Assessment of Summer Temperatures and Feasibility and Design of Improved Adult Chinook Salmon Thermal Refuge Habitat in the Sammamish River

Prepared for: Muckleshoot Indian Tribe Fisheries Division Auburn WA

Prepared by: R2 Resource Consultants 15250 NE 95th St 1998 Photo by Roger Tabor, USFWS Adult Chinook Holding in Pool Near Marymoor Park Redmond WA 98052

December 30, 2010

Assessment of Summer Temperatures and Feasibility and Design of Improved Adult Chinook Salmon Thermal Refuge Habitat in the Sammamish River

Prepared for: Holly Coccoli, Project Manager Muckleshoot Indian Tribe Fisheries Division Auburn WA

Prepared by: Paul DeVries PhD, PE Clair Yoder PE Chiming Huang PhD, PE Glen Anderson PE Karee Oliver Mike Cooksey

R2 Resource Consultants Inc. 15250 NE 95th St Redmond WA 98052

December 30, 2010 Muckleshoot Indian Tribe Fisheries Division Sammamish River Thermal Refuge Habitat

CONTENTS

EXECUTIVE SUMMARY ...... XIII 1. INTRODUCTION ...... 1

1.1 OVERVIEW OF FLOW AND TEMPERATURE CONDITIONS AFFECTING ADULT CHINOOK SALMON IN THE SAMMAMISH RIVER ...... 3 1.1.1 Review of Flow and Temperature Gage Data ...... 3 1.1.2 Synopsis of Other Relevant Water Quality Studies ...... 14 1.2 OVERVIEW OF THIS STUDY AND REPORT OUTLINE ...... 18 2. TEMPERATURE ASSESSMENT METHODS...... 21

2.1 TEMPERATURE MEASUREMENT ...... 22 2.1.1 Calibration ...... 23 2.1.2 Grab Samples/Temperature Profiles ...... 24 2.1.3 Continuous Temperature Loggers ...... 25 2.2 LONGITUDINAL PROFILE SAMPLING ...... 26

2.3 DETAILED SAMPLE SITE SELECTION ...... 29

2.4 FLOW MEASUREMENT ...... 31

2.5 DETAILED SITE TEMPERATURE FIELD DATA COLLECTION ...... 32 2.5.1 Field Data Collection ...... 32 2.5.2 Analysis ...... 35 3. RESULTS OF FIELD ASSESSMENTS ...... 38

3.1 LONGITUDINAL PROFILE ...... 40

3.2 SAMPLE SITE SELECTION...... 43

3.3 DETAILED SITE TEMPERATURE FIELDS ...... 43 3.3.1 Tributary Sites ...... 46 3.3.2 Winery Pool Site ...... 47 4. RANKING/PRIORITIZATION OF SITES FOR HABITAT IMPROVEMENT PROJECTS ...... 55

4.1 SWAMP CREEK ...... 55

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4.2 HORSE CREEK (TRIBUTARY 0068) ...... 56

4.3 NORTH CREEK ...... 56

4.4 LITTLE BEAR CREEK ...... 57

4.5 GOLD CREEK (TRIBUTARY 0088) ...... 58

4.6 WINERY POOL AT TOLT PIPELINE ...... 59

4.7 DERBY CREEK AND TRIBUTARY 0090 ...... 60

4.8 TRIBUTARY 0091...... 60

4.9 OUTLET OF CONSTRUCTED WETLANDS AT NE 124TH ST/HOLLYWOOD PUMP STATION .....61

4.10 TRIBUTARY 0101...... 62

4.11 TRIBUTARY 0102...... 62

4.12 PETERS CREEK (TRIBUTARY 0104) ...... 62

4.13 BEAR CREEK ...... 63

4.14 TRIBUTARY 0142...... 65

4.15 THE FIVE HIGHEST PRIORITY SITES WITH GREATEST POTENTIAL TO BENEFIT CHINOOK SALMON HABITAT THROUGH INCREASED THERMAL REFUGE HABITAT VOLUME ...... 66 5. POSSIBLE STRUCTURAL MEASURES FOR IMPROVING THERMAL REFUGE HABITAT IN THE SAMMAMISH RIVER ...... 71

5.1 CONCEPTUAL DESIGNS FOR THE FIVE HIGHEST PRIORITY SITES ...... 71 5.1.1 Gold Creek ...... 74 5.1.2 Bear Creek ...... 75 5.1.3 Tributary 0091 ...... 76 5.1.4 North Creek ...... 77 5.1.5 Little Bear Creek ...... 79 5.1.6 Permitting Requirements ...... 79 5.2 FINAL DESIGN FOR THE GOLD CREEK SITE ...... 80 5.2.1 2-Dimensional (2-D) Modeling of Flow and Temperature ...... 80 5.2.2 Design Overview ...... 85 5.2.3 Assessment of 100-yr Flood Zero-Rise Criterion ...... 87

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6. POTENTIAL BENEFITS OF INCREASING TRIBUTARY SUMMER FLOWS TO IMPROVE THERMAL REFUGE HABITAT IN THE SAMMAMISH RIVER ...... 90

6.1 THEORETICAL ANALYSIS ...... 90

6.2 FIELD DATA ASSESSMENT ...... 92

6.3 2-D MODELING AT GOLD CREEK SITE ...... 95 7. DISCUSSIONS AND CONCLUSIONS ...... 99

7.1 DISCUSSION ...... 99

7.2 CONCLUSIONS AND RECOMMENDATIONS ...... 103 8. REFERENCES ...... 106

APPENDIX A: Detailed Sample Site Maps APPENDIX B: Temperature Profile Data Collected in July/August 2010 APPENDIX C: Representative Contour Maps of Water Temperature Fields for Different Depths at Sampled Sites in the Sammamish River APPENDIX D: Conceptual Design Drawings at 5 Sites APPENDIX E: CAD Design Drawings, Gold Creek Site

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FIGURES

Figure 1-1. Project Area (source: DeGasperi 2005a)...... 2 Figure 1-2. Locations of continuous stream flow and temperature gages with data describing the summer flow and temperature regime of the Sammamish River and its largest tributaries...... 6 Figure 1-3. Sammamish River (Station 51T) monthly flow duration curves for July through October...... 7 Figure 1-4. Bear Creek (Station 02a) monthly flow duration curves for July through October...... 8 Figure 1-5. Little Bear Creek (Station 30a) monthly flow duration curves for July through October...... 8 Figure 1-6. North Creek (Station Nr) monthly flow duration curves for July through October...... 9 Figure 1-7. Swamp Creek (Station SI) monthly flow duration curves for July through October ...... 9 Figure 1-8. Sammamish River (Station 51T) monthly maximum daily temperature duration curves for July through October...... 11 Figure 1-9. Bear Creek (Station 02a) monthly maximum daily temperature duration curves for July through October...... 11 Figure 1-10. Little Bear Creek (Station 30a) monthly maximum daily temperature duration curves for July through October...... 12 Figure 1-11. North Creek (Station 45a) monthly maximum daily temperature duration curves for July through October...... 12 Figure 1-12. Swamp Creek (Station SI) monthly maximum daily temperature duration curves for July through October...... 13

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Figure 1-13. Predicted changes in surface area between consecutive isothermal contour lines for depth-averaged water temperatures in the Sammamish River (108 cfs) after constructing the proposed alternative. Simulated upstream water temperatures were 20ºC and 22ºC for the Sammamish River (i.e., two model runs), and 17.3ºC consistently for North Creek (18 cfs). Each histogram bar represents the post- minus pre-project difference in area bounded between isothermal contour lines for the labeled temperature (Ti) and the next lower temperature (Ti-1 = Ti-0.5°C). The negative bars for the 20°C and 21.5°C contours reflect areas of the stream that become cooler with the project (i.e., = „lost‟ area; Figure copied from R2 2009b)...... 19 Figure 2-1. Example daily variation in water temperature in the Sammamish River and North Creek, and general time period in which longitudinal and detailed site temperature profile sampling of water temperatures occurred, indicated by the arrows...... 22 Figure 2-2. Comparison of temperature calibration results for the pre-field work test conducted on July 7, 2010...... 24 Figure 2-3. Comparison of temperature calibration results for the pre-field work test conducted on October 5, 2010...... 26 Figure 2-4. Location of detailed temperature measurement sites within the Sammamish River basin...... 34 Figure 3-1. Observed water temperatures in the Sammamish River for April through September 2010...... 38 Figure 3-2. Observed temperature in the Sammamish River at R2‟s continuous monitoring sites (top), and comparison with the King County gage at Station 51T located near NE 116th St...... 39 Figure 3-3. Longitudinal profile measurements made July 26-29, 2010 of surface and near-bottom water temperatures, and corresponding depth at measurement location, in the Sammamish River. Tributaries are identified by name/WDFW stream catalog number (Williams et al. 1975) and temperature during the survey. Note that depressed temperatures at tributary locations reflect measurements nearer the mouth, not necessarily river thalweg...... 41 Figure 4-1. Bedload deposit along right bank of Sammamish River at the Little Bear Creek confluence. Photo was taken standing in Little Bear Creek...... 58

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Figure 4-2. Bridge pilings under NE 145th Street bridge. Tributary 0091 enters at the left edge of the photograph. Photo was taken December 2010 demonstrating influence of pilings on flow...... 61 Figure 4-3. Confluence of the Sammamish River and Bear Creek. Note the convex portion of left bank that may deflect higher flows partially towards the right bank below the mouth during high flow, as suggested by the left arrow. The larger flood flows in Bear Creek and the confluence geometry also appear to work against excessive deposition at the mouth (as seen for example at the confluence with Little Bear Creek; Figure 4-2)...... 65 Figure 4-4. Mean increases in (i) mean daily and (ii) maximum daily water temperatures between King County gages located in Bear Creek at Union Hill Road and the mouth, for the months of July and August over the period of record. Missing data indicate incomplete record...... 66 Figure 5-1. Conceptual representation of three-dimensional flow patterns occurring in the confluence zone during the summer low flow period, as suggested by vertical temperature profile data. Warmer Sammamish River water flows over a descending cooler plume from North Creek, resulting in the warmer water measurements recorded along the right bank (from R2 2009a)...... 78 Figure 5-2. 2-D hydrodynamic model domain and bathymetry of the Gold Creek design site. Flow in the Sammamish River is to the top of the page; Gold Creek enters from the right bank...... 82 Figure 5-3. 2-D hydrodynamic model temperature field predictions simulating without (top) and with (bottom) the proposed structure design detailed in Appendix E for the Gold Creek site; QSammamish=57cfs, QGoldCreek=2.9cfs, o o TSammamish=20.7 C, TGoldCreek=15.4 C, WSE at downstream boundary of Sammamish River is 996.16ft, based on local datum...... 84 Figure 5-4. HEC-RAS cross-section at River Station 37100.64 with a 10 ft wide by 2 ft high flow obstruction added to simulate the effects of the proposed structure on the flow field. The 100-year flood water surface elevation is depicted. Predicted mean channel velocity = 2.65 ft/s...... 88 Figure 6-1. Example calculation of temperature contours for a simplified representation of the Sammamish River with a tributary point source located at the axes origin. The area enclosed within the 18°C contour is illustrated by light shading. River flow (60 cfs) is left to right, tributary flow = 15% of river, mainstem/tributary temperatures = 20°C/14°C...... 92

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Figure 6-2. Surface response curve of predicted available habitat area as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence...... 93 Figure 6-3. Surface response curve generated for measured available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. The irregular peaks in the mid-range of flows reflect the scatter of data from North, Little Bear, and Gold creeks (cf. Table 3-3)...... 94 Figure 6-4. Surface response curves of regression model predictions of available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. Top: model including flow-temperature interaction term; Bottom: model excluding interaction term...... 96 Figure 6-5. Regression model predictions of available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. Top: model including flow-temperature interaction term; Bottom: model excluding interaction term...... 97 Figure 6-6. Surface response curve for the Gold Creek site of available habitat area predicted by the 2-D hydrodynamic-temperature model as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence...... 98 Figure 7-1. Range of observed temperature differences and flow percentages in the Sammamish River and tributaries for which detailed temperature data were collected at tributary confluences in July and August 2010...... 103

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TABLES

Table 1-1. List of available flow and temperature data for the Sammamish River and tributaries...... 4 Table 1-2. Average monthly (July through October) streamflow for the Sammamish River and tributaries...... 7 Table 1-3. Monthly mean (column 1), mean of the monthly maximum (column 2), and maximum (column 3) temperature measured at King County and Snohomish County water quality monitoring stations in the Sammamish River and tributaries in July-October for the period of record at each station...... 10 Table 2-1. Field measurements and data quality indicators used on this project...... 22 Table 2-2. Difference in reference thermometer and temperature instrument measurements for the first calibration test on July 7, 2010...... 25 Table 2-3. Difference in reference thermometer and temperature instrument measurements for the second calibration test on October 5, 2010...... 27 Table 2-4. Summary of Sammamish River longitudinal profile survey dates and conditions...... 28 Table 2-5. Candidate Sammamish River tributaries for synoptic temperature-flow sampling based on the WDFW Puget Sound stream catalog (Williams et al. 1975) and other information...... 30 Table 3-1. Summary of temperature drops observed during the longitudinal profile data collection ...... 42 Table 3-2. Review of Sammamish River tributaries identified, their thermal influence, and recommendations for detailed temperature field sampling based on the results of the longitudinal temperature profile sampling and miscellaneous grab samples...... 44 Table 3-3. Summary of site flow and temperature characteristics sampled for detailed temperature profile data in the Sammamish River, summer 2010 ...... 48 Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft...... 50

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EXECUTIVE SUMMARY

This project was conceived to assess thermal refuge habitat availability and to identify and develop measures for increasing such habitat in the Sammamish River for adult migrant Chinook salmon (Oncorhynchus tshawytscha) during the warm summer and fall months when water temperatures can frequently exceed water quality criteria. Summer water temperatures were measured during July and August, 2010. While the year proved to be relatively cool overall with few warm spells resulting in river temperatures exceeding 23°C, the data collected could still be used to meet project objectives.

A longitudinal profile was first measured of surface and bottom water temperatures along the length of the river between Lake Sammamish and Lake Washington. The measurements focused on identifying cooling locations at the confluences of tributaries and in pools that could potentially be used by holding adult salmon. Reaches upstream of the weir at Marymoor Park and downstream of Wayne Golf Course in Bothell were found to be under the thermal stratification influences of lakes Sammamish and Washington, respectively. Seven tributaries were identified as having greatest cooling influence, including, from upstream to downstream: Tributary 0142 (per stream catalog numbering system, Williams et al. 1975), Bear Creek, Tributary 0091, Gold Creek, Little Bear Creek, North Creek, and Swamp Creek. These sites were selected for more detailed measurements of temperature fields and bathymetry to quantify the volume of water cooler than specified temperatures. Three smaller tributary sites were also selected for sampling to increase the range of stream sizes and mixing field volumes analyzed; the streams included: Tributary 0090, Derby Creek (no number), and Horse Creek (Tributary 0068).

No pools were found with significant vertical temperature stratification upstream of North Creek. Nonetheless, a pool located in the vicinity of the Tolt River pipeline crossing that was observed in 1998 to hold fish was also selected for detailed measurements to further investigate the apparent lack of significant vertical thermal stratification. Minor stratification was observed downstream of North Creek within the confined section of the river that appeared to be variously under the influence of both groundwater springs and Lake Washington.

Elevation and temperature profile data were collected over an irregular spatial grid at each detailed site to quantify cool water habitat volumes. Data were collected between 2-7 pm generally, during the warmest portion of the day. The grid extended until all temperatures in the profile exceeded 19-20°C so that the extent of data collection covered the entire portion of the

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mixing field with more suitable temperatures for adult Chinook salmon. Isothermal contour lines were developed using a gridding and plotting software package, corresponding to increasing increments of +1°C above the influent tributary temperature. The volume contained within isothermal contours was subsequently calculated. The volumes contained within different temperature increase contours were then analyzed with flows measured in the tributary and either measured or estimated for the Sammamish River upstream of the tributary.

The detailed site data indicated strongest cooling influences at Bear Creek, North Creek, Little Bear Creek, and Gold Creek. Results were confounded at the mouth of Swamp Creek reflecting the thermal influence of Lake Washington and warming that occurs in the creek backwater extending upstream from the mouth. Minor influence was measured at Tributaries 0142, 0091, and Horse Creek. There was a negligible influence measured at the other tributary sites. Only a 0.2°C difference was measured between bottom and surface temperatures at the pool site.

Two types of measures were evaluated for thermal enhancement at tributary confluences: construction of physical structures to retard mixing and extend the cool water plume, and flow augmentation of tributaries. Each candidate site was evaluated for attributes conducive to or constraining feasibility and benefits of structural measures, and for potential to expand the cool water plume. A ranking system was developed specific to this project that was used to rank and prioritize sites for further consideration and development of conceptual designs. The system led to the following ranking of sites for structural enhancement measures, from highest to lowest priority: Gold Creek, Bear Creek, Tributary 0091, North Creek, and Little Bear Creek. Up to three types of conceptual designs were developed for each site, including (1) an instream structure to separate the tributary inflow from the main river flow, (2) reconstructing the river to a meandering planform where a bend scour pool would be created and maintained at a tributary confluence, and (3) a combination of the first two.

Of the five sites, Gold Creek was selected as most feasible at this time for enhancing thermal refuge habitat for adult Chinook salmon migrants using structural measures. The Bear Creek site had the greatest potential area of thermal mixing zone expansion, but was not selected because of City of Redmond plans to relocate lower Bear Creek and move the mouth downstream approximately 100 ft, and warmer than expected temperatures that appear to reflect warming in the lower reach of the tributary. Given the importance of this tributary confluence to adult Chinook salmon, it is recommended that the final creek relocation design include consideration of potential effects on thermal refuge habitat quantity under the new confluence configuration. Planned riparian restoration along lower Bear Creek may help reduce stream temperatures in the future. The Tributary 0091 site was identified because it had a relatively large cooling influence

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for a small tributary and an enhanced mixing zone would extend under a bridge that provides shade cover, but was not selected at this time because of potential infrastructure-related complications. However, the Tributary 0091 site would be a highly suitable project concurrent with any future bridge repair or replacement work. The North Creek site, which had also been evaluated previously by R2 in a study for the City of Bothell, provided substantive cooling habitat, but was not selected for final design as part of this project because of potential complications related to impacts to recreation and other factors. The Little Bear Creek site was not selected because additional analysis would be required to address a heavy gravel bedload depositing out of the creek at the mouth without impacting spawning habitat used by sockeye salmon (O. nerka), and relatively heavy recreation use of the stream at this location.

An instream log structure was designed to retard mixing and increase the thermal plume footprint at the Gold Creek site. The structure was designed to be simple with minimal earthwork required. A depth-averaged 2-dimensional (2-D) hydrodynamic temperature model (RMA2, RMA4) was developed for the site and used to evaluate the increase in cool water refuge habitat created. The analysis indicated that the area of river with temperatures less than 19°C could be expanded by approximately 930 ft2 with the proposed design, from a baseline of approximately 1030 ft2 without logs. To achieve roughly an equivalent increase in area through flow augmentation would require more than doubling the summer low flow in Gold Creek (i.e., >2 cfs) to a level that is approximately 10 percent of the flow upstream in the Sammamish River.

The design to expand thermal refuge habitat at the Gold Creek confluence may be considered as final, ready for permitting, with the caveat that it does not include consideration of potential geotechnical design needs, private and public property constraints, flood control management needs, and unanticipated permitting requirements that may arise. In addition, the design could potentially be optimized further to maximize thermal influence while balancing construction costs and permitting constraints. A no-rise analysis using a recently completed Flood Insurance Study HEC-RAS model indicates the structure does not result in a more than 0.01 ft predicted change in stage at the 100-year flood (i.e., modeling error) without requiring significant bank excavation.

