstream and downstream to account for changes in channel length. The watershed area above the Elk Flats reach is about 70 square miles. The bedrock geology of the upper SFN is composed of metamorphosed sedimentary and ultramafic rocks (Lummi 2015). Major rock units are the Twin Sisters Dunite, Elbow Lake Formation, the Chilliwack meta-sedimentary unit and the metamorphic Yellow Aster complex, which forms a ridge on the upper watershed (USFS 2006). March 24, 2016 Page 2

8 A series of thrust fault zones and fold belts form the Twin Sisters Range (USFS 2006, Brown and Maudlin 2007, Lummi 2015). Strike-slip and extension faulting are also common. The faulting results in springs, seeps, sag ponds and mass wasting activity. The Elbow Lake, Howard Creek area and Old Olivine Quarry site are three significant landslides, while debris avalanches and debris flows are also common in the upper SFN valley (USFS 2006). Glacial till and glaciolacustrine sediments from the Quaternary Vashon glacial stade comprise the hillslopes and valley floors throughout the upper SFN. Till caps the lacustrine deposits in some areas. The glaciolacustrine deposits were formed when glacial ice created a dam and a lake flooded the South Fork valley behind the dam, accumulating thick deposits of clay, silt and sand in the lakebed. Following glacial retreat, the ice dams eventually gave way and the river channel cut into the glaciolacustrine sediments, depositing glaciofluvial outwash material on the valley floor and flanks (USFS 2006). Modern day alluvium is deposited above glaciolacustrine and till deposits. The glaciolacustrine sediments comprising the Elk Flats valley wall are erodible due to the presence of more fine sediment than the coarser alluvium sediments on the toe and valley floor (Lummi 2015). Glaciolacustrine deposits are still found throughout the Upper SFN, regularly lining deep scour pools. The SFN river channel abrades against this deposit and works its fine sediment distribution into the modern day river channel. Channel Morphology Conditions The SFN channel has a meandering, highly sinuous planform throughout the project reach. Meander bends measured between RM 25.1 (200 Road Bridge) and RM 21.0 (Larson s Reach) display meander wavelengths between 2,000 to 4,500 feet, with amplitudes typically about 1,000 feet. Downstream of Larson s Bridge, the SFN exhibits a multi-channel planform, with forested islands and wider, broader channel bottoms. The project reach characteristics described below are derived from LNNRD reports, a desktop study, and a field reconnaissance completed on December 7, At the time of our site visit, the river flow was about 500 cubic feet per second (cfs). Photographs documenting site observations are presented in Appendix G. Project Reach The project reach extends from its upstream extent at the inlet of a side channel on the right bank at RM 23.5, downstream past the Elk Flats slide to about RM The reach begins on a gentle meander bend with plane bed morphology and a well-developed right bank side channel. The downstream end of the bend has a right bank lateral bar composed of cobbles and gravels. The right bank floodplain is a forested extension of the lateral bar while the left bank, forested floodplain is somewhat disconnected from the channel by a 4-foot high bank. Downstream of the right lateral bar, the channel slope steepens and the bed transitions to a cascade and drops into a deep pool at the bend apex at the toe of the Elk Flats slide. The geometry of this bend is typical of the Upper SFN, but it is tighter with the narrowest radius of curvature of any bend on the Upper SFN. The meander bend amplitude at the project site is a little over 700 feet, and part of a shortened wavelength of 2,100 feet. A gravel point bar inside the bend apex is prograding towards the slide, as demonstrated by growth rings and cobbles imbricated in that direction. The point bar is approximately 320 feet wide at its neck and just under 400 feet in length. Downstream of the Elk Flats pool outlet, the channel steepens again and has a rapid/riffle morphology. The channel bottom is about 80 to 90 feet wide at low flow with bankfull widths ranging from 110 to 230 feet in the project reach. Through most of the project reach, the channel is situated against the right valley wall and a wide floodplain with several short terraces extends from river left to the left valley wall. March 24, 2016 Page 3