As an alternative to structural measures, three types of analyses were performed to evaluate the potential benefits of augmenting summer flows in tributaries on cool water refuge habitat in the river: (1) a simplified 2-D theoretical spreadsheet analysis was performed using basic mixing theory and representing a tributary as a point source; (2) the empirical temperature contour volume and flow data collected in July and August were evaluated using surface response curves and multiple regression analysis; and (3) using the 2-D hydrodynamic temperature model

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developed for the Gold Creek site to evaluate selected increases in summer flow in Gold Creek. It should be noted that this study makes no conclusions regarding the feasibility of augmenting flows and only evaluates how much augmentation could potentially be required to have a beneficial effect.

The analysis indicated that some additional benefit could be achieved through flow augmentation when the tributary inflow accounts for less than about 5% of the river inflow to the confluence, and when the temperature difference between tributary and river is around 3°C or more. Greatest increases in thermal refuge habitat availability due to flow augmentation are likely to be realized when the tributary inflow accounts for more than about 8%-10% of the river inflow, which is the case for Bear Creek and North Creek. Increases in habitat availability are less when tributary inflows are between about 5%-10% of the river inflow, but still appear to be sufficient to make flow augmentation a potentially realistic habitat enhancement tool for the Sammamish River. Comparison of the empirical data with modeling results suggests that within this flow range, an increase in thermal refuge habitat volume with tributary flow may be more substantive than an increase in area.

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1. INTRODUCTION

The Sammamish River is an important salmon migration corridor within the Lake Washington basin (WRIA 8; Figure 1-1) and serves as the ecological link between the watersheds of Lake Sammamish and Lake Washington, with annual average salmon runs totaling in the tens of thousands. The nearly 14 mile long river has a low gradient and a median summer low flow of about 60 cfs at the King County gage 51T located near River Mile (RM) 9. Its channel has been deepened, confined, and shortened compared to its predevelopment state (U.S. Army Corps of Engineers and King County 2002). Riparian shade conditions are generally poor. Most of the river‟s historic, extensive floodplain wetlands have been drained, and restoration opportunities are constrained by utility and flood control infrastructure and urban and agricultural land use.

Elevated water temperatures in the river during the July-September period have been identified as a significant factor limiting production of Chinook salmon (Oncorhynchus tshawytscha) and other anadromous salmonid species during their spawning migration to Issaquah Creek, the Washington Department of Fish and Wildlife (WDFW) Issaquah Creek Hatchery, Bear Creek, and other tributaries downstream (WRIA 8 Steering Committee 2005). Daily maximum temperatures frequently exceed 20°C near the Lake Sammamish outlet during this period and have exceeded 26.6°C (King County data). A major driver for elevated temperatures is that the river draws its water from the surface layer of Lake Sammamish, which gets very warm during summer months. The resulting elevated water temperatures are potentially connected with observed pre-spawn mortality that occurs in the system (DeGasperi 2001; Tabor 2002). The elevated temperatures also adversely affect the fitness of adult Chinook salmon and may delay their arrival at spawning grounds. Analyses of tracking data collected collaboratively by Washington Department of Fish and Wildlife (WDFW), the Muckleshoot Indian Tribe Fisheries Division (MITFD), the U.S. Fish and Wildlife Service (USFWS), and King County indicate that adult Chinook wait to enter the Sammamish River until water temperatures become more tolerable, or alternatively enter the river beginning in mid to late August and hold in localized cooler pockets associated with groundwater and at the confluences of cooler tributaries (Fresh et al. 1999). Water temperatures during this period can be within the range of those causing adverse physiological and behavioral effects. Ultrasonically-tracked Chinook salmon were found to spend an average of 9 days in the Sammamish River in 1998 and showed a preference for pools with a maximum residence time in a single pool of 24 days. Temperatures during that period were often near lethal levels (Fresh et al. 1999).

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Figure 1-1. Project Area (source: DeGasperi 2005a).

It has been hypothesized during the development of the WRIA 8 Chinook Salmon Conservation Plan (WRIA 8 Steering Committee 2005) and Sammamish River Corridor Action Plan (USACE and King County 2002) that providing additional cool water refuge habitat in the mainstem Sammamish River would benefit adult and juvenile anadromous salmonids. There are two types of cool water habitat documented in the river: tributary confluences and pools. The largest

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tributaries are, in general order from largest to smallest: Bear Creek (also referred to as Big Bear Creek; drainage area = 48.4 mi2), North Creek (28.5 mi2), Swamp Creek (22.8 mi2), and Little Bear Creek (15.6 mi2). Water temperatures in each of these streams are cooler than in the Sammamish River during the July-September period. The cooler water in the mixing zone at each confluence provides a thermal refuge zone that upstream migrants can utilize to rest, and potentially hold until thermal conditions in the river become less stressful. Other, smaller tributaries may also provide cool water refuge habitat to varying extents. It has been proposed in the plan that, in appropriate cases, expanding confluence mixing zones with cooler water temperatures may result in increased holding habitat availability for adult Chinook salmon that move upstream from Lake Washington.

Pool habitat not associated with tributary confluences is sparse along the length of the river, which resembles more of a regime canal with a uniform, prismatic channel. Pool spacing typically exceeds 1 mile, and most pools are not well defined. In work performed by the MITFD, only two pools were found to meet Timber Fish and Wildlife (TFW) criteria for depth and cover to be classified as a pool. Fresh et al. (1999) found Chinook salmon to use “pool” areas that in the majority of locations were only marginally deeper than the adjacent channel and/or were small in area. Temperatures up to 2°C cooler than the river surface were found at the bottom of some pools. Fresh et al. (1999) concluded that adult Chinook salmon would benefit from more pool habitat in general, and especially in the reach between Bear Creek and Lake Sammamish.

1.1 OVERVIEW OF FLOW AND TEMPERATURE CONDITIONS AFFECTING ADULT CHINOOK SALMON IN THE SAMMAMISH RIVER This section provides an overview of available, relevant flow and temperature data and studies that were used to guide development and refinement of the study plan and methods.

1.1.1 Review of Flow and Temperature Gage Data A summary of all temperature and flow gage data available for the Sammamish River and its tributaries is provided in Table 1-1. These gage data were reviewed to help understand the hydrologic and temperature regime of the system. The main gages evaluated for flow and temperature trends are shown in Figure 1-2.

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Table 1-1. List of available flow and temperature data for the Sammamish River and tributaries. Identification Type of Data Frequency Period of Location Code Available of Data Record Agency Monthly Sammamish River King 0486 Temperature grab 1971-present upstream of Bear Creek County samples Sammamish River at Grab King 0450cc Temperature 2009-present 145th St samples County Monthly Sammamish River at King 0450 Temperature grab 1971-2008 Kenmore County samples Sammamish River at 2001- King 51m Streamflow Continuous Marymoor Weir Present County 51T Sammamish River at Streamflow/ King Continuous 2005-present the 116th St NE Bridge (former USGS Temperature County 12125000) Sammamish River below the weir at the King 51P Temperature Continuous 2000-present Marymoor Park County entrance Sammamish River at King upper Redmond 51L Temperature Continuous 2001-present County railroad bridge support Sammamish River at King 51N Temperature Continuous 1995-2008 Powerlines County Sammamish River King 51R Temperature Continuous 2001-2010 below Little Bear Creek County 0484 Grab 1971-present King Bear Creek Temperature samples County Bear Creek at the King 02j Temperature Continuous 1995-2008 Mouth County Bear Creek at Union Streamflow/ King 02a Continuous 1987-present Hill Road Temperature County Monthly King Little Bear Creek 0478 Temperature grab 1971-present County samples Little Bear Creek at Streamflow/ King 30a Continuous 1998-2007 SR202 Temperature County

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Table 1-1. List of available flow and temperature data for the Sammamish River and tributaries. Identification Type of Data Frequency Period of Location Code Available of Data Record Agency Little Bear Creek at Streamflow/ Snohomish LBLD Continuous 2000-present 228th St SE Temperature County Monthly North Creek at the King 0474 Temperature grab 1976-present mouth County samples North Creek north of King 45a Temperature Continuous 2000-2008 HWY 522 County Streamflow/ Snohomish North Creek at 196th St Nr Continuous 2001-present Temperature County Monthly Swamp Creek at the King 0470 Temperature grab 1972-present mouth County samples Swamp Creek near Streamflow/ Snohomish SI Continuous 2001-present 228th Temperature County

1.1.1.1 Flow Data Average low-flow monthly flows for the Sammamish River and its tributaries are summarized in Table 1-2. Flow duration curves for the Sammamish River and four of the main tributaries for the months of July through October are provided in Figures 1-3 through 1-7. Note that the period of records are provided in Table 1-1 and are different depending on the station. Flow in the Sammamish River during this low flow period ranges between 50 and 250 cfs with the lowest flows occurring in the months of August and September. The largest tributary to the Sammamish River is Bear Creek which has a summer low flow ranging from 10 cfs to 100 cfs with an average around 25 cfs. The other three tributaries, Little Bear Creek, North Creek, and Swamp Creek contribute a much smaller portion of the flow in the Sammamish River. Flow in these three tributaries is similar and contribute an average of between 6 and 15 cfs depending on the month.

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Gage Nr North Creek at 196th Street

Gage SI Swamp Creek near 228th Street

Gage 30a Little Bear Creek at State Route 202

Gage 45a North Creek at Highway 522

Gage 51T Sammamish River at 116th Street Lake Washington Gage 02a Bear Creek at Union Hill Road

Gage 51m Sammamish River 1.75 1.75 at Marymoor Weir Lake Miles Sammamish

Figure 1-2. Locations of continuous stream flow and temperature gages with data describing the summer flow and temperature regime of the Sammamish River and its largest tributaries.

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Table 1-2. Average monthly (July through October) streamflow for the Sammamish River and tributaries. Location July August September October Sammamish River 51m 63.2 35.4 38.1 60.3 Sammamish River 51T 102.0 61.0 66.6 104.9 Bear Creek 02a 26.0 21.4 24.1 40.3 Little Bear Creek 30a 9.3 8.2 8.6 15.3 North Creek Nr 6.5 6.6 9.1 15.8 Swamp Creek SI 6.9 7.0 8.6 17.8

Station 51T - Sammamish River

250 Jul Aug Sep Oct 200

150

100 Streamflow (cfs)Streamflow

0 20 40 60 80 100 Percent Exceedance Figure 1-3. Sammamish River (Station 51T) monthly flow duration curves for July through October.

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Station 02a - Bear Creek at Union Hill Rd

150 Jul Aug Sep Oct

100

Streamflow (cfs)Streamflow 50

0 20 40 60 80 100 Percent Exceedance Figure 1-4. Bear Creek (Station 02a) monthly flow duration curves for July through October.

Station 30a - Little Bear Creek at SR202

100 Jul Aug Sep 80 Oct

40 Streamflow (cfs)Streamflow

0 20 40 60 80 100 Percent Exceedance Figure 1-5. Little Bear Creek (Station 30a) monthly flow duration curves for July through October.

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Station Nr - North Creek at 196th St

100 Jul Aug Sep 80 Oct

40 Streamflow (cfs)Streamflow

0 20 40 60 80 100 Percent Exceedance Figure 1-6. North Creek (Station Nr) monthly flow duration curves for July through October.

Station SI - Swamp Creek near 228th St

100 Jul Aug Sep 80 Oct

40 Streamflow (cfs)Streamflow

0 20 40 60 80 100 Percent Exceedance Figure 1-7. Swamp Creek (Station SI) monthly flow duration curves for July through October

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1.1.1.2 Temperature Data Continuous temperature data are available in the Sammamish River and several of its tributaries. Monthly summary statistics for July through October are provided in Table 1-3. The Sammamish River is on average 3°C to 5°C warmer than its tributaries during the summer months. The difference in temperature is more pronounced during the hours with peak temperatures and can be more than 6°C different based on comparison of mean of the monthly maximum values. Swamp Creek is on average the coolest tributary, but Little Bear Creek has a cooler maximum temperature. Duration curves by month of the maximum daily temperature are provided in Figures 1-8 through 1-12. Even though Bear Creek has the highest temperature of all of the tributaries, it has the highest potential to influence the mainstem temperature since the streamflow is three to four times larger than the others.

Table 1-3. Monthly mean (column 1), mean of the monthly maximum (column 2), and maximum (column 3) temperature measured at King County and Snohomish County water quality monitoring stations in the Sammamish River and tributaries in July-October for the period of record at each station. Station Name, No. July August September October Column (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) (2) (3) Sammamish 20.8 24.6 27.3 19.9 23.6 26.1 16.9 19.8 20.7 13.0 15.6 17.5 River 51T Bear Creek 17.3 21.8 24.7 16.8 20.1 22.9 14.2 17.8 21.8 10.6 14.2 20.1 02a Little Bear 15.6 18.4 19.7 15.5 18.0 18.6 13.4 16.1 16.8 10.6 13.0 15.4 Creek 30a North Creek 16.9 21.2 22.5 16.4 19.8 20.7 14.0 17.7 19.4 11.0 14.0 15.9 45a Swamp 15.2 19.3 21.2 14.9 18.2 19.6 13.0 16.0 16.8 10.1 13.2 15.4 Creek SI

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Station 51T - Sammamish River

10 Jul Aug Sep Oct Temperature(degrees Celcius) 5

0 20 40 60 80 100 Percent Exceedance Figure 1-8. Sammamish River (Station 51T) monthly maximum daily temperature duration curves for July through October.

Station 02a - Bear Creek at Union Hill

10 Jul Aug Sep Oct

Temperature(degrees Celcius) 5

0 20 40 60 80 100 Percent Exceedance Figure 1-9. Bear Creek (Station 02a) monthly maximum daily temperature duration curves for July through October.

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Station 30a - Little Bear Creek at SR202

Jul Aug Sep Oct

5 Temperature(degrees Celcius)

0 20 40 60 80 100 Percent Exceedance Figure 1-10. Little Bear Creek (Station 30a) monthly maximum daily temperature duration curves for July through October.

Station 45a - North Creek near 522

Jul Aug Sep Oct

Temperature(degrees Celcius) 5

0 20 40 60 80 100 Percent Exceedance Figure 1-11. North Creek (Station 45a) monthly maximum daily temperature duration curves for July through October.

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Station SI - Swamp Creek near 228th

Jul Aug Sep Oct

5 Temperature(degrees Celcius)

0 20 40 60 80 100 Percent Exceedance Figure 1-12. Swamp Creek (Station SI) monthly maximum daily temperature duration curves for July through October.

1.1.1.3 Exceedances of Adult Chinook Salmon Migration and Holding Temperature Criteria As noted by DeGasperi (2009,) the Washington State Department of Ecology (DOE) has determined that river beneficial uses for aquatic life are impaired and require establishment of Total Maximum Daily Loads (TMDLs) to remedy high summer temperatures per Section 303(d) of the Clean Water Act. Washington State Water Quality Standards for temperature are applied based on aquatic life uses. The applicable aquatic life use category for the Sammamish River is the Salmonid Rearing and Migration Only Category which has a standard of 17.5°C 7-DADMax (DOE 2006). The Sammamish River regularly exceeds this criterion. Data from station 51T exceeded the standard in the months of July through October every year temperature gage data were available.

In a review of temperature criteria and available literature, DOE concluded that to prevent a risk of causing blockage of migrating Chinook salmon, daily maximum temperatures should not exceed 21-22°C (Hicks 2002). This range is generally consistent with levels of migration blockage reported in the review by Richter and Kolmes (2005). As shown in Figure 1-8, a maximum daily temperature of 21°C was exceeded 73% of the time in July and 42% of the time

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in August for the period of record available (2005-2010). This study also concluded that in order to protect adult fish that are holding throughout the summer, the average water temperatures should be maintained below 13-14°C and the 7-day average of the daily maximum temperatures (7-DADM) maintained below 16-17°C. Tagging studies performed from 1998-2000 found adult Chinook migrating between late July and early November, with significant variation between years (Fresh et al. 1999; E. Warner, MITFD personal communication) and. Review of historical data at Station 51T shows that the 7-DADM exceeded a temperature of 16°C 85 percent of the time in September and 9 percent of the time in October. Therefore, implementation of measures to increase thermal refuge habitat can have biologically meaningful benefits to migrating adult Chinook salmon.

1.1.2 Synopsis of Other Relevant Water Quality Studies In the following, we present a concise overview of other studies describing data and analyses of temperature conditions in the Sammamish River system and their relevance to assessing Chinook salmon summer thermal refuge habitat in the river, and what can be done to improve conditions.

1.1.2.1 USACE FLIR study (McIntosh and Faux 2000) A Forward Looking Infrared (FLIR) study was performed of surface water temperatures on the Sammamish River on September 2, 1999 for the U.S. Army Corps of Engineers Seattle District. In the study, McIntosh and Faux (2000) wrote that surface water temperatures at the outlet of Lake Sammamish were the warmest in the entire river. Temperatures decreased downstream to the confluence with Bear Creek, which was almost 6oC cooler then the Sammamish River, with an immediate decrease in mainstem surface temperature of 1.7oC. Mainstem temperatures continued to decrease gradually downstream to a low of 16.6oC below Horse Creek. Recorded temperatures then increased slowly in the downstream direction to Lake Washington. Swamp Creek was suggested by the data to contribute to the general warming trend.

Ten tributaries were detected to contribute flow to the Sammamish River, with eight (including Bear Creek) contributing cooler flows. Eight of the tributaries had surface temperature plumes that were highly localized and confined to a small area, while both Bear Creek and Little Bear Creek had the largest plumes that extended more than 800 ft downstream. Only Bear Creek was concluded to have a significant effect on the long temperature profile of the Sammamish River, however. A few non-tributary locations were noted to contribute warmer water to the overall thermal environment, but in general there was a lack of thermal heterogeneity at the pool habitat unit scale (McIntosh and Faux 2000).

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1.1.2.2 King County Diel pH-Dissolved Oxygen Study of Sammamish River (DeGasperi 2005a) As part of efforts to develop hydrodynamic and water quality models of the river as part of the Sammamish-Washington Analysis and Modeling Program (SWAMP), the King County Department of Natural Resources and Parks (County) collected field data during the summer of 2003 to aid in the development of a model simulating diel temperature, dissolved oxygen, and pH dynamics in the Sammamish River (DeGasperi 2005a). The study confirmed previous findings that elevated river temperature and depressed DO concentrations in the river frequently did not meet state standard limits describing the impairment of salmon and trout migration and rearing. Highest water temperatures were recorded at the outlet of Lake Sammamish, and cooler temperatures occurred downstream. Maximum daily temperatures peaked in early August, at ~26°C upstream and ~24°C near Woodinville. DeGasperi (2005a) concluded that a synoptic temperature/conductance study should be conducted to identify significant surface and groundwater inputs to the Sammamish River.

1.1.2.3 King County CE-QUAL-W2 model of river (DeGasperi 2001, 2009) As part of development of SWAMP, the County adopted and further refined a CE-QUAL-W2 water quality model of the Sammamish River to evaluate future temperature management scenarios as part of the Sammamish River Corridor Action Plan development (DeGasperi 2001). This 2-dimensional (2-D) model simulates the vertical stratification of temperature averaged across the width of the river channel. The model has undergone a number of applications since the beginning of the decade.

The model initially represented the Sammamish River as 40 sub-reaches with each stratified into between eight and sixteen equal depth layers with number varying with sub-reach depth (DeGasperi 2001). Simulations focused on the August 1-October 31 adult Chinook salmon migration period and were based on weather and flow data from 1970-1999. An index of thermal stress was evaluated that represented the cumulative effects of exposure to elevated temperatures. The index was equal to the number of degree days that temperatures exceeded 17°C, a value recommended by DOE to support summer migration of Chinook and sockeye salmon. Modeling of alternative management scenarios indicated the following:

The best way to significantly influence temperature conditions in the warmest reach between Lake Sammamish and Bear Creek would be to withdraw water from cooler, deeper layers in the lake. This was predicted to reduce average and maximum thermal stress index values by roughly 66% and 35%, respectively.

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The next most effective method would be to revegetate riparian areas over the entire length of the river, although the benefit was greatest in the lower river where thermal stresses were modeled to be less severe.

Use of reclaimed water and groundwater augmentation were predicted to also provide significant reductions comparable to development of a fully mature vegetation corridor depending on the volume, temperature, and location of enhanced flow inputs.

Augmentation of summer flows in Bear Creek by 5 cfs and protection of riparian shading along the stream margin were predicted to significantly influence temperatures in the river immediately downstream of the confluence. DeGasperi (2009) described subsequent application and refinement of the model to further evaluate temperature management scenarios, and presented a more detailed review of the history of development actions and resulting temperature problems in the Sammamish River corridor. The number of sub-reaches was increased to provide greater model resolution and more detailed temperature and water surface elevation data were used for model calibration. The updated model was unable to simulate temperature increases very well in the lowermost portion of the river below North Creek where water levels are under a backwater influence from Lake Washington during the summer (water surface data used for calibration indicated a backwater effect extending upstream by more than 7 miles from Lake Washington). The reason for this result was not known, but it highlights the potential confounding effects of the lake on analyzing temperature mixing fields below North Creek.

1.1.2.4 King County 3-D Hydrodynamic Model of Lake Sammamish (DeGasperi 2008) The County has also been involved in the development of hydrodynamic water quality models of Lake Sammamish, including the 2-D CE-QUAL-W2 and a more sophisticated 3-D model, CH3D-Z. A key goal of the modeling is to simulate the temporal and spatial dynamics of water temperature in the Lake. In this report, DeGasperi (2008) documents initial calibration efforts and identifies where systematic seasonal, interannual, and spatial (primarily vertical) temperature prediction errors occurred. The data used to calibrate the model show a strong vertical temperature stratification in the upper 30+ ft of the water column, which is indicative of the strong controlling thermal effect lake surface waters have on temperatures in the Sammamish River.

1.1.2.5 King County Riparian Shade Assessment (DeGasperi 2005b) As part of developing the CE-QUAL-W2 model, the County collected riparian shade data along the Sammamish River in August and September of 2004 (DeGasperi 2005b). A key objective of the work was to determine if LiDAR data could be used to assess tree height remotely. Effective

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shade measurements were made at 57 locations along the length of the river for use in evaluating shade model predictions and their sensitivity to error in shade height. The analysis indicated that effective shade prediction errors were relatively insensitive to tree height errors on the order of +/- 50%. DeGasperi (2005b) concluded that the remotely sensed data exhibited some promise for use in ultimately modeling stream temperatures.

1.1.2.6 1998 Lake Washington Basin Adult Chinook Salmon Radio-Tracking Study (Fresh et al. 1999) As indicated above, the WDFW, MITFD, USFWS, and King County tagged adult Chinook salmon with ultrasonic radio-tags and tracked their migration in the Lake Washington basin from August through October, 1998. In the Sammamish River, stationary receivers were installed below the mouth of Swamp Creek and at the outlet of Lake Sammamish. A mobile tracking receiver was also used. Fish tagged at the Ballard Locks were observed to arrive at the mouth of the Sammamish at the end of August and the last fish detection in the river occurred at the end of October. This period was found in subsequent years to extend between late July and early November (E. Warner, MITFD, personal communication). Fish were observed to hold in a limited number of pools, with the greatest number of detections in two pools in Marymoor Park upstream of Bear Creek. The next largest number of detections occurred in a pool in the vicinity of the Tolt River pipeline crossing (called “winery pool”) and at the mouth of Swamp Creek. Fish were also detected at the mouth of Bear Creek and four other pools.

1.1.2.7 City of Bothell North Creek Confluence Study (R2 Resource Consultants 2009a,b) R2 Resource Consultants Inc. (R2) was contracted by the City of Bothell to assess summer water temperature conditions at the confluence of North Creek and the Sammamish River, and evaluate potential benefits and feasibility of channel modifications to expand the summer cool water mixing zone that occurs below the confluence. The overall intent was to find ways to retard mixing of cooler water from North Creek with warmer water in the Sammamish River during low flow, late summer months when adult Chinook salmon may be present, thereby increasing available refuge habitat space for fish that may elect to migrate upstream from Lake Washington before thermal conditions are more optimal.

A 2-dimensional (2D) hydrodynamic and temperature model was developed for use as a habitat restoration design tool. The model simulated depth, velocity, and temperature distributions in the confluence region during low summer flows based on channel morphology, hydraulic roughness, turbulent mixing characteristics, and flow and temperature inputs from upstream in the Sammamish River and North Creek. The model was calibrated to field flow and temperature data and used to evaluate effects of different alternatives involving structural and channel

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modifications within the Sammamish River, and correspondingly the feasibility of increasing habitat area suitable for adult Chinook salmon during the warm summer and early fall period.

Two metrics were assessed as a basis for evaluating potential effects of an action using the model: (i) area below the confluence with temperatures within a specified difference from that of North Creek; and (ii) area below the confluence with temperatures above selected threshold criteria for adult Chinook salmon (e.g., avoidance, stress, and death). Three structural modification options were suggested by the data and model to plausibly retard mixing and maintain a longer or larger area plume with cooler water: (i) Expanding the cool water area near the bottom by excavating into the right bank immediately below the confluence; (ii) Constructing a diagonal log or rock structure on the river bottom that guides low flows from the Sammamish River above the confluence to remain in the left half of the channel, and reduce the volume of warmer water flowing over the top of the cool water plume from North Creek; and (iii) Constructing stream-wise oriented structures, analogous to long, submerged piers on the river bottom running below the confluence along the toe of the right bank and to the left side of the North Creek plume, to retard mixing of the plume with the overflow to the right and the main flow to the left. Of these, the second alternative was selected for design, and CAD drawings were developed to the 30% level. The option was predicted to increase the area of cooler water habitat between approximately 10 ft2 and 340 ft2 depending on the temperature contour and ambient temperature of the Sammamish River (Figure 1-13).

1.2 OVERVIEW OF THIS STUDY AND REPORT OUTLINE This report documents a study funded by the Environmental Protection Agency (EPA) and managed by the MITFD. The overall goal of the study is to identify options to help improve water temperatures and channel structure, in order to develop and protect a future viable salmon migration corridor. The project results will help implement a high priority recommendation of the Sammamish River Corridor Action Plan to create and enhance pools in the river channel to provide cool water refuge and cover, particularly for adult salmon migration. It will partially implement a priority project in Lake Washington/Cedar/ Sammamish Watershed Chinook Salmon Conservation Plan entitled “Sammamish River Tributary Mouth Restoration Feasibility Study.” Recent and ongoing regional water resource plans contemplate reclaimed water uses to augment aquifer and stream recharge and water supply source exchange projects to restore tributary flows. While tree plantings and habitat restoration have occurred at selected locations, especially near the cities of Redmond and Woodinville, more work is needed to improve this important salmon migration corridor. While the present study emphasizes thermal refuge habitat for the adult migration phase, implementation of prioritized projects would contribute to increased habitat complexity and improve rearing habitat opportunity for all life stages.

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341 127

100 ) ) 2 80 60 40 20 0 -20 17.5 18 18.5 19 19.5 20 20.5 21 21.5 -40 -60 Sammamish R Temp = 20 C

Within 0.5C Below Abscissa Value Within (ft Abscissa Below 0.5C -80 Sammamish R Temp = 22 C Change in Area With Water Temperature Temperature inWith Water Change Area -100 -535 -231 Temperature (C) Figure 1-13. Predicted changes in surface area between consecutive isothermal contour lines for depth- averaged water temperatures in the Sammamish River (108 cfs) after constructing the proposed alternative. Simulated upstream water temperatures were 20ºC and 22ºC for the Sammamish River (i.e., two model runs), and 17.3ºC consistently for North Creek (18 cfs). Each histogram bar represents the post- minus pre-project difference in area bounded between isothermal contour lines for the labeled temperature (Ti) and the next lower temperature (Ti-1 = Ti-0.5°C). The negative bars for the 20°C and 21.5°C contours reflect areas of the stream that become cooler with the project (i.e., = „lost‟ area; Figure copied from R2 2009b).

R2 was contracted by the MITFD to conduct the study, which involves assessing thermal refuge habitat availability in the Sammamish River and identifying specific locations and measures whereby such habitat may be enhanced. Key project objectives included:

Collecting data regarding the locations, volume, and extent of existing thermal refuge areas in the Sammamish River, with a primary focus on assessing the relationship between tributary inflow volumes and these areas;

Developing a relative priority ranking of tributary mouths and other significant groundwater input locations as candidates for thermal habitat restoration based on temperature, hydraulic, hydrologic, and other site characteristics and feasibility; and

Prepare conceptual designs and preliminary cost estimates for the highest priority thermal refuge habitat restoration sites to assist local governments or other potential project future sponsors, and prepare a minimum of one final design for future permitting and construction.

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This report is accordingly organized into the following sections:

Section 1 is this Introduction

Section 2 describes the field data collection and analysis methods used to identify candidate thermal refuge habitat locations via a streamwise (longitudinal) profile of surface and near bottom temperatures, selection of sites for detailed sampling, measurement of 3-dimensional (3-D) temperature fields and bathymetry for computing volume of thermal refuge habitat available, and measurement of flows.

Section 3 describes the results of the field data collection and analysis, including a longitudinal profile of surface and near-bottom temperatures, the identification of candidate sites for detailed temperature measurements based on the longitudinal profile results, and the resulting detailed site data. The detailed site temperature data are used to help rank sites for restoration potential in Section 4 and in evaluating the potential benefits of tributary flow augmentation as described in Section 6.

Section 4 summarizes the factors influencing feasibility and benefits of potential thermal habitat refuge improvement at all sites visited, and ranks them based on the extent of influence on mainstem temperature conditions, site physical characteristics, site constraints influencing constructability and cost, factors influencing longer term pool maintenance including bedload transport concerns, public safety, and other factors. The five best sites are identified for further consideration in Section 5.

Section 5 presents conceptual designs for the five highest ranking sites for potential project alternatives, with between 1-3 alternatives identified per site based on site characteristics. Alternatives considered include construction of instream structures, and/or physical modification of channel morphology including changes to bathymetry and channel width, and opportunities for physical and riparian cover restoration. Scoping level cost estimates are also presented and potential design and construction constraints are identified.

Section 6 discusses the potential effects of increasing summer tributary flows on refuge habitat availability by (i) relating the 3-D temperature field data for all sites with flows in the tributaries and Sammamish River, and (ii) using the 2-D hydrodynamic model developed for the site selected for detailed design in Section 5.

Section 7 discusses the findings of this study and summarizes relevant conclusions.

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2. TEMPERATURE ASSESSMENT METHODS

Data collection efforts were conducted on the Sammamish River during the summer of 2010 to identify and assess locations and extent of existing thermal refuge areas. Three distinct field data collection efforts occurred: 1. The first effort involved developing a longitudinal profile of water temperatures in the second half of July 2010 when water temperature exiting Lake Sammamish finally warmed up to above 20°C. Data from the longitudinal profile field effort were used to identify sites for more detailed temperature profile sampling. 2. The second field effort entailed more detailed synoptic sampling in August and September 2010. The goal was to collect three-dimensional (3-D) temperature and flow data that can be used to quantify empirically the relation between flow and water temperatures, and lead to identification of sites with larger thermal mixing zones that would be the best candidates for future thermal refuge habitat restoration work, and for selecting locations for more detailed conceptual and designs. 3. The third field effort involved collecting more detailed bathymetry data in the fall for developing a final design for the highest ranking site and for evaluating effects on flood flow water levels for meeting a no-rise criterion. The detailed 3-D temperature field and flow data measured as part of the second effort were found to be sufficient for calibrating a 2- dimensional (2-D) hydrodynamic temperature model. Because this part of the study was associated strictly with the later design phase of the project, the methods and results are discussed in Section 6.0 instead of Sections 2 and 3.

Data for the first two efforts were collected during the afternoon on days when the river temperature exceeded 20°C. This relative low threshold for sampling reflected the unfortunate incidence of 2010 proving to be a cool year overall, with few days having river water temperatures exceed 23°C. In order to get as many sites sampled as possible, it was necessary to lower the threshold temperature for sampling from the original target level of about 23°C. Temperature measurements generally began around 2 pm in the afternoon and continued as late as 8 pm on a few days depending on the extent of the thermal mixing zone. This timing reflected data describing general diurnal variation in river temperatures, with the intent to sample during the warmest time of the day and maximize consistency in spatial temperature distributions to the extent practicable (Figure 2-1).

Details follow on the specific equipment and methodologies used in this study.

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22 Sammamish River North Creek

21 C) ° 20

18 WaterTempertaure (

16 8/7/08 12:00 AM 8/7/08 6:00 AM 8/7/08 12:00 PM 8/7/08 6:00 PM 8/8/08 12:00 AM

Figure 2-1. Example daily variation in water temperature in the Sammamish River and North Creek, and general time period in which longitudinal and detailed site temperature profile sampling of water temperatures occurred, indicated by the arrows.

2.1 TEMPERATURE MEASUREMENT Water temperature measurements were collected using either a Hydrolab Quanta for spot measurements or an Onset Pro V2 for continuous measurements. Table 2-1 provides a list of the temperature equipment used and data quality indicators. A pre- and post-calibration check was conducted for each unit before and after data collection.

Table 2-1. Field measurements and data quality indicators used on this project. Parameter Method Precision Sensitivity1 Water Temperature Hydrolab Quanta ≤20% RPD2 ± 0.2°C (spot measurements) Water Temperature Not applicable since (continuous Onset Pro V2 duplicate data will not be ± 0.2°C measurements) collected Not applicable since Swoffer 2100 ± 1% Velocity duplicate data will not be ± 2% Marsh McBirney Flo-mate 2000 collected 1 Instrument Specifications. 2 Relative Percent Difference, ensured by using the same temperature probe for all spot measurements.

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2.1.1 Calibration Pre- and post-field work calibration tests were conducted on all of the temperature instruments used for data collection including four Onset water temp pro V2 continuous loggers and one Hydrolab Quanta. The pre-data collection calibration was conducted on July 7, 2010. Eleven water temperatures were measured between approximately 6°C and 30°C and compared with the results from a certified reference thermometer. The pro V2 loggers were set to record temperatures every minute and the time of the reference thermometer reading was recorded. All of the instruments were placed in a standard five gallon bucket. Weights were clipped on to the continuous loggers so they would be suspended in the water column, and not floating on the surface. Tap water and ice packs were added to the bucket and several temperature measurements were collected over a three hour period. Warm tap water was then added to the bucket and an additional four measurements were collected over a two hour period. Note that the water in the bucket was not thoroughly mixed for the first and eighth data points collected; this was noted when the reference thermometer was inserted into the bucket for measurement and a temperature change from the top of the bucket to the bottom was observed.

The post-data collection calibration was conducted on October 5, 2010. Ten water temperatures were measured between approximately 15°C and 35°C. Tap water was added to the bucket and the temperature recorded. Hot water from the tap was added and four water temperatures measured over a four hour period. Additional cold water from the tap was added and five more temperatures were recorded over a three hour period.

Results from the pre-data collection test are provided in Figure 2-2 and Table 2-2. As seen in Table 2-2, most measurements have a difference of 0.2°C between the instrument and the reference thermometer which is within the accuracy of both the pro V2 loggers and the Quanta. All instruments were deemed within the manufacturer‟s reported specification and determined to be appropriate for use on this project.

Results from the post-data collection test are provided in Figure 2-3 and Table 2-3. As seen in Table 2-3, most measurements have a difference of between 0 to 0.1°C between the instrument and the reference thermometer which is within the accuracy of both the pro V2 loggers and the Quanta. Some larger differences were recorded. However, these differences were recorded during periods of rapid change in temperature and can be attributed to several factors. The bucket may not have been uniformly mixed. This is evidenced by the small changes observed in the continuous logger during periods of data collection. There may also be a slight lag in temperature recorded by the loggers and the actual temperature. And finally, the time recorded

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for the reference thermometer and the continuous loggers may be off by 1 to 2 minutes. Given that the water temperatures collected on this project do not change that quickly and the difference in temperatures were within specifications during periods of stable or slowing changing temperatures, it is assumed that the data collected by these units are accurate and no adjustments to the data collected are necessary.

Temperature Instrument Calibration Results - July 7, 2010

25 2023228 2023229 2023230 20 2023231 Hydrolab Thermometer 15

Temperature(Celsius) 10

7/7/10 1:00 PM 7/7/10 2:00 PM 7/7/10 3:00 PM 7/7/10 4:00 PM 7/7/10 11:00 AM 7/7/10 12:00 PM

Time Figure 2-2. Comparison of temperature calibration results for the pre-field work test conducted on July 7, 2010.

2.1.2 Grab Samples/Temperature Profiles Spot measurements and temperature profiles were collected using the Hydrolab Quanta. The Quanta was submersed at the desired location/depth and allowed to equilibrate. Once the unit was reporting a stable value, the value was recorded in °C in the field book or on the field form. Values were reported to the nearest tenth. In some instances water temperatures were not stable and in these cases the average value observed was recorded.

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Table 2-2. Difference in reference thermometer and temperature instrument measurements for the first calibration test on July 7, 2010. Reference Thermomete Instrumen Instrumen Instrumen Instrumen Data r t 2023228 t 2023229 t 2023230 t 2023231 Quanta Poin Temperature Difference Difference Difference Difference Differenc t (°C) (°C) (°C) (°C) (°C) e (°C) Notes Not thoroughl 1 18.2 -1.1 -1.0 -0.9 -0.9 0.0 y mixed 2 8.9 -0.2 -0.1 -0.1 -0.1 0.0 3 8.8 -0.1 -0.1 0.1 0.1 0.2 4 6.5 0.1 0.0 0.1 0.2 0.1 5 6.5 0.2 0.1 0.0 0.2 0.1 6 7.7 0.3 0.3 0.2 0.3 0.1 7 8.4 0.4 0.3 0.4 0.4 0.1 Not thoroughl 8 32.2 1.6 1.4 1.5 1.4 0.1 y mixed 9 30.7 0.1 0.1 0.1 0.2 0.2 10 29.7 0.1 0.2 0.1 0.1 0.2 11 26.4 0.0 0.0 0.0 0.0 0.1

2.1.3 Continuous Temperature Loggers Continuous temperature data loggers were installed at three locations distributed from upstream to downstream in the Sammamish River to adjust data if needed and to compare with the real time King County gage located at NE 116th Street. One logger was placed near the gage, another underneath the SR 520 bridge above Bear Creek, and the third in a shaded region of the left bank upstream of the confluence with Little Bear Creek. A fourth logger was placed in North Creek. The loggers were Onset HOBO Water Temp Pro V2 logger set to record the temperature every 30 minutes. The loggers were encased within a PVC pipe for protection, where the pipe was drilled with holes to ensure equilibration with the surrounding water. The pipe was filled with rocks to make sure the unit would sink and not move along the base of the channel. The tube was attached with a cable to a stable base sufficiently outside of the expected high flow during

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the sampling period such as a tree or a fencepost. Temperature loggers were installed in the end of July or beginning of August 2010 and all units were retrieved on September 21, 2010.

Temperature Instrument Calibration Results October 5, 2010

35 2023228 2023229 30 2023230 2023231 Hydrolab Reference 25

15 Temperature(Celsius) 10

10/5/10 9:00 AM 10/5/10 1:00 PM 10/5/10 2:00 PM 10/5/10 3:00 PM 10/5/10 4:00 PM 10/5/10 10:00 AM 10/5/10 11:00 AM 10/5/10 12:00 PM Figure 2-3. Comparison of temperature calibration results for the pre-field work test conducted on October 5, 2010.

2.2 LONGITUDINAL PROFILE SAMPLING The longitudinal variation in near-bottom and surface water temperatures was measured at discrete points along the length of the Sammamish River at a spatial resolution sufficient to identify locations of significant cooler water input. The goal of the effort was to identify the most significant potential thermal refuges from both tributary and groundwater inflows, to assist in selecting more detailed study sites.