9 The Elk Flats slide is part of the steep, high right river bank and valley wall and is situated just downstream of a forested lateral bar. There is field evidence of the channel inundating the point bar during a November 17, 2015 high flow event recorded at about 14,900 cfs at the downstream Saxon gage (USGS ), which represents between a 2 and 5 year flow event. The channel gradient is about 2 percent over the plane bed reach upstream of the Elk Flats slide, and increases to 10 percent at the cascade section immediately upstream of the pool. The channel gradient is about 2 to 3 percent immediately downstream from the pool. The gradient of the overflow channel across the point bar is 3 to 4 percent. Historically, the main channel has periodically cut across the point bar across from Elk Flats slide, similar to channel behavior observed at other meander bends upstream (Brown and Maudlin 2007) in the Upper SFN (Figure 2). GeoEngineers observed evidence of scroll marks and relict channels in the 2013 LiDAR surface analysis and relative water surface elevation analysis (Figure 3). Slope Stability Assessment GeoEngineers completed a slope stability assessment prior to developing preliminary design concepts. The purpose of the assessment was to evaluate the morphology and geologic processes active at the slide and identify potential risks associated with concepts engineered to reduce sediment delivery from the Elk Flats slide. GeoEngineers performed a desktop evaluation followed by a field visit on November 20, 2015, by a licensed engineering geologist. Based on a review of the available data and site observations, the Elk Flats Slide movement appears to be primarily driven by a loss of support via channel erosion by the SFN River. Undercutting of the bank and subsequent bank failure appears to occur episodically and the current orientation of flow will likely continue the trend of eroding bank material causing bank recession and headward progression of the landslide. The assessment concludes that moving the SFN River away from the Elk Flat Slide will reduce the potential for slope movement and sediment delivery at this location. The complete Slope Stability Assessment is presented in Appendix A. Literature Review GeoEngineers reviewed studies pertinent to the fine sediment delivery, geomorphology and habitat conditions within the Elk Flats slide project reach, including: A two-fraction model for the transport of gravel/sand mixtures (Wilcock and Kenworth 2002); WRIA-1 Salmonid Recovery Plan (WRIA ); Upper South Fork River Habitat Assessment, LNNRD report to the Salmon Recovery Funding Board (Brown and Maudlin 2007); Current and Historic Sediment Production, Storage, and Delivery to the South Fork Nooksack within the Elk Flats Sub-basin, October 2015 Environmental Protection Agency under agreement No.11EPA PSP406 to Northwest Indian Commission (Lummi 2015). Quantitative Assessment of Temperature Sensitivity of the South Fork Nooksack River Nooksack River under Future Climates using QUAL2Kw, report to Environmental Protection Agency (EPA) under agreement No.600/R-14/233 (Butcher et al. 2015). March 24, 2016 Page 4

10 Elk Flats Fine Sediment WRIA-1 (2005) and Brown and Maudlin (2007) provide historic context of and justification for fine sediment being identified as a limiting factor to habitat success. Lummi (2015) completed a sediment study of the Upper South Fork, listing the Elk Flats site as a top priority for sediment management remediation. The Lummi (2015) study considered the Elk Flats slide as a major sediment producer with detrimental impacts to downstream salmon habitat. The Lummi (2015) study found an estimated 8 million feet 3 of fine sediment load had been eroded and entered the channel from the Elk Flats site over a 68 year time period. The Lummi (2015) study also found that lateral migration may have stopped the downstream translation of the Elk Flats meander bend, consequently locking the channel into place at the Elk Flats slide. According to Lummi (2015), an estimated 18 million feet 3 of fine sediments remain composed in this slide. Fine sediment (sand) delivery to a cobbly channel bed effectively increases the mobility of all grain sizes, including gravels and cobbles (Wilcock et al. 2001; Wilcock and Kenworthy, 2002). Lummi (2015) found that sand has little to no salmon habitat value and may be contributing to downstream bed coarsening. A two part study by Wilcox (2001) and Wilcox and Kenworthy (2002) found that sand in a channel will reduce the amount of coarser sediment downstream. Bimodal distributions in sediment causes coarser clasts with sands in the interstitial spaces lubricating transport. A bimodal distribution of sand and gravel typically results in large amounts of sand and a lower amount of gravel transported (Wilcock and Kenworthy 2002). This bimodal sediment distribution in the Elk Flats project reach simplifies downstream bedform substrate while negatively affects downstream instream salmonid habitat. Climate Change and Hydrology Potential climate change impacts to the project were considered in developing hydrologic design events for hydraulic modeling. Butcher et al. (2015) completed a quantitative assessment of climate change in the South Fork Nooksack River. The Elk Flats project reach was included the study, a core salmon spawning reach with high water temperature. (Butcher et al. 2015). Climate change is expected to exacerbate legacy impacts to temperature, flow and sediment regimes in the SFN. Water temperature is expected to increase by 2.81 to 6.31 C or more by the 2080 s. Peak flow magnitudes in the South Fork are projected to increase by 4 to 39 percent, with flows in the project reach projected to increase as much as 12 percent from existing conditions. A 4 percent increase in the 2-year discharge (derived from Camp 18 hydraulic reporting) will result in an increase from 6,270 to 6,521 cfs (Table 1); a 12 percent increase will result in 7,022 cfs. A 4 percent increase in the 100-year discharge will result in flows increasing from 15,470 to 16,089 cfs (Table 1); and a 12 percent increase will result in 17,326 cfs. The Nooksack River is the second largest sediment load producer in the Puget Sound basin (Czuba et al. 2011) and we anticipate that increased peak flows will both accelerate sediment mobility processes and hydraulic contact with the Elk Flats slide. Channel Response A direct relationship exists between a river s system-wide channel width, length, and mean radius of curvature and all three naturally adjust to changes in any one characteristic. For example, a change in the radius of curvature at a meander bend caused by bank erosion and bend migration result in changes to channel width and length, or channel length changes caused by a meander bend cutoff cause adjustments to nearby meander bend radius and channel width (Leopold 1994, Knighton 1998). Nanson and Hickon (1986) found that migration rates are greatest when the ratio of radii of curvatures to channel March 24, 2016 Page 5