Longitudinal survey data were collected over the first summer warm period between July 26, 2010 and July 29, 2010 (Table 2-4). Prior to this time the weather had been cool and Lake Sammamish was taking longer than usual to warm. The Sammamish River was floated between Lake Sammamish and Lake Washington using a 2-person kayak. Temperature measurements were collected on the surface and the bottom of the river, near the center of the channel at regular

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intervals spaced every 335 feet on average. Actual measurements depended on stream bottom morphology, with longer spacing occurring in straighter reaches with a prismatic channel where Table 2-3. Difference in reference thermometer and temperature instrument measurements for the second calibration test on October 5, 2010. Reference Instrument Instrument Instrument Instrument Thermometer 2023228 2023229 2023230 2023231 Quanta Data Temperature Difference Difference Difference Difference Differenc Point (°C) (°C) (°C) (°C) (°C) e (°C) Notes 1 15.8 0.1 0.0 -0.1 0.0 0.0 It is likely the bucket was either not fully mixed or there is a slight delay in the temperatures registered by the continuous 2 34.3 1.3 1.1 1.3 1.1 0.2 logger. 3 31.9 0.4 0.5 0.5 0.6 0.2 4 28.4 0.3 0.3 0.3 0.3 0.2 5 25.1 0.1 0.0 0.1 0.1 0.1 Same comment as 6 19.9 -2.2 -2.2 -2.2 -2.1 0.1 points 2-4 7 19.0 0.0 0.0 0.0 0.0 0.1 8 18.2 0.0 0.0 0.1 0.1 0.1 9 18.0 0.0 0.0 0.0 0.0 0.1 10 17.9 0.0 0.0 0.0 0.0 0.1 uniform flow conditions preclude significant pool formation and maintenance. With one exception, the longest intervals between measurements occurred in reaches with no tributary inflow and minimal geomorphic potential for significant pool formation. The longest interval (1,400 feet) was collected upstream and downstream of an overgrown, un-floatable portion of the river where boater safety was an issue. Measurements were collected over shorter distance intervals (minimum of five feet) (i) in the vicinity of tributaries and sharp river bends where pools are most likely to occur, and (ii) in the vicinity of Woodinville and Bothell where the

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Sammamish River valley converges and the river transitions from a wide alluvial valley to a more confined channel such that potential groundwater input rates may be higher than upstream. Table 2-4. Summary of Sammamish River longitudinal profile survey dates and conditions. Range in Air Temperature during Reach Date Sampled Data Collection (°C) GPS Coordinates 1 7/29/2010 61.8-70.1 288-304 2 7/26/2010 74.4-80.4 60-130 3 7/27/2010 70.6-77.8 132-212 4 7/28/2010 63.7-71.8 215-287

Stream flow and water temperature measurements were also collected in the mouth of tributaries. Temperature measurements were collected approximately 100 feet upstream of a tributary, at the mouth of the tributary, and at three successive locations downstream if the tributary caused a measurable impact to the temperature. At sites near tributaries, temperatures were collected at approximately one quarter of the width of the channel on the side nearest to the tributary.

Temperature was measured using the Hydrolab Quanta in °C. The probe was placed approximately half a foot below the water surface and allowed to equilibrate before the temperature was recorded, followed by a second near bottom measurement in the river. Note that data were recorded to the hundredth, but reported to the nearest tenth. The depth was recorded from the Hydrolab Quanta in meters. The location of each measurement was recorded using a Garmin hand held Global Positioning System (GPS) device. The accuracy of the GPS was generally less than 49 feet and depended on the number and location of satellites detected. Locations were stored in the handheld GPS unit using waypoints that were noted on data sheets with the stream temperature data. Differential correction with a GPS base station was not considered necessary because the precise location was not as important as identifying the general location of cooling; more precise differentiation of location of cooling was established as part of the detailed sample site temperature surveys. A field form was maintained with all of the data collected. This form included an entry for each data point on the point identification number, location of GPS coordinates, time of data collection, depth, surface temperature, bottom temperature, and comment.

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2.3 DETAILED SAMPLE SITE SELECTION Sites were selected for detailed temperature profile sampling based on the longitudinal temperature profile and flow data. An initial list of candidate sites was developed in consultation with the MITFD based on streams listed in Williams et al. (1975). Additional candidate sites were identified based on stream GIS coverages available on the City of Redmond and City of Woodinville websites, and an on-the-ground reconnaissance visit (Table 2-5). A mixing index was computed for each tributary junction as a key indicator for identifying those tributaries with the greatest potential for temperature moderation in the mainstem channel. The index was based on a first order analysis using flows and temperatures in the tributary and in the Sammamish River and applying the mass-concentration balance equation:

where Q = flow and T = temperature. The mixing index was calculated as the difference between the upstream Sammamish River temperature and the downstream mixed temperature. Review of data collected as part of previous work conducted by R2 (2009 a,b) at the mouth of North Creek suggested an approximate screening level criterion, where temperature modification at tributary confluences was considered to be most feasible in cases where the downstream value of Tmix is cooler than the upstream TSammamish by approximately 0.1°C or more. This threshold reflects professional judgment: a value on the order of 0.3°C was calculated for the date depicted in Figure 2-1, where a modest amount of temperature refuge habitat improvement was predicted to be feasible (R2 2009a,b). This threshold criterion was therefore used as an initial screening level check of feasibility for biologically meaningful temperature modification.

Smaller tributary sites that generally did not meet this threshold were then identified in consultation with the MITFD and visited in the field. A subset of sites with relatively larger mixing index values (but below the threshold) was selected to increase the range and sample size of sites for assessing the relation between flows and temperatures empirically (Section 2.4). The index results were also compared with modeling results produced by King County (DeGasperi 2009) to assist with identifying candidate sites.

A threshold for identifying candidate pools was more difficult to define in the absence of detailed data. The longitudinal profile data was reviewed but no significant pools were discerned. Data from the 1998 radio-tracking study (Fresh et al. 1999, E. Warner MITFD, unpublished data) were reviewed, and the deepest pools where fish were observed to hold were

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identified for consideration. Greater emphasis was placed on selecting one or more pools in the alluvial reaches upstream of Little Bear Creek, where risks to infrastructure, private property, and motorized boating are lower than downstream. In addition, there is evidence of multiple cool water springs providing thermal refuge locations below North Creek, where instream construction activity could have a higher risk of impacting a local aquifer (Andy Loch, City of Bothell, 2008 personal communication to P. DeVries). It was considered more strategic to provide additional thermal refuge farther upriver where such habitat may be less frequent than below North Creek. The strategy was based on the premise that it would be beneficial to distribute thermal refuge habitat for adult Chinook salmon more evenly along the length of the Sammamish River as they migrate upstream.

Table 2-5. Candidate Sammamish River tributaries for synoptic temperature-flow sampling based on the WDFW Puget Sound stream catalog (Williams et al. 1975) and other information. WDFW GPS coordinates Stream Code Site Name (Datum: NAD83) Location Description N47.754168 0059 Swamp Creek River mile 0.6 on right bank W122.241671 N47.748113 Approximately river mile 2.2 on left 0067/0066 Unnamed Tributary W122.213743 bank N47.747842 Approximately river mile 2.3 on left 0068 Horse Creek W122.210972 bank, flows through Wayne Golf Course N47.753025 Approximately river mile 4.2 on left 6900 Unnamed Tributary W122.190187 bank N47.756290 0070 North Creek River mile 4.35 on right bank W122.188908 N47.754779 0080 Little Bear Creek River mile 5.4 on right bank W122.168865 Unnamed Tributary N47.741745 0088 (assumed Gold River mile 6.55 on right bank W122.153385 Creek) N47.735589 na Derby Creek River mile 7.25 on right bank W122.147558 N47.7325381 0090 Unnamed Tributary River mile 7.3 on right bank W122.147194 N47.732763 Approximately river mile 7.5 on left 0091 Unnamed Tributary W122.145742 bank, upstream of NE 145th Street

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Table 2-5. Candidate Sammamish River tributaries for synoptic temperature-flow sampling based on the WDFW Puget Sound stream catalog (Williams et al. 1975) and other information. WDFW GPS coordinates Stream Code Site Name (Datum: NAD83) Location Description N47.728606 0095 Unnamed Tributary River mile 8.0 on left bank W122.143303 River mile 8.8 on right bank upstream of N47.710547 na Unnamed Tributary NE 124th Street, at Hollywood Pump W122.142503 Station N47.699427 0099 Unnamed Tributary River mile 9.8 on left bank W122.144580 N47.696814 Approximately river mile 9.9 on left 0100 Unnamed Tributary W122.141691 bank N47.695502 Approximately river mile 10.1 on right 0101 Unnamed Tributary W122.139580 bank N47.689526 0102/0103 Unnamed Tributary River mile 10.6 on left bank W122.134508 N47.683392 0104 Peters Creek River mile 10.95 on left bank W122.132531 N47.668014 0105 Bear Creek River mile 12.2 on right bank W122.126498 N47.654692 Approximately river mile 13.3 on left 0141 Unnamed Tributary W122.112403 bank near Rowing Club dock N47.653722 Approximately river mile 13.5 on left 0142 Unnamed Tributary W122.110481 bank, near Rowing Club

2.4 FLOW MEASUREMENT Stream discharge measurements were collected in the Sammamish River and the four largest tributaries by extending a fiberglass open reel tape across the stream channel. A water depth and velocity was collected at roughly 20 or more cells along the wetted length of the tape. The water‟s edge and discharge transect stationing were measured on the tape to the nearest 0.1 foot. Water depth was measured using a top-setting wading rod to the nearest 0.1 foot in channels wider than 20 ft, and 0.05 ft in narrower channels. Velocity measurements were collected using either a Marsh McBirney Flo-Mate velocity meter set in the fixed-point averaging mode, or a calibrated Swoffer Model 2100 velocity meter set in display average mode at 20-second intervals. Water velocity was measured at 0.6 of the depth for stations with water depth less than 2.5 feet, and at 0.2 and 0.8 of the total water depth for stations with water depths greater than 2.5

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feet. The Marsh McBirney sensor and Swoffer propeller were oriented perpendicular to the transect line. The angle from the transect line was recorded where the flow pattern for that station was not within approximately 10 degrees from perpendicular to the transect line. Swoffer velocity data were adjusted using calibration curves derived specifically by R2 in laboratory tests for the meter used.

Various alternative methods were used to estimate order of magnitude of flow in very small tributaries where the net flow contribution to the Sammamish was approximately 5% or less. In the largest of these, a section was selected with as hydraulically smooth a velocity distribution across the channel as possible and depth and velocity measurements made at between 0.5 ft and 1.5 ft intervals. Where a tributary flowed out of a culvert or over a weir, 1-2 velocity measurements were made to estimate the mean velocity of the outfall and discharge calculated as the product of mean velocity, depth, and width of the section. In a few cases, a 5-gallon bucket was used with a stop watch to measure the time to fill, with three replicates sampled from which an average flow rate was calculated.

2.5 DETAILED SITE TEMPERATURE FIELD DATA COLLECTION The 3-D temperature field was measured on 1-2 occasions at each detailed sample site ultimately selected (Figure 2-4), with the total number of days of sampling constrained by a cooler summer than usual. The goal of the sampling was to collect enough bathymetry and temperature profile data to estimate temperature contours and volumes either directly in three dimensions depending on availability of commercial software allowing 3-D gridding, or in two dimensions at each depth layer and then summing across layers (a pseudo-3-D approach).

2.5.1 Field Data Collection Three local temporary benchmarks were established at each site using rebar to provide redundant horizontal and vertical survey control. The horizontal coordinates and elevations of the benchmarks were determined using a Sokkia SET5 total station, which was set on top of one of the three benchmarks the coordinates of which were arbitrarily set at (1000, 1000, 1000) with units in feet. The survey “north” line was set by shooting to one of the two benchmarks first. Horizontal coordinates and elevation were then surveyed at numerous points in the channel and long the water‟s edge on the tributary side to define the 3-D temperature mixing field and water surface elevation.

At each survey point, the vertical water temperature profile was measured using the Hydrolab Quanta probe. Temperatures were measured at the surface and bottom, and in increments of 1 ft

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from the surface at all sites except Swamp Creek, where 2 ft increments were used because of the deeper water there. The number of vertical temperature profile data points ranged from one (1) in shallow water to seven (7) in deeper water.

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Lake Washington

Lake 1.5 1.5 Sammamish Miles

Figure 2-4. Location of detailed temperature measurement sites within the Sammamish River basin.

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Data were collected with smaller spacing between points across the channel and longer spacing in the stream-wise direction in consideration of the properties of the mixing zone, which tended to be elongated and have a steeper temperature gradient cross-channel than upstream- downstream. The spatial horizontal distribution of points needed was determined iteratively as the day proceeded. In general, data collection started at the tributary confluence and proceeded as a series of cross-section passes, working progressively in the downstream direction. The lateral (cross-channel) and stream-wise extent of the survey was controlled by temperature magnitude, where sampling ceased in each direction once all point measurements in the water column exceeded 20°C. This was selected as a strategic cutoff point defining the approximate extent of the mixing zone and was necessary because there was not enough time to continue measuring the entire extent of the mixing zone before temperatures dropped substantially in the evening. It also represents a reasonable upper limit to suitable water temperatures for holding adult salmon (see Section 1.1.1.3), where defining the temperature mixing field at higher temperatures is less biologically meaningful in the context of evaluating measures to expand thermal refuge habitat.

The total station automatically recorded the survey coordinate data, and a field data sheet was used to record survey coordinate (for backup), depth, and temperature data. Flow data were collected in the Sammamish River either upstream or downstream of the tributary, and in the tributary and recorded in field books. All written data were photocopied upon return to the office.

2.5.2 Analysis The coordinate data were downloaded from the total station as northings, eastings, and elevations and with the depth and temperature data entered from the data sheets into Excel spreadsheets. The hand-written data sheet coordinate data were used to ensure the depth and temperature data were associated with the correct downloaded coordinate data for each survey point. The spreadsheets were then QA/QC‟d and data entry errors corrected. In one case, the total station benchmark was found to have sunk slightly between the first and second sample event, and the elevation data were corrected accordingly for the second sample. The coordinate, depth, and temperature data were then exported to an ASCII text file, and processed using a Fortran program written to output the data in a format permitting most efficient and consistent processing through a contouring software package.

Two different software programs developed and sold by Golden Software, Inc. were considered as being most applicable and were evaluated for potential use in this project. The first was Voxler 2, which allows gridding in three dimensions. After sending trial datasets to a technical

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support programmer at Golden Software, it was determined that the package was not sufficiently robust or accurate for purposes of this project. The gridding resulted in 3-D “bubbles” and could not smooth the data sufficiently while remaining true to the temperature values of the original data points. The second package, Surfer 9 was found to work more effectively and was thus used to create temperature contours at each depth layer, with the goal of then summing the area enclosed within each temperature contour across layers to obtain an estimate of the total volume of water with temperatures less than a specified level.

There were two steps to the analysis using Surfer. Input data files were created for each site containing the (X, Y, Z) topographic survey point data from each sampling date. At sites sampled twice, the topographic survey point data were combined to use all of the data to define bathymetry. The combined data were read by Surfer and gridded using the Kriging method. This was found after an initial trial and error evaluation of the numerous gridding options available in Surfer to provide realistic looking elevation contours while remaining sufficiently faithful to the raw data elevation distribution. A blanking polygon was defined for the landward side using the water‟s edge data to help keep resulting contour lines smoother looking near the boundary. Bathymetric contour lines were then created in 1 ft increments starting at the water surface elevation for the date for which temperature data were to be analyzed, down to below the deepest point at which data were collected. These elevation contour lines were necessary to define blanking files for the subsequent contouring of water temperatures so that the streambed boundary could be adequately represented, and temperature contours would thus not be analyzed in the summation of area as if they extended past the streambed boundary. For example, if the water surface elevation for a given sampling date was 997.2 ft and the maximum depth sampled was 4.6 ft, elevation contour lines would be developed for the 997.2, 996.2, 995.2, 994.2, 993.2, and 992.2 ft levels. The 997.2 contour line was analyzed with the surface layer temperature data, the 997.2 ft and 996.2 contours were analyzed with the 1 ft depth layer temperature data, etc.

The temperatures measured in a given depth layer (either surface, 1 ft down, 2 ft down, etc.) were then input into Surfer with the respective horizontal coordinates for each point where a temperature (T) was measured in that layer. A blanking line was specified equal to the coordinates (X,Y) of the streambed elevation contour bounding that depth layer. The combined (X,Y,T) data were read by Surfer and gridded using either the modified Shepard‟s or Kriging algorithm with the most realistic looking fit selected.

Temperature contours were then plotted in Surfer corresponding to +1°C, +2°C, etc., up to a maximum of +6°C above the influent tributary temperature. The area contained within each temperature contour was determined, and added across depth layers to yield an estimate of the

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total volume within the mixing zone bounded by each level of temperature increase from the influent temperature. For all sites except Swamp Creek, the surface temperature layer represented the upper 0.5 ft deep slice of the water column, and the remaining temperature layers a 1 ft deep slice. At the Swamp Creek site, the surface layer was measured as 1 ft thick and lower layers 2 ft thick. The results were used to help rank sites for restoration potential (see Section 4), and analyzed for their relation with flows in the tributary and mainstem to evaluate potential benefits associated with flow augmentation in tributaries (see Section 6.1).

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3. RESULTS OF FIELD ASSESSMENTS

The spring of 2010 was generally one of the cooler springs on record, resulting in delayed warming of Lake Sammamish. In addition, there were few extremely hot spells during the summer resulting in measurement of temperature conditions closer to average (Figure 3-1). Water temperatures in the Sammamish River were typically below 22°C on most days, and reached 23°C on only 7 days total. The continuous recording temperature loggers placed in the Sammamish River and North Creek produced data that mirrored the Sammamish River gage data (Figure 3-2). The difference in water temperature measured by the County at Station 51T and our logger placed in close proximity to the gage were generally within measurement error.

Sammamish River Station 51T

24 Observed Minimum Observed Mean Observed Maximum 22 Historical Monthly Mean

Temperature(degrees Celcius) 14

10 1-Apr 1-May 1-Jun 1-Jul 1-Aug 1-Sep

Figure 3-1. Observed water temperatures in the Sammamish River for April through September 2010.

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Sammamish River Temperature Study Continuous Monitoring Sites

18 Temperature(C)

Sammamish River above Bear Creek (2023231) 14 Sammamish River @ 116th St (2023228) Sammamish River above Little Bear Creek (2023230) North Creek (2023229) 12 7/1/10 7/15/10 7/29/10 8/12/10 8/26/10 9/9/10 9/23/10

Sammamish river Continuous Data Comparison

Sammamish River @ 116th St (2023228)

22 King Co Gage 51T at 116th St

16 Temperature(C)

10 8/1/2010 8/15/2010 8/29/2010 9/12/2010 9/26/2010

Figure 3-2. Observed temperature in the Sammamish River at R2‟s continuous monitoring sites (top), and comparison with the King County gage at Station 51T located near NE 116th St.

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3.1 LONGITUDINAL PROFILE Data collected during the longitudinal profile survey are provided in Figure 3-3. The distance downstream was measured as a function of the most upstream point where data were collected, at the outlet of Lake Sammamish. Because temperature sampling focused on finding cool water inputs, the depths at tributary locations with local drops in temperature reflected the depth of the measurement made near the mouth of a tributary, not necessarily the river thalweg.

There are three breaks depicted in the temperature profile data reflecting data being collected over a four day consecutive period. While the temperature data collected on one day cannot be compared directly to data collected on another day because of daily variation, it is the relative difference on a given date that matters for discerning locations of local cooling. Accordingly, the longitudinal profile data indicate reductions in mainstem temperature downstream of seven primary tributaries including: Swamp Creek, Horse Creek, North Creek, Little Bear Creek, Gold Creek, Bear Creek, and Site 0142. An overview of the measured upstream, tributary, and downstream temperatures for these sites is provided in Table 3-1. Flow reductions were generally not significant at the other tributary locations. A suitable location for flow measurement could not be found for four of the original 18 tributary candidates: 0067/0066, 0099, 0100, and 0141, so temperatures were taken at the approximate location indicated in the WDFW stream catalog (Williams et al. 1975).

Figure 3-2 indicates that the near-bottom temperature above the weir at the upstream end of the river was found to be slightly cooler than the surface on July 29, 2010, which most likely reflects stratification of Lake Sammamish and the topographic control imposed by the weir. The thermal influence of stratification in Lake Washington is also evident in the figure, with an approximately constant near-bottom temperature extending upstream to approximately the location of Horse Creek. There is also some minor, near bottom cooling evident between Horse Creek and North Creek, which may reflect the influence of diffuse springs in that mostly confined reach. No pools were found upstream of North Creek that exhibited a significant vertical temperature stratification or local cooling influence near the bottom.