11 widths is between 2 and 3 and that channels will naturally adjust to tight radius of curvature by cutting off at necks or chutes (Knighton 1994). Chute cutoffs are the most common as they occur across low gradient bars created by prior channel occupancy. Meander cutoffs alleviate energy exerted on the outside of the bend, but the bends upstream and downstream from these avulsions will respond by widening. The overall effect from chute cutoffs is to increase channel gradients and the localized sediment transport ability (Knighton 1994). Hydraulic Modeling GeoEngineers developed a cursory two-dimensional, steady-state hydraulic model for the Elk Flats project reach utilizing Hydronia s RiverFlow2D software. The goal of the hydraulic modeling was to gain a better understanding of the hydraulic forces and level of floodplain inundation at the site under existing conditions and compare to modeled results for two separate proposed design conditions. RiverFlow2D utilizes a flexible triangular mesh to characterize the river bathymetry and surrounding floodplain surfaces and allow for determination of flow direction and velocities in both the main channel direction (downstream and upstream) and perpendicular to main channel flow (overbank and floodplain flows). This allows for a detailed level of hydraulic output related to both overbank flows across the Elk Flats floodplain area and in channel flows. Model Elements The existing conditions hydraulic model was built using LiDAR topographic data collected in 2013 and supplemented with pool depth data collected by LNNRD staff in fall Pool depths were collected from the approximate head of the pool adjacent the Elk Flats slide downstream approximately 300 feet to the pool tail out. The pool depths were used to generate a triangular irregular network (TIN) surface of the pool bathymetry and that surface was burned in to the LiDAR surface in order to better represent the hydraulic conditions caused by the deep pool in the modeling results. The two-dimensional model includes a river reach of approximately 1.5 miles in length, extending 0.75 miles both upstream and downstream from the location of the Elk Flats slide. Mesh spacing was generally 5-feet within the bankfull channel of the South Fork Nooksack and ranged from 2 to 25 feet in the floodplain areas. Floodplain mesh spacing was smaller in areas of interest such as the right bank side channel upstream from the Elk Flats slide and locations of relict channels in the Elk Flats left floodplain. RiverFlow 2D utilizes Manning s N values to account for the roughness effects on flow hydraulics in the channel and floodplain areas. Manning s N values were assigned to the channel and floodplain areas based on observations made about channel substrate, bank composition, and floodplain conditions during the site visit and standard hydraulic references. TABLE AND 100-YEAR DESIGN DISCHARGE VOLUMES ADJUSTED FOR PREDICTED CLIMATE CHANGE. Flow Event 2-Year 6, Year 16,089 Discharge (cfs) March 24, 2016 Page 6

12 Model Results Existing Conditions Results from the existing conditions modeling efforts were used to characterize existing conditions at the project location, inform the development of preliminary design alternatives, and serve as the baseline for comparing proposed conditions of the two selected conceptual design concepts. Model output showing depth and velocities throughout the project reach are presented in Appendix B. During the 2-year event, modeling predicts that flow is almost completely contained within the active channel. There is evidence of flow through the right bank side channels upstream of the Elk Flats slide and a small amount of inundation over the left bank point bar near the apex of the rightward meander bed. The inundation modeled along the left bank matches up with evidence of overbank flows that were observed during our site visit following the 2 to 5 year flood event that occurred November 17, Velocities modeled throughout the channel are relatively high at between 10 and 17 feet per second (fps), likely due to the flow confinement and lack of floodplain activation. Velocities predicted in the model may be overestimated considering the lack of actual bathymetry for all areas other than the pool. The model results for the 100-year flow event predict inundation over the entire left bank of the Elk Flats floodplain as well as the right bank floodplain and side channels. Modeled flow paths in the left bank floodplain show that the majority of overbank flow is routed through a large beaver pond complex (observed during December 2015 site visit) and re-enters the SF Nooksack at an existing outlet from the beaver pond complex, located approximately 1,500 feet downstream of the Elk Flats slide. Flow depths in the left floodplain area ranged from 0.5 to 3 feet. Modeled main channel velocities during the 100-year flow are higher than those modeled for the 2-year event, with velocities in the fps range. DESIGN CRITERIA Design criteria were identified to use in development and evaluation of each design concept with respect to meeting project goals and objectives. We used screening criteria to evaluate design elements with respect to meeting the primary and secondary project objectives. Sediment reduction was the primary objective, while habitat improvements were secondary. Scale of project impacts and constructability were other screening factors for the design criteria. The following summarizes the initial, screening level design criteria: Sediment Reduction The primary design objective is to reduce fine sediment input to the South Fork Nooksack from the Elk Flats slide. Based on an evaluation of the hydraulic data, field data, and geomorphic assessment, the preferred approach to reduce the sediment delivery is to move the channel away from this source rather than attempt to protect/armor the bank from hydraulic forces. Therefore, the design approach considered multiple means to shift a large portion of the river flow into the left bank floodplain. This shift is expected to produce multiple effects that will reduce sediment contributions to the river. Moving the main channel away from the landslide will eliminate sediment delivered by ongoing plucking and raveling of the lowcohesion river bank. During high flow events, shifting flow onto the floodplain will reduce the hydraulic forces at the toe of the slide that entrain and mobilize sediment and oversteepen the lower bank, causing ongoing slumping of large volumes of material from the upper slope. Engaging the floodplain at a wider range of flow events will also reduce the duration of time the landslide is exposed to flow and able to contribute sediment to the river. March 24, 2016 Page 7