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7/29 - Surface Sammamish River Longitudinal Profile 7/29 - Bottom 7/26 - Surface 7/26 - Bottom 7/27 - Surface 7/27 - Bottom 24 7/28 - Surface 25 7/28 - Bottom Tributary Temperature 23 Depth

22 20

20 15 (Trib below 124th)

(Horse Creek) (ft) Depth 18 (North Creek) 10 (Little Bear Creek) Temperature (degC) (Swamp Creek) (142) (Bear Creek) 17 (Unmarked)

16 5

(104) (Gold Creek) 15 (102) (101) (6900) 14 (090) 0 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 Distance Downstream (ft)

Figure 3-3. Longitudinal profile measurements made July 26-29, 2010 of surface and near-bottom water temperatures, and corresponding depth at measurement location, in the Sammamish River. Tributaries are identified by name/WDFW stream catalog number (Williams et

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al. 1975) and temperature during the survey. Note that depressed temperatures at tributary locations reflect measurements nearer the mouth, not necessarily river thalweg.

Table 3-1. Summary of temperature drops observed during the longitudinal profile data collection Sammamish River Sammamish River Upstream Downstream/Mouth Temperature Temperature (C°) Tributary (C°) WDFW Temperature Stream Code Location Surface Bottom (C°) Surface Bottom Comment 0059 Swamp Creek 22.9 22.7 17.9 22.4 19.3 Just downstream toward right bank 0068 Horse Creek 21.5 21.5 18.70 21.1 Just downstream toward left bank 0070 North Creek 22.4 22.4 18.41 22.2 18.9 Near mouth of creek Little Bear 50 feet downstream toward right 0080 Creek 22.5 22.5 18.06 22.5 bank 0088 Gold Creek 22.4 22.4 15.41 19.7 19.8 Just downstream toward right bank 0105 Bear Creek 23.5 23.5 16.75 21.5 19.5 Just downstream toward right bank Unnamed 0142 Tributary 22.9 22.6 17.20 18.6 Near mouth of creek

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3.2 SAMPLE SITE SELECTION Using the longitudinal profile data, five sites met the mixing index threshold criterion of 0.1°C described in Section 2.3 that qualified them for more detailed temperature field measurements: Swamp Creek, North Creek, Little Bear Creek, Gold Creek, and Bear Creek (Table 3-2). It was decided to increase the sample size and range of temperature and flow conditions by adding several of the smaller tributary sites. Several sites were recommended for sampling based on observed temperature drops and/or professional judgment. Although the calculated mixing index values indicated negligible influence on temperatures in the Sammamish River, Tributary 0142 and Horse Creek were added because a local temperature influence was observed nonetheless. Tributary 0091 was selected for detailed sampling because of the perceived potential for enhancing temperatures under the NE 145th Street bridge which provides shade cover (see Section 4). Tributary 0090 and Derby Creek were added because they could be sampled quickly on the same day as Tributary 0091 and Gold Creek. In all, ten tributary sites were selected for detailed sampling.

In addition, while the longitudinal profile did not indicate significant thermal refuge habitat in any pools, a site was added for sampling to have at least one representative sample. A pool located at approximately the Tolt River pipeline crossing was added based on results in Fresh et al. (1999) showing that it was used in 1998 by holding adult Chinook salmon.

3.3 DETAILED SITE TEMPERATURE FIELDS Sampling was strategic, where each site was visited 1-2 times to maximize the range of the flow and temperature data. The field data are reproduced in Appendix B. While the resulting data are not completely representative of extremely high temperatures at all sites, there was still good variation in the characteristic flows and temperatures within and across sites (Table 3-3). The variation appears to be sufficient for evaluating the implications of theoretical analyses and for developing a regression of habitat volume vs. the two key variables influencing thermal mixing zone size which are flow percentage contributed by a tributary and temperature difference between tributary and river; these subjects are addressed more thoroughly in Section 6. The basic temperature analysis results are presented below.

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0088 Relatively large tributary inflow observed Gold Creek (but in different location than on WDFW ≈0.1 Detailed measurement (Gold Creek) map); Prominent temperature drop observed Tributary inflow observed; No temperature Detailed measurement to add to na Derby Creek <<0.1 change observed sample size Tributary inflow observed; No temperature Detailed measurement to add to 0090? Unnamed tributary change observed; located further downstream <<0.1 sample size, sample same day as than shown on WDFW map Derby Creek Tributary inflow observed; No temperature change observed, but enhanced cool water Detailed measurement to add to 0091 Unnamed tributary mixing zone could conceivably extend to Not calculated sample size, sample same day as under NE 145th St bridge; Return visit Derby Creek indicated minor local cooling exists

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Table 3-2. Review of Sammamish River tributaries identified, their thermal influence, and recommendations for detailed temperature field sampling based on the results of the longitudinal temperature profile sampling and miscellaneous grab samples. Thermal WDFW Influence Mixing Recommendation Stream Code1 Site Name Comment Index (°C) Tzributary inflow observed; No temperature 0095 Unnamed tributary Not calculated Drop change observed Unmarked tributary on Tributary inflow observed; Recon visit from na right bank above NE trail indicated only 1°C temperature <<0.1 Drop 124th St bridge difference with Sammamish River No temperature change observed; did not 0099 Unnamed tributary Not calculated Drop see/hear tributary inflow No temperature change observed; did not 0100 Unnamed tributary Not calculated Drop see/hear tributary inflow Tributary inflow observed; no temperature 0101 Unnamed tributary <<0.1 Drop change observed Tributary inflow observed; no temperature 0102/0103 Unnamed tributary <<0.1 Drop change observed Tributary inflow observed; no temperature 0104 Peters Creek <<0.1 Drop change observed 0105 Bear Creek Temperature drop observed 1.2 Detailed measurements Did not find tributary 141; temperature drop 0141 Unnamed tributary observed on bottom but attributed to Not calculated Drop stratification of Lake Sammamish Tributary inflow observed; Temperature drop Detailed measurements because of 0142 Unnamed tributary observed over diffuse area in aquatic <<0.1 importance of location and vegetation observation of cooling influence

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3.3.1 Tributary Sites More than 90 sets of temperature contour plots were evaluated. After several iterations in Surfer to generate reasonable looking results, the final contour maps were exported to AutoCAD as DXF format files, and final temperature contour lines digitized to scale in AutoCAD using the Surfer-generated contour lines for temperature and bounding bathymetry. In a few instances, professional judgment was used to finalize the contour lines where the spatial distribution of data was more limited. The final bathymetry and temperature contour maps are presented in Appendix C. The area enclosed within each contour for each depth layer was calculated by AutoCAD for temperature increments of 1°C above the incoming tributary temperature, and the results are summarized in Table 3-4. Numbers are presented for those temperature increments where a closed contour could be clearly defined by the data. The data in the table should be considered to be order of magnitude correct given that a different gridding algorithm, and even modification of smoothing parameters specific to a given algorithm, would result in somewhat different placement of contour lines. In addition, the 2-D depth layer method that was applied could generate slightly different estimates of the 3-D temperature field if data had been collected at higher resolution depth intervals.

Swamp Creek is not presented in Table 3-4 because temperature fields in approximately the upper 3 ft of the water column and depths below about 5 ft were indicated in the contour plots to be under a strong thermal influence of Lake Washington. In the upper layer, there was no measurable influence of the tributary at the confluence that extended noticeably below the mouth. In the 3-5 ft depth layer, contours could be defined for temperatures +1°C, +2°C, and +3°C, but not for higher temperatures which exhibited a more chaotic temperature field representative of widespread and irregular mixing. Below 5 ft, temperatures rapidly approached a more uniform temperature in the 18.3°C to 18.9°C range, which appeared to reflect cooler temperatures in Lake Washington.

Despite the various limitations of the data, the numbers presented in Table 3-4 represent the general 3-D temperature fields occurring at each site, and can be used (i) to help rank sites for restoration (see Section 4) and (ii) for evaluating the potential benefits of augmenting tributary summer flows (see Section 6). The contours depicted in Appendix C are believed to provide reasonable representations of the 3-D temperature field at each site for the measured input flow and temperature conditions.

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3.3.2 Winery Pool Site No significant temperature stratification was found at this site. The largest difference measured between surface and bottom temperature was 0.2°C. A contour map generated using Surfer of the bottom layer temperature field indicated an area of approximately 87 ft2 enclosed by the 19.8°C contour, and a total area of 2260 ft2 at the bottom that was cooler than the ambient incoming temperature of 20°C.

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Table 3-3. Summary of site flow and temperature characteristics sampled for detailed temperature profile data in the Sammamish River, summer 2010 River Q Flow (cfs) from Gage Inflow Temperature (°C) (G) or ΔT° Measured % Flow From (River- Tributary Date Tributary Sammamish River (M) Tributary Tributary Sammamish River Trib) Swamp Creek 8/24/2010 6.15 79 G 7.22% 15.3 21.7 6.4 Horse Creek 8/13/2010 0.20 101 G 0.20% 16.7 21.0 4.3 8/5/2010 11.9 101 G 10.55% 18.6 22.6 4.0 North Creek 8/18/2010 13.3 100 M 11.76% 17.5 21.5 4.0 7/30/2010 8.31 151 M 5.21% 16.5 21.6 5.1 Little Bear Creek 8/17/2010 7.33 101 M 6.78% 17.4 22.4 5.0 Gold Creek 8/13/2010 2.43 77 G 3.06% 14.7 21.7 7.0 8/25/2010 2.88 57 M 4.81% 15.4 20.9 5.5 8/19/2010 NA 72 M na na 20.0 na Winery Pool 8/25/2010 NA 57 M na na 20.5 na 8/4/2010 0.06 95 G 0.06% 15.4 22.4 7.0 Derby Creek 8/25/2010 0.07 57 M 0.12% 14.3 20.3 6.0 8/4/2010 0.07 95 G 0.07% 15.4 22.4 7.0 Tributary 0090 8/25/2010 0.08 57 M 0.14% 14.0 20.5 6.5 8/4/2010 0.33 95 G 0.35% 17.2 21.8 4.6 Tributary 0091 8/25/2010 0.67 57 M 1.16% 16.7 20.1 3.4

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Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft. Area Contained Within Contour for Temperature Increase From Increase Smaller Than Specified, by Depth Layer Temperature Tributary (ft2) Total Sampling Contours Temperature Volume Tributary Date Analyzed (°C) (°C) Surface 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft (ft3) 17.7 1 5 3 Horse Creek 8/13/2010 18.7 2 52 26 19.7 3 178 89 19.6 1 340 331 413 764 696 637 63 3074 North Creek 8/5/2010 20.6 2 496 436 706 1209 1239 1488 168 5494 21.6 3 682 682 1194 1973 2451 2410 474 9525 18.5 1 372 347 441 801 1675 930 544 4924 North Creek 8/18/2010 19.5 2 456 430 904 1955 2408 2709 1334 9968 20.5 3 664 769 1646 2871 4933 5076 1394 17021 17.5 1 449 236 0 0 0 461 18.5 2 2213 1242 47 0 0 2396 Little Bear Creek 7/30/2010 19.5 3 4464 3833 497 0 0 6562 20.5 4 5837 4922 1572 0 0 9413

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Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft. Area Contained Within Contour for Temperature Increase From Increase Smaller Than Specified, by Depth Layer Temperature Tributary (ft2) Total Sampling Contours Temperature Volume Tributary Date Analyzed (°C) (°C) Surface 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft (ft3) 18.4 1 219 244 0 0 354 19.4 2 404 363 303 0 868 Little Bear Creek 8/17/2010 20.4 3 1605 770 441 0 2014 21.4 4 2338 1590 663 0 3422 15.7 1 94 0 0 0 0 47 16.7 2 305 4 0 0 0 157 17.7 3 427 91 0 0 6 311 Gold Creek 8/13/2010 18.7 4 529 225 20 43 163 716 19.7 5 652 372 102 179 314 1293 20.7 6 1070 770 525 612 789 3231 16.4 1 168 20 0 0 0 104 17.4 2 438 203 0 0 0 422 Gold Creek 8/25/2010 18.4 3 720 497 126 39 0 1022 19.4 4 1885 1601 767 950 199 4460

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Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft. Area Contained Within Contour for Temperature Increase From Increase Smaller Than Specified, by Depth Layer Temperature Tributary (ft2) Total Sampling Contours Temperature Volume Tributary Date Analyzed (°C) (°C) Surface 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft (ft3) 16.4 1 0 0 0 0 0 0 17.4 2 0 0 0 0 0 0 18.4 3 0 0 0 0 0 0 Derby Creek 8/4/2010 19.4 4 0 0 0 0 0 0 20.4 5 0 0 0 0 0 0 21.4 6 0 0 0 0 1 1 15.3 1 2 0 0 0 0 1 16.3 2 3 0 0 0 0 2 17.3 3 4 0 0 0 0 2 Derby Creek 8/25/2010 18.3 4 5 1 0 0 0 4 19.3 5 6 2 9 3 0 17 20.3 6 9 18 29 14 0 66

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Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft. Area Contained Within Contour for Temperature Increase From Increase Smaller Than Specified, by Depth Layer Temperature Tributary (ft2) Total Sampling Contours Temperature Volume Tributary Date Analyzed (°C) (°C) Surface 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft (ft3) 16.4 1 0 0 0 0 0 0 0 17.4 2 0 0 0 0 0 0 0 18.4 3 0 0 0 0 0 0 0 Tributary 0090 8/4/2010 19.4 4 0 0 0 0 1 0 1 20.4 5 0 0 5 0 14 0 19 21.4 6 0 0 23 0 38 0 61 15.0 1 0 0 0 0 0 0 16.0 2 0 0 0 0 0 0 17.0 3 0 0 0 0 0 0 Tributary 0090 8/25/2010 18.0 4 0 0 0 0 0 0 19.0 5 0 0 0 0 0 0 20.0 6 0 2 19 41 0 62 18.2 1 0 3 0 0 0 0 3 19.2 2 12 11 0 0 0 0 17 Tributary 0091 8/4/2010 20.2 3 28 29 0 0 0 0 43 21.2 4 88 81 7 3 34 0 169

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Table 3-4. Areas bounded by temperature contours for each depth layer sampled at the detailed temperature profile measurement sites in the Sammamish River in July and August 2010. The total estimated volume bounded by each temperature level equals the sum of the products of area times thickness of the layer, where the surface layer thickness is 0.5 ft and the others are 1 ft. Area Contained Within Contour for Temperature Increase From Increase Smaller Than Specified, by Depth Layer Temperature Tributary (ft2) Total Sampling Contours Temperature Volume Tributary Date Analyzed (°C) (°C) Surface 1 ft 2 ft 3 ft 4 ft 5 ft 6 ft (ft3) 17.7 1 16 21 4 12 0 0 45 Tributary 0091 8/25/2010 18.7 2 41 60 16 48 10 0 155 19.7 3 218 270 117 134 192 8 830 18.8 1 427 364 453 170 56 0 1257 Bear Creek 7/29/2010 19.8 2 535 571 802 560 263 52 2516 20.8 3 650 1144 1971 910 668 106 5124 20.5 1 927 872 482 342 121 0 2281 21.5 2 1349 1219 821 566 260 4 3545 Bear Creek 8/16/2010 22.5 3 3858 3710 2969 2448 680 6 11742 23.5 4 6732 6670 6123 5949 3175 17 25300 17 1 0 0 0 18 2 0 3 3 Tributary 0142 8/11/2010 19 3 54 7 34 20 4 69 22 57 21 5 89 61 106

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4. RANKING/PRIORITIZATION OF SITES FOR HABITAT IMPROVEMENT PROJECTS

The sites sampled during July and August 2010 (see Figure 2-4 and Appendix A for site locations and area of detailed temperature data collection, respectively) were compared and ranked in terms of feasibility and potential benefits to adult Chinook salmon. Criteria for evaluation and ranking included potential volume of thermal refuge habitat (where measured), contribution of flow by the tributary relative to the Sammamish River flow rate, temperature differences during warmer periods between the inflow and receiving water, site physical characteristics, site constraints influencing constructability and cost, relative contribution of sediment influencing project function and longevity, factors influencing longer term pool maintenance, presence of instream cover and riparian shading, public safety, and other factors. These various elements influencing overall ranking and suitability for constructing a temperature habitat modification project are described below for each site. At the end of this section, the various criteria are ranked in Table 4.1, from which five sites are identified as having greatest potential for improving temperature refuge habitat in the Sammamish River. Conceptual structural measures for each of the five sites are then described in Section 5.

4.1 SWAMP CREEK Swamp Creek is the third largest tributary to the Sammamish River in terms of summer flows and has a clear thermal moderating influence. The mouth appears to be a staging area for adult Chinook salmon migrating up the Sammamish River (K. Fresh NMFS and E. Warner MITFD, unpublished data). In addition, what may have been land-locked sockeye or kokanee salmon (O. nerka) based on size, color and date were observed breaching all day at the confluence while detailed temperature profile data were collected. However, there are seven key factors that adversely influence the feasibility of this site for structural modifications:

The confluence appears to be strongly influenced by the thermocline from Lake Washington, as seen in our data and in the study by DeGasperi (2009), which could inhibit the potential influence and benefits of structural measures.

The river is deepest at this site compared with upstream, which would influence design and construction cost.

The confluence is adjacent to a private residence where a resident did not appear to be receptive to our presence during data collection and presented a somewhat hostile working environment.

The general vicinity of the confluence experiences the heaviest recreational power boating traffic of all the sites.

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There is no effective riparian vegetation present and little opportunity for restoration because of the width of the Sammamish River limiting the influence of trees lining the south bank and most of the north bank is private residential property.

Swamp Creek backwaters during the summer up to about 100 ft downstream of the NE 175th Street bridge, and thus the mixing influence may extend an undefined distance upstream in the backwater area.

4.2 HORSE CREEK (TRIBUTARY 0068) Horse Creek flows through Wayne Golf Course before discharging into the Sammamish River. There is accordingly little shading available in the lower reach of the tributary and this may reduce the potential utility of this stream as a cooling source. The detailed temperature profile sampling indicates a relatively small region of cooling habitat present relative to the cross- section profile of the river. The following five factors may influence potential benefits of expanding temperature refuge habitat in the Sammamish River:

The area of cooling influence is confined to near the edge of the river and is generally shallow; suitability of this site depends to an unknown extent on whether adult Chinook salmon would use this shallow, exposed habitat or be more likely to key in on depth cover and stratification near the riverbed.

This reach of the Sammamish River experiences heavy recreational power boating traffic.

The river is still relatively deep at this site compared with upstream, which would influence design and construction cost.

Construction access would have to be through the golf course, which would likely require expensive mitigation for potential interference with use of the course.

Horse Creek is located near the downstream end of the Sammamish River and thus is not as critical a location for fish that migrate up the length of the river compared with upstream sites in terms of cumulative exposure to elevated temperatures.

4.3 NORTH CREEK North Creek was the subject of a detailed analysis of temperature refuge habitat potential performed by R2 (2009a,b) for the City of Bothell. Three alternatives were identified by R2, and one was determined to be feasible and was taken to the 30% design level. The selected alternative involved installing logs that help separate confluent flows from the river and tributary, thereby retarding mixing in the river and extending the plume downstream. The tributary contributes a significant amount of cooling flow that is protected upstream by the UW Bothell-Cascadia Co-Located Campus stream and floodplain restoration project. North Creek provides thermal refuge habitat roughly a quarter of the way upstream to Lake Sammamish. The

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confluence is located on the outside of a sharp bend in the river thus a pool is maintained hydraulically by high flows where the river appears competent to transport bedload exiting North Creek downstream through the potential refuge habitat area. However, the following two factors may influence potential benefits of expanding temperature refuge habitat in the Sammamish River:

The site is located at approximately the upstream extent of recreational power boat traffic, and the structural measure selected and designed to the 30% level by R2 was located in sufficiently shallow water during the summer that a risk exists of damage to boats piloted by unaware or less careful boaters.

North Creek experiences adverse water quality impacts from urbanization, with potential pollutants draining to the stream as stormwater runoff or through spills (accidental or otherwise) potentially affecting low flow water quality (e.g., Snohomish County 2000).

4.4 LITTLE BEAR CREEK Little Bear Creek is the smallest of the four significant tributaries to the Sammamish River, and is located approximately 1 mile upstream of North Creek. The confluence therefore may provide an alternative thermal refuge location for upstream migrants complementary with North Creek being nearby. As a tributary it provides a significant cooling influence as evidenced in the temperature profile data. The banks are lined with larger trees providing shade and construction access is good. The following four factors may influence feasibility of expanding temperature refuge habitat in the Sammamish River, however:

Little Bear Creek discharges a large volume of bedload composed of small gravel that deposits at and below the mouth along the right bank (Figure 4-1). The deposit forms an extended shallow cool water refuge habitat area that has limited utility to holding adult salmon because of their exposure to predators and anthropogenic interference. It is likely that any structure built at this location along the left bank to create deeper cool water habitat would fill in a few years with bedload. Design of a self-maintaining pool-creating structure would require more extensive analysis and potentially physical modeling.

The quality and quantity of gravel and small cobble present in the river at this location appears to be highly suitable for spawning. We observed the riffle that is likely formed in large part by bedload from Little Bear Creek to be used heavily by spawning sockeye salmon (O. nerka) during fall 2010, and structural measures to extend the thermal refuge habitat would likely require re-grading this deposit with potential adverse effects to spawning habitat availability.

The site is used heavily by recreational swimmers because of ready access to the Burke Gilman Trail and location within the limits of downtown Woodinville. While swimmers

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would likely stick to the warmer pool immediately upstream of the confluence, it is possible they would disturb and scare off adult Chinook salmon holding downstream.

Little Bear Creek experiences adverse water quality impacts from urbanization, with potential pollutants draining to the stream as stormwater runoff or through spills (accidental or otherwise) potentially affecting low flow water quality (e.g., Snohomish County 2000).

Figure 4-1. Bedload deposit along right bank of Sammamish River at the Little Bear Creek confluence. Photo was taken standing in Little Bear Creek.

4.5 GOLD CREEK (TRIBUTARY 0088) Gold Creek is the only mid-sized tributary with flow magnitudes intermediate to the four primary (Swamp, North, Little Bear, and Bear creeks) and the other much smaller tributaries. It is lined with trees as it flows over the Sammamish River floodplain and provides some of the coolest influent water of all the tributaries. This may reflect the strong groundwater hydraulic gradient found in this reach by Carey (2003). The thermal mixing zone is substantially larger than the other small tributaries based on the detailed temperature profile data. Public access to the river from the adjacent Burke Gilman Trail is restricted by a bridge railing/fence and riparian vegetation, but construction access is otherwise good from either bank. The Tolt River pipeline is located far enough upstream to not be a concern for damage from construction equipment.

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Riparian shading of the river is moderate. The tributary confluence is located roughly half-way between Lake Washington and Lake Sammamish and appears to provide the most thermal refuge habitat between Little Bear and Bear creeks for adult Chinook salmon. The site therefore may be critical to providing a strategically located respite from cumulative exposure to elevated temperatures over the migration route. The only potential factor influencing potential benefits of expanding temperature refuge habitat in the Sammamish River is that recreational paddlers use this reach of the river, however, there is little incentive for them to remain onsite for long and thus disturbance to holding fish would not be expected to change substantially with a project in place. In addition, the temperature volume-tributary inflow analysis suggests that this site could also potentially benefit from flow augmentation (see Section 6). This site appears to hold greatest potential for a meaningful, incremental thermal refuge habitat benefit out of all the smaller sites.

4.6 WINERY POOL AT TOLT PIPELINE This site was missed during the initial longitudinal profile because of its small size and the absence of significant temperature stratification in 2010. It was selected as a detailed temperature profile sample site because adult Chinook were recorded to hold at this location in 1998 during the NMFS-WDFW-MITFD radio-tracking study (K. Fresh, E. Warner, unpublished data), and. A negligible temperature difference was recorded between the surface and bottom (0.2°C) on both occasions sampled in 2010. It is unclear if this is because 2010 was generally a cooler summer compared with other years, or if there is another reason. In addition to the uncertainty over the extent of temperature stratification, this site has two other potential drawbacks:

The pool is located in very close proximity to the City of Seattle‟s Tolt River water supply pipeline which crosses underneath the Sammamish River. The pool is maintained by bend scour processes, thus it would be possible to design a structure that induces greater scouring, but it is uncertain if this would increase risk to the pipeline. In addition, some additional bank toe protection work would likely be required along the outside of the bend to prevent erosion during high flows. Design and construction costs are expected to be higher than for most other sites.

Recreational paddlers use this reach of the river and there is a rudimentary private canoe and kayak launch in the vicinity on the left bank. It is thus possible that paddlers entering and leaving the water here might disturb holding fish.

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4.7 DERBY CREEK AND TRIBUTARY 0090 Derby Creek is located approximately 100 ft downstream of Tributary 0090 on the same (right) bank. Both drain to the Sammamish River through perched culverts and contribute a negligible amount of flow during the summer. The upstream of the two was named Tributary 0090 in this study because it is closer to the location of the so-numbered channel depicted approximately 1000 ft upstream in the Washington stream catalog (Williams et al. 1975). Without researching the development history more thoroughly, it is assumed that the original channel depicted in Williams et al. (1975) may have drained two sources that were later re-routed to two outfalls farther downstream with construction of the recreational ball fields on the right bank floodplain. In any case, the following three factors may influence potential benefits of expanding temperature refuge habitat in the Sammamish River:

While their temperatures were measured to be considerably cooler than in the river, the thermal influence of these two streams is negligible because of their small flow magnitudes and the perched nature of the culverts facilitating partial warming of the water before it reaches the river.

There is little to no riparian shade present currently.

Both sites are readily accessible from the trail, making them potentially susceptible to disturbance.

4.8 TRIBUTARY 0091 The amount of flow measured in August 2010 was relatively high compared with the other small tributaries draining the floodplain, and the detailed temperature profile data indicate the existence of a larger mixing zone than most other small tributaries except for Gold Creek. It is possible that this tributary intercepts groundwater drainage from the west side of the Sammamish River valley as its channel runs along the base of NE 145th Street where the road prism may pose a less permeable drainage path. The tributary is located at the upper end of a reach with a strong down-valley groundwater hydraulic gradient (Carey 2003). Importantly, the mixing zone extends under the bridge which provides overhead shading, and the side of the channel affected is generally inaccessible to the public. Next to Gold Creek, therefore, this site appears to hold greatest potential for a meaningful, incremental habitat benefit out of all the remaining smaller sites. There is a single major factor adversely influencing the feasibility of expanding temperature refuge habitat in the Sammamish River by structural means, however:

The site is located underneath the NE 145th Street bridge, which rests on pilings embedded into the riverbed within the zone of thermal influence of Tributary 0091 (Figure 4-2). Design requirements would be more expensive than for most other sites,

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and it might be more difficult to meet a no-rise criterion here because of the pilings. The site would, however, be a highly suitable mitigation project should the bridge be replaced in the future by a full spanning structure and the pilings were removed.

Figure 4-2. Bridge pilings under NE 145th Street bridge. Tributary 0091 enters at the left edge of the photograph. Photo was taken December 2010 demonstrating influence of pilings on flow.

4.9 OUTLET OF CONSTRUCTED WETLANDS AT NE 124TH ST/HOLLYWOOD PUMP STATION This tributary was not identified in the stream catalog (Williams et al. 1975). It drains a constructed wetland complex than runs along the south side of NE 124th Street from the east, which in principle should represent a suitable water source. There is limited shading from riparian vegetation, but the NE 124th Street provides overhead shade about 120 ft downstream of the confluence. Flows were measurable during the summer, but there are two factors adversely influencing the feasibility of expanding temperature refuge habitat in the Sammamish River:

The temperature of the tributary was measured to be only 1°C cooler than the Sammamish River. This likely reflects the presence of beaver, which reportedly have cut

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much of the shade vegetation planted upstream in the wetlands complex and created dams backing up the water (Roger Dane, City of Redmond, 2010 personal communication to P. DeVries). The resulting impoundments appear to be warming the water. This site was consequently not selected for more detailed temperature profile sampling

There is a large deposit of fine sediment at the mouth. It is suspected but unconfirmed that much of the material this may have originated from the tributary, in which case this could affect the design of a structure creating suitable scouring conditions needed to maintain a sufficiently deep cool water area at the confluence.

4.10 TRIBUTARY 0101 Tributary 101 contributes relatively little flow during the summer and has a negligible influence on thermal conditions in the Sammamish River. Although the measured water temperature was relatively cool compared with other sites, the stream flows out of a perched culvert, facilitating partial warming of the water before it reaches the river. It was not considered for detailed temperature profile sampling because of these factors, and because Derby Creek and Tributary 0090 were considered sufficiently representative.

4.11 TRIBUTARY 0102 Tributary 102 contributes the least amount of flow during the summer out of all the tributaries surveyed. It has a negligible influence on thermal conditions in the Sammamish River and was thus not considered for detailed temperature profile sampling.

4.12 PETERS CREEK (TRIBUTARY 0104) Peters Creek has undergone extensive habitat restoration by the City of Redmond, and the restored riparian vegetation has grown sufficiently that the water remains relatively cool when it reaches the Sammamish River. The tributary mouth is relatively wide and could provide a small amount of thermal refuge habitat space. Water temperatures are relatively cool and summer flow rate is comparable to the other smaller tributaries. There is one factor adversely influencing the feasibility of expanding temperature refuge habitat in the Sammamish River by structural means, however:

There is a series of three concrete weirs that are variously submerged at different flow rates in the Sammamish River. The lowermost weir is recessed from the main channel and is nearly completely submerged during the summer, but it generally prevents significant mixing with the Sammamish River. Most mixing occurs within the footprint of the weirs, where the temperature difference between the downstream side of the middle weir and the confluence with the Sammamish River was measured to be only

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0.5°C in late July 2010. The concrete weirs appear to provide upstream grade control and passage to coho salmon and cutthroat trout, where their modification to increase thermal refuge habitat may conflict with fish passage goals. This would need to be factored into a design, and would likely require working closely with the City of Redmond.

4.13 BEAR CREEK Bear Creek is the largest cool water source to the Sammamish River and is critically located near the upper end of the Sammamish River for fish migrating through Lake Sammamish. It is also an important spawning and rearing stream, with a significant cool water source originating in the Cottage Lake Creek basin. Adult Chinook salmon regularly hold below the mouth of Bear Creek in the thermal mixing zone (E. Warner, MITFD, 2010 personal communication to P. DeVries). While the bathymetry data collected as part of the detailed temperature profile sampling effort indicate the existence of a sediment deposit along the right bank at the confluence and downstream, the water is sufficiently deep to be usable by holding adults. In contrast to the confluence with Little Bear Creek, the Sammamish River appears competent to transport bedload originating from Bear Creek with the current bathymetry representing what appears to be an equilibrium condition. There is no ready public access but construction access would be possible from the SR 520 expansion project site. Mature trees growing along the left bank separate the river from the public trail and provide significant shading. The thermal mixing zone is among the largest in the river.

This site potentially represents a good opportunity for creating additional thermal refuge habitat, but there are two factors presently influencing feasibility of developing structural alternatives for expanding temperature refuge habitat in the Sammamish River as part of this study:

The City of Redmond has completed 60% designs and is presently applying for permits to move the mouth of Bear Creek approximately 100 ft downstream as part of its larger restoration project in Bear Creek. It is proposed that the existing Bear Creek channel be maintained as a backwater extending upstream for about 260 ft and filled upstream of there. While the proposed orientation and topology of the new confluence on the design drawings (provided by R. Dane, City of Redmond) would be very similar to the existing confluence, it is uncertain if the hydraulics and bathymetry would end up similar to the existing confluence location. The left bank of the Sammamish River protrudes slightly at the current confluence, and may partially direct high flow streamlines towards the right bank (Figure 4-3). This flow redirection, while likely not pronounced, combined with large flood flow rate in Bear Creek and the general shape of the confluence, may facilitate more efficient transport of bedload than if the left bank were straighter as is the case at the location of the proposed new confluence. Thus, it is not possible to develop a

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thermal refuge habitat design for the Bear Creek site until the City of Redmond project is completed and the effect on bedload transport and deposition at the new confluence is understood. Indeed, it would be beneficial if the final design for that project also incorporated measures to increase the thermal refuge zone in the Sammamish River.

Water temperatures measured at the mouth of Bear Creek during the detailed temperature profile data collection efforts were warmer than expected (Table 3-3). A review of King County gage data indicates that warming occurred between the Union Hill Road gage and the mouth, on the order of +1.5°C on July 29, 2010, and +1.6°C on August 16, 2010. Conversely, relatively little warming occurred between the Union Hill Road gage and the 133rd St NE gage located farther upstream (+0.1°C and +0.6°C, respectively). The reason for this increased warming below Union Hill Road and the mouth was not investigated as part of this study. Historic temperature measurements made by King County do not extend sufficiently back in time to evaluate whether this may be related to restoration efforts completed in Bear Creek ca. 1999 (www.redmond.gov/common/pages/UserFile. aspx?fileId=22753). Available data suggest mean upstream-downstream increases in mean daily temperature between the gages located at Union Hill Road and the mouth may be larger after 1999, but the mean increases in maximum daily temperatures do not indicate a similar potential trend (Figure 4-4). Additional work appears needed to determine if the changes are real and whether this would reduce the effectiveness of a structural project to increase thermal refuge habitat below the mouth of Bear Creek. Growth of restored riparian vegetation would be expected to reduce the potential for temperature increases in the lower reach of Bear Creek over the long term, when constructing a temperature refuge habitat project may be more effective.

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Figure 4-3. Confluence of the Sammamish River and Bear Creek. Note the convex portion of left bank that may deflect higher flows partially towards the right bank below the mouth during high flow, as suggested by the left arrow. The larger flood flows in Bear Creek and the confluence geometry also appear to work against excessive deposition at the mouth (as seen for example at the confluence with Little Bear Creek; Figure 4-2).

4.14 TRIBUTARY 0142 The reach of river between Bear Creek and the weir at the outlet of Lake Sammamish is generally warmer than downstream and there appears to be little thermal refuge habitat available (Fresh et al. 1999). Tributary 0142 is located upstream of the weir controlling outflow from Lake Sammamish and while its outflow appears to be small in magnitude, it appears to be associated with a diffuse thermal refuge area among lily pads near the left bank that may reflect groundwater inputs as well. The bottom is extremely muddy, however, which could affect constructability and function of a structural measure. Velocities are negligible and the cool water area is relatively shallow, thus it is possible that once adult Chinook salmon have passed over the weir they could be influenced by a slight thermal stratification (e.g., Figure 3-3) and migrate to deeper water in Lake Sammamish, and not find the cooler peripheral habitat. This site was therefore not considered for more detailed temperature profile sampling.

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1.2

C) ° 1.0 July - Average July - Daily Max August - Average 0.8 August - Daily Max

0.6

0.4

0.2

0.0

TemperatureDifferencebetweenGages ( Rd HillMouth and Union 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

-0.2

Figure 4-4. Mean increases in (i) mean daily and (ii) maximum daily water temperatures between King County gages located in Bear Creek at Union Hill Road and the mouth, for the months of July and August over the period of record. Missing data indicate incomplete record.

4.15 THE FIVE HIGHEST PRIORITY SITES WITH GREATEST POTENTIAL TO BENEFIT CHINOOK SALMON HABITAT THROUGH INCREASED THERMAL REFUGE HABITAT VOLUME In general, our assessment indicates that there is no single ideal site with all factors favoring creation of extensive, important thermal refuge habitat. However, it is possible to identify sites where conditions overall are such that biologically meaningful thermal habitat refuge may be expanded through structural means or by flow increases, subject to the caveats noted above. Based on features described above, the following factors were evaluated and ranked for each site:

Thermal Influence on River: An interpretation of the results reported in Table 3-4, where sites with greater volumes of thermal mixing are given a higher ranking.

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Potential for Incremental Benefits of Thermal Habitat Enhancement: Sites with flows nearer the threshold for significantly increasing the volume of the mixing zone based on the ratio of tributary flow rate to Sammamish River flow rate are ranked highest. Sites with little to no flow are ranked lowest.

Strategic Value of Location in River Network: Sites in the upper half of the river below the weir at the outlet of Lake Sammamish River are ranked the highest because of the increased cumulative effect of exposure to elevated water temperatures as adult Chinook salmon migrate upstream. Adding more thermal refuge habitat in the upstream half would help reduce cumulative adverse effects nearer the end of their migration through the river.

Conflicting Management Actions/Infrastructure: Sites with no infrastructure potentially affected by a project, or are not affected by known city or county management plans are ranked highest. Sites where infrastructure considerations require the greatest level of engineering design, permitting, and multiple stakeholder involvement are ranked lowest.

Public Access/Safety Impacts: Sites where construction or presence of a project may pose as an attractive nuisance or could directly affect public safety are ranked lower.

Constructability: Sites where construction methods or design are perceived to require more extensive design work, and thus increase likely cost, are ranked lower.

Tributary Bedload Impacts: Sites with negligible bedload delivery to the river are ranked higher because design requirements are less and the likelihood of project functioning as intended is higher.

Existing Shading (Riparian, Constructed): Sites with midday to afternoon shading already reducing solar insolation to the stream are ranked higher.

The rankings for each factor are summarized in Table 4-1 and were used to help identify five sites for which thermal refuge habitat restoration projects would likely provide greatest potential benefits to adult Chinook salmon. The ratings given in the table are somewhat subjective, but to the extent possible reflect the following general system that appears to result in overall rankings that make sense based on the data collected and observations made during this study:

1 = Higher ranking (most feasible/highest potential benefit) 2 = Moderate ranking (still feasible or with potential benefit, but secondary in nature) 3 = Lower ranking (features exist that mat adversely affect feasibility/benefits/design) 6 = Potentially significant problem exists that would likely adversely affect feasibility

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The ratings were summed across columns in Table 4 to yield a net rating that was itself ranked. Based on the collective rankings listed in Table 4-1, the following five sites were identified and prioritized in order from highest to lowest:

1. Gold Creek 2. Bear Creek 3. Tributary 0091 4. North Creek 5. Little Bear Creek Most other sites do not appear to be good candidates because of the small flow contribution and minor thermal influence of the smaller tributaries, or factors influencing constructability or general feasibility.

Of the five, Gold Creek appears to be the best candidate site to take forward to design and construction at this point in time for several reasons:

Good summer flow with low temperatures, resulting in a relatively large thermal mixing zone that could be expanded measurably with relatively inexpensive structural measures and/or flow augmentation;

Strategic location along the length of the Sammamish River for holding Chinook Salmon (near the midpoint, providing thermal refuge in the long stretch between Little Bear and Bear creeks);

Accessibility and constructability; and

No conflicting infrastructure.

The mouth of Bear Creek is another good site because it has the most contributing flow of all the tributaries, but uncertainty over future bathymetric and temperature conditions at the mouth preclude developing a design at this point in time.

The Tributary 0191 site is a good candidate for flow augmentation now, and designing and constructing an instream structure later when the NE 145th Street bridge is replaced. It has a relatively large flow rate and thermal influence for a small tributary, and the bridge provides shade cover. It is in a similar location as Gold Creek for upstream migrants, approximately midway between Lake Washington and Lake Sammamish.

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The North Creek site has already been demonstrated to be a good candidate for a thermal refuge habitat restoration project because of its relatively large summer flow rate and bathymetric properties, and a candidate design has been developed previously (R2 2009a,b). However, there are complications associated with recreational power boat use that would likely require more iterations in the design and stakeholder involvement process. In addition, the reach downstream exhibits greater vertical temperature stratification than upstream, potentially providing more distributed (albeit diffuse) thermal refuge habitat.