13 Habitat Objectives GeoEngineers reviewed the WRIA-1 Recovery Plan (WRIA ) and the Upper South Fork River Habitat Assessment (Brown and Maudlin 2007) for habitat limiting factors in the project reach. As part of the design criteria for the Elk Flats concepts, the following limiting factors were considered: Increase channel complexity through activation of existing side channels, development of new side channels, and incorporation of large woody debris; Installation of ELJ structures to develop scour pools with complex habitat and cover for salmonids; Encourage development of multiple deep pools with woody cover, throughout project reach. Channel Response/Geomorphic Stability GeoEngineers considered how the project reach will adjust to shortening and steepening of the channel through the cutoff channel/forced avulsion. Hydraulic modeling for existing conditions showing the 2-year flow is contained within the main channel indicates that the river is incised and entrenched at the slide location. Continued bank erosion at the slide is decreasing the meander bend radius as the bend tightens. We expect the eventual channel response will be a meander bend cutoff or avulsion across the left floodplain, as observed elsewhere in the upper SFN. Upstream and downstream meander bends would adjust to a natural channel avulsion with channel widening, sediment deposition, and development of new meander bends or migration/expansion of existing bends. Channel response to the proposed concepts was assessed by reviewing modeled predictions of velocity and shear stress throughout the project reach and comparing to the predicted channel response for a natural avulsion. Any changes in channel planform, gradient, cross sectional geometry and floodplain interaction at the project reach were evaluated for channel response at upstream and downstream reaches. Constructability and Scale GeoEngineers reviewed how to most effectively design a project that meets project objectives, while considering the scale of such efforts. The cost of wood, amount of water diversions, and other factors of scale were considered for how they would influence the regulatory restrictions, funding and other obstacles required to successfully complete this project. To mitigate wood costs, LNNRD considered utilizing onsite trees into the project design. Whatcom Land Trust, the Elk Flats parcel owner, and Sierra Pacific Industries, which owns adjacent parcels, must be regularly consulted for construction and post construction monitoring access. Regular consultations with project co-managers is required to address concerns about the project s scale. Three designs were developed for consideration and review following the initial criteria screening. These alternatives were evaluated for their performance in achieving sediment reduction, meeting project habitat objectives, predicted channel response, and constructability. Two design alternatives were then advanced to a detailed feasibility analysis using specific project-level design criteria which are discussed in the feasibility analysis section below and presented in Appendix D. March 24, 2016 Page 8

14 CONCEPTUAL DESIGN ALTERNATIVES GeoEngineers developed three preliminary design concepts for review. These conceptual alternatives were developed based on the information gained during the background review and hydraulic modeling and are intended to address the project goals and design criteria described above. The conceptual alternatives represent a range of options for accomplishing the project objectives with varying project scope, approach, anticipated cost, and long term changes to the project site. Conceptual alternatives were presented to the LNNRD, Whatcom Land Trust, and members of the WRIA 1 Salmon Recovery Staff Team during the first design charrette on December 18, Concept design alternative drawings are presented in Appendix C and their major elements are summarized below. Design Concept 1: Induced Avulsion through Large Wood Placement Design Concept No. 1 involves installing multiple engineered log jam (ELJ) structures and a single, channel spanning wood racking structure to encourage floodplain inundation on the left bank with the long term goal of encouraging a channel avulsion through the floodplain. The wood racking structure will accumulate mobile wood in the system and encourage aggradation upstream of the structure, thereby increasing the likelihood of floodplain engagement. Targeted bank grading in coordination with flow redirection ELJs placed in the main channel will create favorable locations for the floodplain to be activated and will ideally lead to the development of a channel avulsion and additional side channels. This alternative would likely require more time than the more aggressive design to achieve the stated project objectives, but would not require large scale excavation and channel grading on the floodplain. Design Concept 2: Partial Channel Blockage and Forced Channel Realignment Design Concept No. 2 involves re-routing the main stem of the river across the left bank floodplain by grading out a new main channel alignment. A wood racking structure will be installed across the existing channel to block the majority of flows from entering the pool adjacent to the slide and instead route these flows into the newly formed channel. A side channel will be created on the left bank floodplain upstream from the location of new channel alignment. At the downstream end of the reach, a wood racking structure will be installed to promote aggradation and reduce the ongoing channel incision in the reach. Flow redirection and apex style ELJ structures will be installed to help encourage the desired channel planform and provide multiple fish habitat benefits. This concept represents a more aggressive approach at forcing the channel to a new alignment and will result in immediate reduction of sediment delivery into the river. The wood racking structure will be designed to allow flood flows to overtop the structure, helping to minimize the size and cost of this alternative. The proposed left bank side channel will be excavated and graded for approximately ⅓ of its length and the remainder of the channel allowed to develop naturally as it is exposed to higher flow events. Design Concept 3: Complete Channel Blockage and Forced Channel Realignment Design Concept No.3 represents the most aggressive approach at meeting project objectives. It involves grading a new channel alignment similar to Concept 2; however it employs a much larger structure to obstruct the existing channel, resulting in less frequent activation of the existing channel adjacent to the slide. The alignment of the proposed channel is made into a more gradual bend in this approach which increases the overall volumes of channel grading. A wood racking structure will be installed at the March 24, 2016 Page 9

15 downstream end of the reach similar to Concept 2 to limit incision. A new left bank side channel will be excavated and graded out across the left bank floodplain to its outlet upstream from the wood racking structure. Additional flow direction and apex ELJs will be installed to help shift flows toward the left floodplain and protect the unstable right bank downstream from the proposed channel alignment. Conceptual Design Discussion and Refinement The three designs above were presented at Design Charrette No.1, and were then revised based on input to develop two designs for more detailed hydraulic modeling and feasibility analysis. The two revised design alternatives were modeled using RiverFlow2D and compared to the results of the existing conditions modeling to evaluate design feasibility and predict channel response. An additional goal of the hydraulic modeling was to test the effect of certain design elements on a desired project outcome between the two proposed designs (e.g., include right bank ELJs at the upstream end of the existing side channels to increase activation). To facilitate the selection of a preferred alternative to bring to a 15% design level, the two revised preliminary designs were evaluated with respect to their engineering feasibility, anticipated channel responses, and effect on instream habitat. The design concepts for which the modeling and feasibility analysis were completed are presented below. Conceptual drawings of the two refined design concepts are presented in Appendix C and discussed below: Revised Design Concept 1: Induced Avulsion through Large Wood Placement Revised Design Concept No.1 is similar in scope to Design Concept No.1 described above and represents a less intensive, longer term approach to reducing sediment input in the reach. Key design components of Revised Design Concept No.1 are listed below: Wood racking structure partially obstructs flow away from the slide and encourages avulsion over point bar; Targeted grading to create a narrow pilot channel for the induced avulsion pathway; Targeted grading to encourage greater floodplain inundation at high flow events to reduce hydraulic forces at toe of slide. Install ELJs downstream of the new channel outlet stabilize the channel planform and protect existing right bank/valley slope. No proposed actions for the existing right bank side channel. The existing right bank side channel discharges downstream of the cutoff to provide some flow into the pool and improve water quality and habitat. Revised Design Concept 2: Channel Blockage and Forced Channel Realignment Revised Design Concept No.2 represents a combination of Design Concepts No. s 2 and 3 described above and aims to re-route the existing main channel by obstructing the flow path that directs the channel toward the toe of the slide and redirecting away from the slide, resulting in an immediate reduction in sediment input. Key components of Revised Design Concept No.2 are described below: A large woody debris plug in the existing channel and excavated new main stem channel forces the channel planform across point bar; March 24, 2016 Page 10

16 The wood plug composition mimics the coarse material of a debris slide toe deposit. Over time, the pool may fill with debris off the bank and sediment from upstream transported via the right bank side channel. The new channel planform will resemble a nearby upstream reference reach of the upper South Fork Flood flows above 10-year event will overtop the large woody debris plug; A wood reinforced riffle installed downstream promotes aggradation and reduces reach-scale incision; A new side channel will be graded across the left bank floodplain upstream from the proposed channel alignment. Construction of the side channel will incorporate small scale wood habitat features; and Existing right bank side channel will be enhanced using ELJs at the head to increase the periodicity of side channel activation. FEASIBILITY ANALYSIS The feasibility analysis involved comparing the two revised design concepts for their perceived effectiveness at meeting the design criteria. The results of the feasibility analysis were presented at Design Charrette No.2 for comment and review by members of the WRIA 1 Salmon Recovery Staff Team. The feasibility analysis included a three tiered evaluation which included a review of the engineering, geomorphic, and habitat development feasibility of the two revised design concepts. The engineering feasibility ranked topics for constructability (e.g., access and staging, equipment requirements, water management, etc.), cost (e.g., log costs), effectiveness, and project risk. Geomorphic feasibility evaluated and ranked how channel response to each concept at multiple locations within and downstream of the project reach. The habitat matrix ranked how the habitat limiting factors described in the Upper South Fork Habitat Assessment (Brown and Maudlin 2007) are addressed by each of the two revised design concepts. Proposed Conditions Hydraulic Modeling To more quantitatively assess how the two revised design concepts meet project objectives and their effect on the hydraulic conditions within the reach, GeoEngineers developed a proposed condition RiverFlow 2D model for each of the revised design concepts. The modeling approach utilized the existing conditions model described above with modifications to the model mesh geometry and roughness values in order to replicate the as-built conditions of each design. Areas with proposed grading were altered to match the anticipated as-built conditions of the project. ELJ and wood structures were modeled by raising the model surface to the design height of the structures within the footprint of the structures. For the wood racking structures, model geometry was raised slightly and roughness values were increased substantially to account for the added flow resistance from these structures. The same 2-year and 100-year discharges applied to the existing conditions model were used for the proposed conditions. Model results are discussed below: Revised Design Concept 1: Proposed Conditions Modeling Results Model results for Revised Design Concept No.1 show that this design approach results in a significant increase in inundation throughout the left bank floodplain. Model results were evaluated at the 2-year March 24, 2016 Page 11