The Little Bear Creek site has a relatively large thermal refuge area but much of it is effectively unusable because it is shallow, and bedload transport-associated problems and public accessibility may be overriding concerns. A more detailed study appears necessary to further evaluate the potential for expanding thermal refuge habitat area at the site in a sustainable way without adversely affecting salmon spawning habitat in the river.

These five sites are the subject of the Section 5 in which conceptual designs are identified and the final design selected for the Gold Creek site is described.

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Table 4-1. Results of ranking candidate thermal refuge habitat enhancement sites by factors influencing feasibility and potential benefits, and overall ranking for prioritization. Highlighted cells denote highest ranking sites for each factor. A lower magnitude denotes higher ranking. See text for explanation. Range of Potential for Public Measured Input Incremental Strategic Conflicting Access Flow Thermal Benefits of Value of Management / Existing Tributary/Site Percentages Influenc Thermal Location Actions/ Safety Tributary Shading Sum of (Trib/ e on Habitat in River Infrastructur Impact Construc Bedload (Riparian, Factor Overall Mainstem) River Enhancement Network e s t-ability Impacts Constructed) Rankings Rank Swamp Creek 9.4% 3 3 3 3 3 3 2 3 23 10 Horse Creek 0.17%-0.25% 6 6 3 6 3 3 1 3 31 12 North Creek 11%-12% 1 2 2 1 3 3 2 3 17 4 Little Bear 5.2%-7.2% Creek 1 2 2 1 3 1 6 1 17 5 Gold Creek 2.8-4.7% 2 1 1 1 2 1 1 2 11 1 Winery Pool na 6 6 1 6 2 3 1 2 27 11 Derby Creek 0.06%-0.12% 6 6 1 1 2 1 1 3 21 8 Tributary 0090 0.06%-0.13% 6 6 1 1 2 1 1 3 21 8 Tributary 0091 0.35%-1.2% 2 1 1 6 2 3 1 1 17 3 Wetland Outlet @ NE 124th 0.34% 6 6 1 2 2 1 2 3 23 10 Trib 0101 0.24% 6 6 1 1 2 1 1 3 21 8 Trib 0102 0.01% 6 6 1 1 2 1 1 2 20 7 Peter's Creek 0.24% 6 6 1 2 2 2 1 2 22 9 Bear Creek 17%-23% 1 2 1 6 1 1 3 1 16 2 Tributary 0142 Not Measurable 3 3 3 1 1 3 1 3 18 6

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5. POSSIBLE STRUCTURAL MEASURES FOR IMPROVING THERMAL REFUGE HABITAT IN THE SAMMAMISH RIVER

This section first presents conceptual designs and planning level cost estimates for structural alternatives in the five sites where biologically meaningful expansion of thermal refuge habitat may be most productive. One alternative is then selected for the Gold Creek site, which based on the ranking and prioritization review presented in Section 4, appears to provide the best opportunity currently. The design and associated analyses for that site and alternative are then described. The resulting design is “final” in the sense that construction and performance details of the structure have been worked out for an alternative that is feasible and constructible. However, as will be made evident below, the available grant budget for this work is insufficient for completing the design pending unknown final permitting needs, and thus the design presented here may be considered final in the context of initiating permitting. In addition, it was assumed during scoping that geotechnical engineering would not be needed as part of the design. Additional funds may be necessary for fine-tuning the design, and we identify below the remaining aspects of the design requiring finalization.

5.1 CONCEPTUAL DESIGNS FOR THE FIVE HIGHEST PRIORITY SITES There are three general structural options that appear feasible in the Sammamish River for improving temperature refuge habitat availability, with variations tailored to each of the five tributary confluences considered for conceptual design:

Option 1 Installation of instream western red cedar or Douglas fir log and/or rock structures that help route Sammamish River streamlines away from the mixing zone, thereby creating a more sheltered area at low flow that results in retarding mixing and prolonging the downstream extent of the thermal plume. Logs would be expected to last more than 50 years if fully submerged (e.g., Murphy and Koski 1989). This option would require addition of a cobble-gravel scour protection apron on both sides of the logs, and sculpting of cobble and gravel added near the bank on the upstream side of the log structure to create more hydraulically efficient, converging streamlines that reduce the roughness effect of the structure on the 100 year flood level.

Option 2 – Modifying channel planform:

In straight reaches (i.e., Gold Creek, Tributary 0091, Bear Creek), creating a gentle meandering planform where the confluence is located at a constructed bend and geomorphic processes promote pool formation and maintenance. This would involve

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placing fill material to construct gravel-cobble bar forms on the opposing bank upstream and downstream of the confluence, with a wavelength between bar apices equal to roughly 5-7 channel widths following general geomorphic criteria (e.g., Leopold et al. 1995). A compensatory excavation of the banks would be required to meet the no-rise criterion. This option has already been implemented more generally below Bear Creek by the City of Redmond to create habitat diversity.

In existing curved reaches where the tributary is located on the outside of a bend, work with bend scour processes to either create more of a quiet zone in which the cool water can sit for longer (i.e., North Creek) or concentrate flow closer to the confluence mouth to maintain bend scour (i.e., Little Bear Creek). The designs would need to include measures preventing bedload transport from refilling the thermal refuge habitat area and causing shallower water that would eventually be unusable for adult Chinook salmon with sufficient fill.

Option 3 A combination of the above, which could involve scaling back or modifying the extent to which Options 1 and 2 would be implemented (e.g., reduce instream structure size, and extent of channel relocation and/or fill) to varying extents depending on site and final design criteria and constraints

All alternatives would benefit from increased shading by tall riparian trees in association with the project, with extent of benefit depending on the site. These structural measures are laid out together with general revegetation areas on scaled aerial photographs of each of the five highest priority sites in Appendix D, and planning level cost estimates are provided below. Constraints and permitting needs are identified that may affect cost and feasibility, and remaining design needs are identified.

In general, alternatives involving only instream structures would likely involve considerably less cost than modifying channel planform. The footprint of disturbance is less and the measures typically applied are relatively low in terms of cost and impact to design and build. Planform modification could require more detailed geotechnical sampling and design, more rigorous analysis of effects on flooding and levee status, and greater consideration of utilities and public right of way. Estimated costs for the City of Redmond‟s HEP IV project, which involves similar actions to increase channel sinuosity and complexity over a 1,200 ft long reach of the Sammamish River between NE 85th Street and the railroad trestle upstream were $2.3 million for full design, permitting, construction, invasive vegetation replacement, and contingency (Parametrix and R.W. Beck 2006).

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The above options were considered at each of the five sites. Appendix D contains scaled CAD drawings depicting Options 1 and 2 conceptually over aerial photographs. Where both Options 1 and 2 are feasible, Option 3 would by extension also be feasible. Planning level cost estimates are presented for Options 1 and 2 where feasible for each site in Table 5-1. Costs for Option 3 are expected to be between the cost for Option 2 and the sum of costs for both options.

Table 5-1. Summary of planning level cost estimates for constructing instream structures (Option 1) or channel planform modifications (Option 2) to create thermal refuge habitat at the five most promising sites identified in the Sammamish River. Site/Option Little Tributar Bear Gold Creek Bear Creek y 0091 North Creek Creek Item 1 2 1 2 1 1 2 2 Surveying, 100% Design 25,0001 210,000 35,0001 160,000 85,000 35,0001 70,000 65,000 Permitting 10,000 40,000 10,000 40,000 30,000 10,000 30,000 30,000 Mobilization, Site Preparation, Demobilizatio n 23,000 85,000 13,000 70,000 23,000 23,000 85,000 80,000 Erosion, Water Control 20,000 45,000 20,000 40,000 20,000 20,000 45,000 40,000 Earthwork 8,600 519,800 8,000 478,900 3,600 3,100 18,100 17,900 Habitat Work 15,000 180,000 32,400 109,800 16,200 21,600 54,000 16,200 Landscaping 6,300 39,000 6,600 23,100 2,160 1,500 2,460 0 Total Design, 100,00 Permitting 35,000 250,000 45,000 200,000 115,000 45,000 0 95,000 Total, 204,56 154,10 Construction 72,900 868,800 80,000 721,800 64,960 69,200 0 0 20% Contingency 21,500 223,700 25,000 184,300 35,900 22,800 60,900 49,800 Total Cost 129,40 1,342,50 150,00 1,106,10 137,00 365,46 298,90 Before Tax 0 0 0 0 215,860 0 0 0 1 – For the designs depicted in Appendices E (Gold Creek site) and D (other sites), assumes limited design optimization modeling is required, minor earthwork to meet no rise criterion, no geotechnical sampling is required,

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and no additional analysis required to address permitting, easement, or property concerns. Geotechnical engineering would cost up to approximately $10,000 extra per site.

5.1.1 Gold Creek Both structural and channel planform modification measures appear feasible at the Gold Creek Site. The following respective options were identified:

Option 1 A log structure could be constructed to divide the flow just upstream of the mouth of Gold Creek, and create a partially shielded zone for the cool water plume with reduced inflow from upstream in the river. Streamlines in the Sammamish River would be redirected to the left bank side of the log structure, thereby extending the plume and retarding mixing. Access would be from the Burke Gilman Trail. The final design for this option in this report assumes no excavation and special measures for earthwork would be required.

Option 2 The opposing (left bank) borders a light industrial/office complex and much of the bank is covered with blackberries. A relatively long topographic depression runs upstream of the confluence along the left bank and is separated from the river by fill. This depression could conceivably be opened up to re-meander the river and direct flow towards a constructed bend at the confluence. However, the feature extends to just north of the Tolt River pipeline, which at worst could adversely influence feasibility or at best would require additional study and design work. In any case, this option would require additional detailed modeling of bend hydraulics and scour to optimize the design.

A number of key potential constraints to successful design, permitting, and construction are identified for Option 1 as part of the final design in Section 5.2.2.1. The following constraints apply additionally to Option 2:

The presence of the Tolt River pipeline requiring special protective measures and potential easements from City of Seattle.

Obtaining construction easements and permitting from King County to modify the levee and/or trail. A portion of the Burke Gilman Trail might need to be moved to the east downstream of Gold Creek.

Storm drain modifications may be necessary along one or both banks.

Unknown soil and geotechnical engineering conditions influencing design of channel stabilization measures.

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Not impacting and designing sufficient flood protection for the light industrial/office complexes situated on private property along the left bank. A boundary survey will be required to delineate private property as part of the 30% design process, and to determine the need for easements and mitigation.

5.1.2 Bear Creek Both structural and channel planform modification measures appear feasible at the Bear Creek Site. As noted in Section 4, a key constraint is that the City of Redmond is presently seeking permits to move the mouth of Bear Creek approximately 100 ft downstream (both options). Assuming the mouth stays where it is, the following respective options were identified:

Option 1 A log structure could be constructed to divide the flow just upstream of the mouth of Bear Creek, and create a partially shielded zone for the cool water plume with reduced inflow from upstream in the river. Because of the size of Bear Creek and the mixing zone at the mouth, a relatively large structure could be constructed to retard mixing over a large area. Design would involve multiple iterations to find an optimal configuration and length of structure. The conceptual design presented in Appendix D lays out logs approximately within the current thermal footprint, which would result in cooler temperatures overall in that area. Access would be from the SR 520 bridge expansion project site. Successful implementation of this option is uncertain if the mouth is reconstructed 100 ft downstream, because of the potential for unanticipated scouring or erosion of the constructed banks at the confluence, or increased deposition of bedload at the mouth depending on the final orientation of the Bear Creek channel and topography of the confluence.

Option 2 The right bank could be excavated into and a bend constructed along the opposing (left bank) to create a larger scour pool at the mouth where cool water from Bear Creek could concentrate in. This has been implemented successfully by the City of Redmond at other locations, although the design for the mouth at Bear Creek may require more extensive sinuosity than in the City projects in order to maintain a sufficiently large and deep scour pool. The orientation of Bear Creek streamlines entering the confluence area could potentially be optimized to increase pool scour at high flow. As for the Gold Creek site, this option would require additional detailed modeling of bend hydraulics and scour to optimize the design.

Possible key constraints to successful design, permitting, and construction include:

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The footprint of the expanded SR 520 bridge restricts the upstream starting point location for Option 2 excavation, and will influence the design of an optimal meander wavelength and amplitude if the mouth is not moved downstream (Option 2).

The bedload regime of Bear Creek would need to be studied and analyzed more fully as part of the design. It is possible that there will be a temporary interruption or reduction in bedload supply as the stream adjusts to a lower gradient in the restored reaches between the mouth and Redmond Way, which could influence stability of both options through unforeseen scour.

While it appears unlikely that there are utilities present at the site that would be affected by the project, there is private property adjoining the site on both sides of Bear Creek that could require providing additional flood protection or obtaining easements as part of Option 2 whether or not the City of Redmond project proceeds.

5.1.3 Tributary 0091 While relatively small in area currently, the cool water zone resulting from this project during the summer could conceivably be designed to be moderately larger in area with suitable shielding from the river, and would be mostly shaded and away from public interference, thus the potential benefit of increasing temperature refuge habitat availability could be substantive. Because of the proximity of the NE 145th Street bridge and attached utilities, and the confined footprint of the Burke Gilman trail adjacent to the channel, it does not appear advisable to consider Option 2 (modification of channel planform) at this site. Hence, the only feasible option appears to be Option 1, involving placement of an instream wood or rock structure. A 30 ft long log could be installed at an approximately 30° angle extending downstream from the bank to the upstream, left side bridge pier. Logs or rock could be placed between the piers to extend the cool water mixing zone. Another 30 ft log without a rootwad could be placed downstream to extend the zone farther. Logs would require anchoring. Removal of blackberry and planting of riparian shade trees would add overhead cover and shade to the short stretch between the tributary inflow and the upstream edge of the bridge.

It is likely that the hydraulic contraction associated with the bridge piers would work to transport through any sediments arriving from upstream through the enclosed left side during high flows, thus the benefits of the structure should be preserved for many years. There would not be temporary construction impacts to the Burke Gilman Trail because all construction access can be achieved from the left bank.

Possible key constraints to successful design, permitting, and construction include:

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The presence of the bridge piers and abutments (Figure 4-2) influencing the ability of the design to meet the no-rise criterion.

The potential for scour around the bridge piers would need to be evaluated and used to size placement depth of logs between the piers.

Some form of easement may be required from King County regarding work within the bridge footprint, with likely extensive analysis and study a condition for the easement.

Debris catching on the upstream log could influence conveyance through the bridge, with periodic maintenance being required in addition to maintenance currently required for the bridge piers. King County may choose not to bear these additional costs as part of bridge maintenance.

The riparian planting plan would need to consider the potential for blow-down or other reason for falling in, and trees subsequently racking on the bridge piers.

The cost estimate assumes no complications with obtaining an easement involving private property or additional permitting requirements.

5.1.4 North Creek Both structural and channel planform modification options were considered feasible as part of previous work by R2 (2009a):

Option 1 A log structure could be constructed that extends along the general edge of the current mixing zone, which is topographically controlled along its upstream side by a riverbed ridge extending from the right bank. A scour hole exists at the bend that reflects both bend scour processes and the angle of flow emanating from North Creek. The ridge and log structure combined would guide low flows from the Sammamish River above the confluence to remain in the left half of the channel, and reduce the volume of warmer water flowing over the top of the cool water plume from North Creek depicted in Figure 5-1. The structure could consist of raising the bottom topography via a thin ridge constructed of rock, or a fence constructed of wood debris anchored to the bottom. This option could be readily modeled by changing the river bed topography locally to represent the projection of the structure into the water column. This option was considered less expensive to construct than an alternative structural instream measure considered that involving installing rows of pilings in the streamwise direction on each side of the current pool, and involved less disturbance of the riverbed. It was identified as the preferred alternative, and was predicted by the 2-D modeling to potentially increase thermal refuge area modestly (Figure 1-12).

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Option 2 The cool water area within the existing scour hole at the bend could be expanded by excavating into the right bank immediately below the confluence. The 3-D flow and temperature field was found to be such that the cooler North Creek plume plunged under a warmer surface layer from the Sammamish River (Figure 5-1), which upon flowing towards the curved right bank was forced toward the bottom and downstream along the right bank. Extending the pool area could extend stratification and volume of the cooler water plume lying under the warmer overflow. An excavator could work from the left bank.

North Cr

Sammamish R

Figure 5-1. Conceptual representation of three-dimensional flow patterns occurring in the confluence zone during the summer low flow period, as suggested by vertical temperature profile data. Warmer Sammamish River water flows over a descending cooler plume from North Creek, resulting in the warmer water measurements recorded along the right bank (from R2 2009a).

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Access for both options would be from the right bank, either just upstream of the confluence or downstream from the end of Woodinville Drive/113th Avenue NE.

Possible key constraints to successful design, permitting, and construction include:

Impacts to power boats (Option 1).

Temporary impacts to the Burke Gilman trail (both options) and utility lines.

Confirmation may be required in the form of test wells that there is no aquifer present near the riverbed elevation that could potentially be intercepted by vertical piles, excavation into the bank, or other construction disturbance (both options).

The potential for bedload exiting North Creek to deposit along the right bank and reduce the additional thermal refuge habitat created under Option 2.

Potential for additional flood and bank erosion risk analyses to address private property concerns at the mobile home park on the left bank opposite the mouth.

5.1.5 Little Bear Creek The heavy gravel bedload originating from Little Bear Creek appears to preclude a feasible application of Option 1 by itself. The bedload regime of Little Bear Creek and the hydraulics at the confluence would need to be studied and analyzed more fully (including potentially developing a physical model) as part of any future design involving instream structures. Any structure placed to further isolate the cool water zone from the main river would likely fill with bedload behind it over the long term (or refill if a portion of the current riffle deposit is excavated). Option 2 could be feasible if it involves constructing a stable bar on the left bank along the inside of the bend, opposite the mouth of Little Bear Creek. Log structures could be placed along the leading upstream edge of the bar to help keep it in place and direct high flow streamlines toward the mouth of Little Bear Creek to help concentrate flow and flush incoming bedload downstream through a forced pool. The hydraulically formed pool would provide the majority of cool water habitat during the summer.

5.1.6 Permitting Requirements Permitting requirements would be less complicated for most instream structures, and with the exception of the Tributary 0091 site which involves integrating infrastructure into the design, could reasonably involve obtaining a streamlined Joint Aquatic Resource Project Application (JARPA), which includes a Hydraulic Project Approval (HPA) from WDFW, a Section 404 Nationwide Permit from the U.S. Army Corps of Engineers, and a 401 Water Quality Certification from Washington Department of Ecology (DOE). This would generally bypass

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State Environmental Policy Act (SEPA) checklist, Coastal Zone Management Program Certification, and local shoreline management permit requirements. Because of the extensive disturbance involved, a channel planform modification project would likely be permitted under a standard JARPA and thus would not qualify for exemption from other state and local permit requirements. Cultural resources assessment requirements would also likely be required and would be more restrictive for a channel planform modification project (e.g., Northwest Archaeological Associates 2006).

5.2 FINAL DESIGN FOR THE GOLD CREEK SITE As indicated in Section 4, the Gold Creek site appears to be the best site at this time to implement a structural measure to increase thermal refuge habitat availability. Because of the additional design and permitting requirements for channel planform modification, and the significantly greater cost, it is more feasible in the near term to develop a simple design for Gold Creek that involves installation of instream logs in a cost effective, low impact manner. Option 1 was therefore selected for design as part of this project. The design steps involved first mocking layouts and evaluating the resulting flow and temperature fields using a 2-D model, and reviewing the results to identify a suitable layout that will result in extending the cool water plume during the late summer when adult Chinook Salmon begin to migrate upstream in the Sammamish River. The layout was then evaluated for structural stability and construction requirements as influenced by buoyancy, drag, and scour, followed by an assessment of effects on the 100-year flood level. These steps are described below. The resulting design is depicted on scaled CAD drawings in Appendix E. This design is a feasible project, however, it should be noted that additional design analysis could potentially lead to an optimized design that maximizes thermal refuge habitat benefits at the site. In addition, there are several aspects of the design process that are identified below that could potentially lead to future design modifications.