17 flow event rather than the 100-year event, as the 2-year flow event represents the channel forming flow that will have a significant effect on altering conditions within the reach. 2-year flow depths throughout the floodplain range from 1 4 feet versus no inundation in the existing conditions model. The installation of the wood racking structure and grading of the pilot channel across the point bar results in a small increase in flow depth (up to 2 feet) at the toe of the slide, but a significant reduction in flow velocities, decreasing by 2 4 fps compared to existing conditions. This increase in water surface elevation at the toe of the slide is caused by the overtopping of the wood racking structure, which was designed to be overtopped at the approximate 2 year flow. This results in an increase the water surface elevation immediately upstream of the slide which increases pool depths and water surface elevations in the pool. It is important to note that this increase is water surface elevation at the toe of the slide would only occur during flow events which overtop the wood racking structure and for the majority of flow events, the water surface elevations in the pool will be decreased. Based on a step-wise modeling approach where discrete design elements were modeled individually, it appears that the upstream ELJs and targeted bank excavation areas are the driving force for the large increase in floodplain inundation. This suggests that this approach is a cost effective way at increasing floodplain inundation at the 2-year flow event. Modeling of the pilot channel predicts velocities in the range of fps throughout the pilot channel. Based on these results, we would expect the pilot channel to effectively transport the adjacent floodplain sediments, resulting in the growth of the channel until it reached a stable width and alignment. The downstream ELJs lining both banks at the end of the project reach are effective at reducing velocities along the bank and thereby protecting the banks, but result in an increase of velocities throughout the center of the channel which could increase the incision already present in the reach. The existing right bank side channels upstream of the slide see a minimal increase in flow depths compared to the existing conditions. Flow depths increase by up to 1 foot in at the 2-year flow and are likely due to the increase in water surface elevation caused by the placement of the ELJ structures in the upstream portion of the reach. Revised Design Concept 2: Proposed Conditions Modeling Results Results from the proposed conditions modeling of Revised Design Concept No.2 show a much larger effect on the hydraulic forces at the toe of the slide and a similar increase in inundation along the left bank floodplain. 2-year flow depths at the toe of the slide increase by up to 1 foot, and velocities are slowed by 4 6 fps compared to existing 2 year conditions. Flow depths along the toe of the slide are slightly increased due to the overtopping of the wood structure as described in Revised Design Concept 1 above. Similarity, flows under the 2-year event which do not overtop the wood racking structure would result in decreased flow depths and water surface elevations at the toe of the slide. Flow depths in the excavated channel are between 4-6 feet with velocities ranging from fps. This installation of ELJ structures along the right bank of the proposed channel appear to be effective at redirecting flow into the channel and maintaining channel alignment. With these rather high velocities, a stable channel design and additional roughness elements may be required to ensure the channel alignment and profile are stable. March 24, 2016 Page 12

18 Floodplain inundation is similar as under revised design concept No.1, but depths are reduced especially in the existing beaver complex area. This is likely due to the excavation of the side channel which effectively routes overbank flows away from the beaver complex toward the center of the floodplain area. For this design concept the side channel was graded approximately ⅓ of the distance across the floodplain and then allowed to find its own route back to the main stem channel. Results of the velocity vector directions and flow visualization indicate that once water leaves the graded side channel it flows northwesterly until it is captured by relict channel scars located to the south of the main stem channel. These relict channels capture the floodplain flow and redirect it to the west where it meets up with the existing outlet channel from the beaver complex area and eventually outlets back to the main stem. The wood racking structure at the downstream of the project reach is effective at slowing velocities in the downstream portion of the reach with a reduction of velocities between 2 8 fps compared to existing conditions. We would expect this type of structure to be more effective than the ELJs proposed in Revised Concept No.1 at reducing incision and promoting aggradation in this portion of the reach. Channel Response To meet design objectives to move the channel away from the Elk Flats slide, the channel length is reduced up to 800 feet (Appendix E). Geomorphically, this adjustment of channel length will influence the SFN upstream and downstream. Based on the relationships between meander bend radius of curvature, wavelengths, and channel widths, meander bends will adjust upstream and downstream first by widening to account for a loss of channel length. Bank and floodplain resistance to erosion will determine the location of channel widening and project mitigation measures may include additional structures to encourage widening within the project reach, downstream of the Elk Flats slide where the stream is incised. Without proper mitigation, channel response may be translated further downstream, creating temporary channel instability in unplanned or undesirable areas. The channel may attempt to steepen through its new path across the point bar. The initial cut across the point bar will cause elevation differences between the inlet and outlet of the channel cutoff. Model output indicated that the outlet of the channel cutoff has increased velocities from existing conditions at the 2-year discharge, which threatens knickpoint propagation. Some headcutting upstream into the main channel may beneficially mobilize coarse sediment to augment incised areas downstream and result in habitat uplift. This gradient steepening and high velocity may be managed by adding additional structure across the new cutoff channel to mitigate headcutting. Upstream sediment mobilization and downstream eddying and aggradation will also maintain channel stability. Habitat Implications The survival rate of salmonids in the upper South Fork are influenced by the habitat quality in their reach with respect to the life stage, such as fine sediment negatively affecting the egg incubation and emergence life cycles (WRIA ). The Elk Flats slide will deliver substantially less fine sediment to the SFN, which will lower downstream delivery to juvenile egg incubation in spawning redds (Appendix D). The Elk Flats slide is the closest fine sediment delivery source to the spawning grounds in the Larson s and Fobes reaches, both critical for juvenile life stage development (Brown and Maudlin 2007, Lummi 2015). Local habitat diversity will be improved with deep scour pools associated with woody cover, long-term mid channel island development and side channel connectivity. High temperatures will be lowered through hyporheic interactions within the added pools, as well as increasing engagement to the cool water spring source on the right bank. March 24, 2016 Page 13

19 CO-MANAGER CONSULTATION LNNRD held two design charrettes attended by the landowner and WRIA 1 SRST members to determine the most effective restoration solutions to the Elk Flats slide. Meeting attendees included representatives from the Whatcom Land Trust (WLT), Washington Department of Fish and Wildlife (WDFW), the Nooksack Indian Tribe and Whatcom County Public Works. The first charrette was set up to select two alternatives for a feasibility review. The purposed of the second charrette was to discuss the feasibility review of the two revised design concepts developed as an outcome of the first design charrette, and the selection of a preliminary design concept to move forward to a 15% design and cost estimate (Appendix F). PRELIMINARY DESIGN Following Design Charrette No.2, GeoEngineers developed a preliminary design alternative to meet project objectives based on feedback from meeting attendees and co-managers regarding project goals, costs and logistics. The preliminary design concept contained elements of the previously discussed design concepts and built upon the insight gained during the hydraulic modeling and feasibility analysis of the two revised design concepts. Preliminary design drawings are located in Appendix E and discussed below. Discussion of the preliminary design focuses on three specific locations of the project site, the meander bend located at the toe of the slide and associated left bank floodplain, upstream reach and right bank floodplain and downstream reach. Meander Bend and Adjacent Left Bank Floodplain The proposed 15% design aims to re-route the main stem of the SFN through the left bank floodplain in a manner that emulates a cutoff avulsion across the meander bend. A new channel will be graded in this location and is designed to convey flows up to between a year flow event. The proposed channel will require grading of existing sediments and backfilling with a coarse cobble-gravel sediment mixture designed to match existing sediment distribution in the reach. A wood racking structure will be placed in the proposed channel location to aid in maintaining grade and sediment stability in the proposed channel, while allowing for the racking of instream wood to promote sediment aggradation. The sides of the proposed channel will be lined with wood and boulder roughness elements to help maintain the channel planform, reduce near bank velocities, and increase aquatic edge habitat. The existing path of the SFN will be obstructed by a wood racking structure that is angled to shift flows into the proposed channel path. This structure will be located upstream of the pool at the base of the slide and will extend across the riffle and onto the right bank floodplain to prevent flanking. In addition to shifting flows, this structure will also reduce flows into the pool located at the toe of the slide, thereby decreasing the hydraulic forces causing sediment entrainment and ongoing toe failures. The structure is also designed to rack instream wood. Racking instream wood will increase its effectiveness at blocking the existing channel alignment over time. Two apex ELJ structures are proposed to be incorporated into the wood racking structure on either side of the current low flow channel. These structures are designed to deflect flows toward the proposed channel and reduce the hydraulic forces applied directly to the wood racking structure, thereby increasing stability and reducing scale of the wood racking structure. March 24, 2016 Page 14

20 Over time, we anticipate the SFN channel will remain in its new alignment and instream wood will rack on the wood racking structure, increasing aggradation upstream of the structures. These changes will reduce the frequency of high energy flow events abrading against the toe of the Elk Flats slide and decrease sediment input from the slide. In the long term it is possible that the existing pool at the toe of the slide will fill in as the slide stabilizes and reaches a more gradual slope. Upstream Reach and Right Bank Floodplain In the upstream reach of the project, we propose installing four apex ELJs to deflect flows onto the overbank floodplains and increase water surface elevations. One ELJ will be placed at the head of the most frequently activated side channel on the right bank floodplain to increase the range of flows that activate this side channel. On the left bank a pair of ELJs will be placed to function in concert with targeted grading of the left bank to increase overbank flows onto the left bank floodplain. This will result in more effectively spreading out flows during high flow events, reducing in channel velocities and shear stresses, and reversing historical incision. Overtime, the placement of the ELJs and targeted grading may lead to the development of a side channel through the left bank floodplain, which would likely be routed into the existing stream that discharges from the beaver complex area and rejoins the main stem near the downstream end of the project reach. Downstream Reach In the downstream end of the project reach, bank based ELJs are proposed to protect the existing right bank downstream of the slide and to help maintain the alignment of the proposed channel. These structures will extend out from the banks to redirect flows back toward the center of the channel. Additionally these structures will likely develop scour pools extending from their tips and will improve habitat in the downstream portion of the reach. The structures located on the right bank downstream of the slide will also interact with an existing cool-water spring that will provide valuable cool water refugia habitat during the low flow summer months. Structure Types We propose three wood structure types to accomplish the project objectives and design intent described above. Typical details for these structure types can be found in Appendix E. Apex ELJ Apex ELJs are designed to be placed within the active channel in order to locally elevate water surface elevations, split flows and develop scour pools along their margins. These structures are currently designed to extend above the 100-year water surface elevation and remain actively engaged during all flows. The structures will likely be pile supported and ballasted with material excavated during structure construction. Excess substrate from structure excavation and construction will be placed on the tail of the structure to create a mid-channel island which will be planted with riparian vegetation. Apex ELJs will also be used to redirect flows in a favorable direction, such as into existing side channels or the proposed main stem channel location. Additional apex ELJs provide high quality, complex aquatic habitat consisting of deep pools and woody cover. Current habitat conditions within the reach show mainly riffle-glide complexes with the exception of the large, deep pool at the toe of the slide. This pool however, has somewhat limited habitat value due to its lack of cover and relatively high velocities. The March 24, 2016 Page 15

21 addition of apex ELJ structures in the reach will improve both habitat quality and quantity. Apex structures are proposed both in the meander bend and upstream reach portions of the project as described above. Bank Deflection ELJs Bank deflection ELJs are designed to be placed along the right bank in the downstream portion of the reach to protect the existing bank and redirect flows into the center of the channel. These structures are triangular shaped with their base along the channel banks and tip extending into the channel. Bank deflection structures will be embedded into existing banks and ballasted with native substrate for structure stability. The proposed realignment of the main stem will result in an altered flow path through the reach and could potentially increase hydraulic forces on the right bank downstream of the existing slide location. The proposed bank deflection ELJs will be placed in areas anticipated to see increased hydraulic forces, thereby protecting the existing bank and realigning the flow in the downstream portion of the project. In addition to protecting the banks, these structures will improve edge habitat and will form scour pools extending from their tips into the center of the channel. Wood Racking Structure The wood racking structure is designed to extend across the channel and collect mobile instream wood in the system. The design intent of the wood racking structure is to decrease velocities and encourage aggradation upstream of the structure helping to stabilize the channel grade. The wood racking structure across the existing main stem is angled across the channel to redirect flows toward the proposed channel as well as block flows into the existing channel alignment at the toe of the slide. These structures will be pile supported and primarily consist of horizontal members with root wads oriented upstream to collect mobile wood. The wood racking structure is designed to be overtopped during large flow events, but will effectively redirect flows from the existing channel into the proposed channel during lower flows, including channel forming discharges (such as the 2-year flow event). The wood racking structure placed in the proposed channel functions to eliminate the delivery of fine sediment over time from the Elk Flats slide, maintain the proposed channel plan and profile, and decrease velocities as flows transition to the new channel and downstream reach. REFERENCES Brown, M. and Maudlin, M Upper South Fork Nooksack River Habitat Assessment. Salmon Recovery Funding Board under agreement IAC No N. Butcher, J., Faizullabhoy, M., Nicholas, H., Cada, P. and Kennedy, J Quantitative Assessment of Temperature Sensitivity of the South Fork Nooksack River Nooksack River under Future Climates using QUAL2Kw. Environmental Protection Agency under agreement No.600/R-14/233. Czuba, J.A., C.S. Magirl, C.R. Czuba, E.E. Grossman, C.A. Curran, A.S. Gendaszek, and R.S. Dinicola Sediment Load from Major Rivers into Puget Sound and its Adjacent Waters. USGS Fact Sheet U.S. Geological Survey. Knighton, D Fluvial Forms and Processes: A New Perspective. Arnold. Leopold, L A View of the River. Harvard University Press. March 24, 2016 Page 16

22 Lummi Nation Natural Resources Department (LNNRD) Current and Historic Sediment Production, Storage, and Delivery to the South Fork Nooksack within the Elk Flats Sub-basin. Environmental Protection Agency under agreement No.11EPA PSP406 to Northwest Indian Commission. Nanson, G. and Hickin, E A statistical analysis of bank erosion and channel migration in western Canada: Geological Society of America Bulletin, 97, United States Forest Service (USFS) Middle Fork and South Fork Nooksack Rivers Watershed Analysis. Water Resources Inventory Area (WRIA)-1 SRFB (Salmon Recovery Funding Board) Water Resources Inventory Area (WRIA)-1 Salmonid Recovery Plan. Submitted to Shared Strategy for Puget Sound October pp.Wilcock, P Toward a practical method for estimating sediment transport rates in gravel-bed rivers. Earth Surface Processes and Landforms Wilcock, P. and Kenworthy, S A two-fraction model for the transport of sand/gravel mixtures. Water Resources Research 38, March 24, 2016 Page 17

23 FIGURES

24 FOBES REACH LARSON'S REACH PROJECT SITE 200 ROAD BRIDGE Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community, Copyright: 2013 National Geographic Society P:\1\ \GIS\MXD\ _F1.mxd Lyman Copyright: 2013 National Geographic Society Notes: 1. The locations of all features shown are approximate. 2. This drawing is for information purposes. It is intended to assist in showing features discussed in an attached document. GeoEngineers, Inc. can not guarantee the accuracy and content of electronic files. The master file is stored by GeoEngineers, Inc. and will serve as the official record of this communication. 3. It is unlawful to copy or reproduce all or any part thereof, whether for personal use or resale, without permission. Data Sources: ESRI ArcGIS Online Transverse Mercator, Zone 10 N North, North American Datum 1983 North arrow oriented to grid north µ 2, ,000 Feet Vicinity Map South Fork Nooksack River Elk Flats Sediment Reduction Project Skagit County Washington Figure 1