5.2.1 2-Dimensional (2-D) Modeling of Flow and Temperature A 2-D hydrodynamic and temperature model was developed for use as a habitat restoration design tool. The model simulates depth, velocity, and temperature distributions in the confluence region during low summer flows based on channel morphology, channel roughness, turbulent mixing characteristics, and flow and temperature inputs from upstream in the Sammamish River and Gold Creek. Because the project reach is straight and essentially prismatic, and the Gold Creek channel is small relative to the Sammamish River channel, we have reasonable confidence that a 2-D approximation of the flow and temperature fields is sufficient to evaluate benefits of the project design. Preliminary analysis using SSTEMP, a one-

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dimensional temperature model developed by the USGS, indicated that the reach was sufficiently short that heat accumulation from other sources is negligible in the model reach. In addition, the model was used to evaluate the effect of augmenting summer flows in Gold Creek in Section 6.

The modeling was performed using RMA2 v4.3.5, a finite-element 2-D hydrodynamic numerical model, coupled with RMA4, a 2-D water quality transport numerical model. Both models are supported by the U.S. Army Corp of Engineers. RMA2 was used to predict water depths and depth-averaged velocities throughout the reach during low flows, when elevated water temperatures are most adverse for upstream migrating Chinook salmon adults in the Sammamish River. RMA4 was used to calculate the dispersion of water temperature based on the advection- diffusion process using depth and velocity characteristics predicted by RMA2.

The bathymetric and detailed temperature profile data collected in August 2010 were used to develop the model, along with additional survey data collected in December 2010 for the design. Figure 5-2 shows the model domain and bathymetry of the surveyed project area. Two modeling scenarios were identified for calibration and verification of simulated flow and temperatures during the summer period. Scenario 1 was run to calibrate the model to the hydraulic conditions measured on 8/25/10 when field data were collected, and Scenario 2 was run to evaluate its predictive ability using the field data collected on 8/13/10. Where necessary, the results for Scenario 2 were used to fine-tune the calibration.

The model was then run to evaluate predicted temperature distributions at a representative low flow and elevated water temperature in the Sammamish River for late August, with and without the design structure. Flows and temperatures were modeled to represent conditions on the August 25, 2010 sampling date (Table 3-3). The Sammamish River temperature was set at 20.7°C which was representative of most measurements in the unaffected portions of the Sammamish River over the course of the day. Benefits achieved at this flow and temperature should also be realized when temperatures are higher (a representative scenario approach was used for design evaluation because it was not feasible with the available budget to run a number of design iterations through the 2-D model).

Hydrodynamic Modeling: The confluence channel geometry was represented in the model as a network of mesh with 8-point rectangular or 6-point triangular quadratic elements. The mesh elements were arranged in a spatial pattern that reflects the numerical sensitivity of RMA2 to variable bathymetry and boundary conditions as it seeks a convergent, stable solution. Greater spatial resolution (i.e., smaller mesh element size) was applied in regions where spatial variation

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in depth, velocity, and temperature were greater (e.g., in velocity shear zones, and where the bed elevation changes rapidly with distance).

Figure 5-2. 2-D hydrodynamic model domain and bathymetry of the Gold Creek design site. Flow in the Sammamish River is to the top of the page; Gold Creek enters from the right bank.

RMA2 requires boundary condition nodes to always be wet during the simulation to avoid the solution becoming unstable and divergent. To accomplish this, the model bathymetry was adjusted at the Gold Creek inflow boundary by artificially lowering and then gradually increasing the bed elevations in the downstream direction to equal the surveyed bathymetry. This modification did not materially affect the predictions for locations corresponding to more than four to five elements away from the boundary. The mesh elements were divided into seven regions based on the bed and flow characteristics. Channel roughness, Manning‟s n, values and the eddy viscosity were estimated for each type of elements. The eddy viscosity is a coefficient that both reflects the flow turbulence intensity and facilitates the numerical stability.

Temperature Modeling: The water quality model RMA4 used the output from RMA2 to calculate the depth-averaged temperature distribution in the river. The calculation was based on the 2-D advection-diffusion equation with a turbulent mixing (dispersion) coefficient D, which

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was estimated using the Peclet number (Pe). The Peclet number is a non-dimensional coefficient equal to the ratio of advection term to diffusion term in the governing equation: udx Pe D where u is velocity and dx is element length in the streamwise direction. The mixing coefficient D was greater near the confluence where velocity shear was significantly greater than that in the far-field. Using the Peclet number allowed varying of the mixing coefficient with flow velocity and element size. A greater magnitude coefficient reflects more rapid mixing occurring in the confluence area. The temperature calibration process involved assuming a Peclet number for each region for the initial simulation run. The results were compared with field-measured temperatures at various locations. The assumed Peclet numbers were adjusted iteratively to reduce the differences between measured and simulated water temperatures until an acceptable range of errors was achieved. The calibrated values of Peclet numbers for each element region are summarized in Table 5-2.

Table 5-2. The seven finite element regions that were defined for the 2-D temperature modeling, and their corresponding eddy viscosity, Peclet Number, and Manning‟s n values. Eddy Viscosity Element Materials (lb-s/ft2) Peclet Number Manning's n Far-Field Mixing Zone 5 40 0.032 Gold Creek Bank 5 80 0.06 Gold Creek Channel 5 80 0.045 Near-Field Mixing Zone 20 80 0.032 Sammamish Channel 5 80 0.032 Aquatic Vegetation 5 40 0.08 Wood Structure 10 80 0.04

5.2.1.1 Evaluation of Design A second model mesh was subsequently developed from the calibrated existing conditions model that incorporated the design in Appendix E as a series of log-shaped protrusions from the riverbed. The two models were run and results compared for differences in predicted temperature fields between depth-averaged temperature distributions at the confluence of the Sammamish River and Gold Creek, for existing conditions and with the proposed alternative. The model predicts that the structure works as intended, effectively isolating and extending the cool water mixing zone laterally and downstream (Figure 5-3). The area contained within the

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predicted 19°C contour is approximately 1034 ft2 without the structure and 1968 ft2 with the design in place. Thus the structure increases thermal refuge habitat area by nearly 100% as defined by the 19°C contour.

Figure 5-3. 2-D hydrodynamic model temperature field predictions simulating without (top) and with (bottom) the proposed structure design detailed in Appendix E for the Gold Creek site;

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o o QSammamish=57cfs, QGoldCreek=2.9cfs, TSammamish=20.7 C, TGoldCreek=15.4 C, WSE at downstream boundary of Sammamish River is 996.16ft, based on local datum.

5.2.2 Design Overview The resulting design for the mouth of Gold Creek is presented in Appendix E. The design is simple and relatively inexpensive to construct, with construction cost estimated at $119,650 including contingency (Table 5-1). The design assumes that there are no complications involved in excavating a small trench partway into the right bank. The following criteria and objectives formed the basis of the design:

1. The design uses minimum 2 ft diameter logs as opposed to smaller logs which could require additional anchoring to one another as well as the bed to ensure stability; larger diameter logs also take longer to decay than smaller logs. The logs will remain submerged and are expected to last more than 20 years (e.g., Murphy and Koski 1989). 2. Maximum velocity influencing scour and anchoring design = 2.6 ft/s at the 100 year flood (HEC-RAS model result). A value of 4 ft/s was used in the design calculations of stability and scour. 3. The anchoring system shown on the plans involves a redundant combination of earth anchors and vertical boles driven into the bed to hold the logs in place against buoyancy and drag forces. One approach is sufficient to maintain anchoring should the other approach fail. The logs are fully submerged most of the time to prolong their working life. 4. The potential for scour was evaluated along the downstream side of the upper logs and the results used to specify river gravel size. The rock size and placement specifications on the plans are sufficient to prevent undermining of the logs and subsequent underflow by the river. In addition, rock is placed on the upstream side of the upstream diagonal log to create a more efficient hydraulic transition for flood flows, thereby reducing the risk of affecting flood water surface elevations. 5. The top elevation of the logs starts at the upstream end at around the median summer water surface elevation to block and route warmer Sammamish River water around the mouth of Gold Creek. The logs follow the bathymetry in the downstream direction, sloping gently down and allowing some overflow towards their downstream end. A hydraulically sheltered 1 ft wide notch is maintained between the upper cross logs and the upstream set of streamwise-oriented logs to permit adult salmon to swim upstream without restriction. This configuration acts to reduce mixing of Sammamish River and Gold Creek water, and the logs also provide object cover for the salmon.

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6. Two logs are constructed side-by-side along the length of the structure, and gravel filled within the gap. The intent is to provide an eventual rooting medium for aquatic vegetation that provides additional sheltering of the mixing zone. During the winter, the vegetation should die back and not influence flood flow water surface elevations. 7. Both banks are restored with native trees, shrubs, and ground cover, following general King County protocols to eradicate invasive species and plant native vegetation.

5.2.2.1 Design Limitations While we believe the design as presented can be permitted, bid and constructed as drawn and specified with limited risk to the project owner, there are uncertainties that may influence the permit process and the feasibility and cost during construction that remain to be considered (but were not within the general scope permitted by the available budget for this work). These uncertainties include:

The extent to which adult Chinook salmon would use the logs as cover or avoid them is unknown.

A utility locate should be performed to confirm no water, gas, electric, or telecommunication lines exist within the project footprint. If found, the design may need to be revised accordingly.

A property boundary survey may be required if any landownership lines are in doubt or a right of way or construction access easement is required.

A geotechnical survey and design may be required by King County to address levee stability requirements. A comparable geotechnical engineering study was performed for the City of Redmond‟s HEP IV project located upstream of the Gold Creek site (GeoEngineers 2005). That study generally found silt and fine sand in the upper 15 ft or so of most test borings. Gravel was found in some locations at depths that may be consistent with the general river bed elevation. In some borings, pockets of peat were found. The type of material encountered at the Gold Creek site could influence the design of anchoring method(s) ultimately used. Anchoring is extremely important, because an instream log structure that gradually loosens could begin oscillating at high flows and cause unanticipated scour and bank damage.

Temporary wetland impact mitigation could be required by DOE as a condition for permitting.

Water quality monitoring and additional sediment control measures may be required during construction as a condition for permitting.

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Additional hydraulic modeling for no-rise certification.

Additional design analyses of other possible configurations to optimize the thermal refuge habitat area enhanced starting with the present design. It is our judgment that these uncertainties will need to be addressed as part of the implementation phase for the project. In addition, we also recommend further assessment of Options 2 and 3 for this site, involving re-meandering the Sammamish River through the locations of the existing topographic depressions along the west bank.

5.2.3 Assessment of 100-yr Flood Zero-Rise Criterion Chapters 24.240 through 24.250 of Title 21A of the King County Code (KCC) address zero rise requirements for projects within the floodway. An aquatic fisheries habitat enhancement project such as that proposed for Gold Creek is allowed if the proposal is approved by all agencies with jurisdiction and meets development standards of the zero rise floodway. Compensatory floodplain storage volume is required under the KCC, as is no net increase in the 100 year flood in response to the project. Because the proposed structure would act as an obstruction to the flow and reduce the conveyance area, hydraulic analysis using a generally accepted model such as HEC-RAS will generally predict an increase in water surface elevation upstream of the structure. In order to meet a zero-rise criterion through hydraulic analysis, the design will need to include compensatory increase in conveyance that results in predicted water surface elevations upstream of the project with and without the project that are comparable. In the present design, such compensation will be provided by cutting back one or both banks. Other designs could evaluate the possibility of excavating into the floodplain, although this would likely require considerably more excavation than if the banks are modified because of reduced hydraulic efficiency of flow over the floodplain.

Accordingly, R2 obtained a copy of a steady flow HEC-RAS model titled SammamishRiverFIS from Carolyn Butchart, King County River and Floodplain Management Section. The model was developed for a Flood Insurance Study (FIS) as part of a January 25 2010 submittal to FEMA. We reviewed the model and concluded it to be satisfactory for the purpose of evaluating potential changes in stage due to the project to meet the no-rise requirement. The model geometry extends between Lake Washington and Lake Sammamish. The Gold Creek site is represented in the model by the cross-section at Station 37100.64. The model uses estimates of the 100 yr flood magnitude presented by NHC (2010) for the following reaches:

1. Lake Sammamish to Bear Creek (1,649 cfs) 2. Bear Creek to NE 116th St (2,591 cfs)

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3. NE 116th St to NE 145th St (2,721) 4. Little Bear Creek (2,843 cfs) 5. Little Bear Creek Confluence to North Creek Confluence (3,326 cfs) 6. North Creek Confluence to Swamp Creek Confluence (4,374 cfs) 7. Swamp Creek Confluence to Lake Washington (5,255 cfs)

These flows are higher in magnitude than values estimated previously by Hartley and Stuart (2004).

The selected alternative was modeled in HEC-RAS as an obstruction situated on the bed of cross-section 21, located near the mouth of Gold Creek. The upstream logs in the design are angled away from the bank at approximately 45°C for a short distance above the confluence and the downstream logs are aligned more closely to the flow streamlines in the downstream direction. As a worst case analysis, we treated the effective obstruction cross-section area as a 10 ft wide obstruction with height determined by the size of the structure. For a 2 ft high log, this amounts to 20 ft2, or nearly double the actual cross-section slice through the logs, which presents a projected obstruction cross-section area of approximately 11.3 ft2. The logs extending downstream at an angle are in the hydraulic shadow of the upstream end and also present a minimal cross-section area. Figure 5-4 depicts the cross-section representation in HEC-RAS, without modification of the bank.

SammamishRiverFIS Plan: 1) Plan 01 12/21/2010

. .08 .045 .08 .045 35 1 Legend 5 WS 100 yr 0.5 ft/s 1.0 ft/s

1.5 ft/s 30 2.0 ft/s 2.5 ft/s

3.0 ft/s Ground Ineff 25

Bank Sta Elevation(ft)

10 600 700 800 900 1000 Station (ft) Figure 5-4. HEC-RAS cross-section at River Station 37100.64 with a 10 ft wide by 2 ft high flow obstruction added to simulate the effects of the proposed structure on the flow field. The

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100-year flood water surface elevation is depicted. Predicted mean channel velocity = 2.65 ft/s.

The water surface elevations for the existing and proposed project conditions were compared to evaluate changes potentially resulting from the obstruction. With just the structure in place, no grading with cobble and gravel upstream to produce a converging flow field approaching the structure (which is more hydraulically efficient), and no compensatory increase in conveyance through cutting back of the riverbanks, the model predicts an increase in stage of 0.01 ft (from 29.54 ft to 29.55 ft), which is within standard model error bounds (FEMA allows for a +/- 0.5 ft prediction error in delineating the 100-year floodplain). The design thus appears to be compatible with flooding processes and does not appear to present an additional risk of flood impacts in the reach due to its small cross-section profile and approximate orientation with high flow streamlines. If the County does not accept the 0.01 ft prediction error and demands that the model predictions show a zero difference numerically as a condition for final permitting, the design could be modified further where the left and/or right bank can be cut back sufficiently that the model predicts a flood stage of 29.55 ft. This would require additional HEC-RAS modeling and bank stabilization design, however. Preliminary modeling analysis indicates that the right bank would need to be cut back by more than 1 ft to accomplish this using HEC-RAS, where the corresponding increase in cross section area exceeds 40 ft2 (given that the effective cross-section area of the structure is 20 ft2 = 10 ft wide x 2 ft high, this difference illustrates the potential error in model predictions). Alternatively, the present design could be modified to reduce the amount of excavation needed if the effective cross-section area presented by the structure is reduced below that proposed here (e.g., a 5 ft long log at the upstream end instead of a 10 ft long log).

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6. POTENTIAL BENEFITS OF INCREASING TRIBUTARY SUMMER FLOWS TO IMPROVE THERMAL REFUGE HABITAT IN THE SAMMAMISH RIVER

As described in Section 1, flow augmentation of selected tributaries is a potential alternative approach to designing and building structural measures to increase thermal refuge habitat availability in the Sammamish River during warm summer months. One possibility that has been identified is to pump treated effluent from the new King County Brightwater sewage treatment facility into the ground to increase the groundwater table elevation and thus flow rate into tributaries. Another possibility is to manage groundwater pumping where it is reduced or halted at appropriate times to increase summer low flows in selected tributaries (e.g., Bear Creek; Carey 2003). This project was conceived in part to more thoroughly evaluate the feasibility of flow augmentation in terms of likely effects to temperature mixing zones in the Sammamish River at tributary confluences.

We evaluated the relation between tributary and mainstem flows and water temperatures in three ways: theoretically, empirically, and numerical modeling of the Gold Creek site. The evaluations are described below in this section. A key objective of the work was to assess the potential benefits of flow augmentation, and additionally, help guide future strategic decisions as to whether thermal refuge habitat availability can be best improved by physical/structural means or by flow augmentation.

6.1 THEORETICAL ANALYSIS We performed a simplified, first order analytic assessment of temperature mixing dynamics in the Sammamish River for two purposes. The first was to inform planning of detailed field temperature data collection at the selected sites. Knowledge of the approximate mixing field extent that might be encountered allowed us to anticipate the required spatial distribution of point samples. The second purpose was to assess theoretically the potential benefits of flow augmentation. By running a number of scenarios involving different combinations of mainstem and tributary flows and temperature differences, it was possible to generate surface response curves relating available habitat refuge area to the relative differences in flow and temperature. The results provide an approximate indication of how much tributary flow would be needed to increase habitat area in a biologically meaningful way, for different temperature contours within the mixing zone.

For simplicity, a tributary was represented as a point source on one bank. The width and depth of the Sammamish River were approximated as 60 ft and 2.4 ft, respectively, based on aerial

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photographs and depth data collected as part of the longitudinal profile survey. It was assumed that the mixing zone of temperature increased linearly in width across the channel until it reached the other bank. The corresponding length of channel between the point source and the point where the mixing zone reached the opposite bank was set as the mixing length L. The cross-section distribution of temperature across the mixing zone was simplified as a triangular approximation (as opposed to a Gaussian distribution; Fischer et al. 1979), with maximum value at the bank and zero value at the edge of the mixing zone. The temperature at the bank for a given distance downstream was estimated using an analogous relation for concentration depicted in Figure 5.5 of Fischer et al. (1979):

where x = distance downstream from the point source, εt = transverse mixing coefficient (0.8 ft2/s), ū = mean streamwise velocity (0.52 ft/s), and W = width (60 ft). The depths and velocities were estimated from the long profile depth data and flow at King County gage 51T, and the transverse mixing coefficient value was estimated based on previous work performed at the mouth of North Creek (R2 2009a,b). Applying this to the cross-stream distribution allowed calculation of the approximate location of the temperature contour at any point across the mixing zone. This was performed for temperature differences of 6°C, 5°C, 4°C, 3°C, 2°C, and 1°C between mainstem and tributary, and for different levels of mainstem flow (60 cfs, 80 cfs, and 100 cfs). The results are self-similar for different temperatures specified for the Sammamish River, so a value of 20°C was used in the analysis to represent the general range encountered in the field. Figure 6-1 depicts an example result for 60 cfs in the Sammamish River, 9 cfs in the tributary, and a 6°C temperature difference between Sammamish River and tributary. Similarly appearing curves are obtained for other combinations.

The area within each contour was then calculated in a spreadsheet. Compiling the resulting areas calculated for a range of tributary flows (expressed as a percentage of the upstream Sammamish River flow) and temperature differences results in a characteristic surface response curve such as that depicted in Figure 6-2. The main conclusion that may be inferred from Figure 6-2 is that the theoretical analysis suggests that flow augmentation is unlikely to have a substantive, biologically meaningful effect on thermal refuge habitat availability at the confluence of tributaries that contribute less than approximately 10 percent of the Sammamish River flow, and where the temperature difference between tributary and mainstem is less than about 3°C. This conclusion is evaluated further in the next section using the detailed field temperature data collected in July and August 2010.

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Temperature Contours (oC) 10

7 19.0

6 18.5

5 18.0

4 17.5

3 17.0 Stream Distance (ft) from Bank Stream

- 2

1 Cross 0 0 200 400 600 800 Longitudinal Distance along Bank (ft)

Figure 6-1. Example calculation of temperature contours for a simplified representation of the Sammamish River with a tributary point source located at the axes origin. The area enclosed within the 18°C contour is illustrated by light shading. River flow (60 cfs) is left to right, tributary flow = 15% of river, mainstem/tributary temperatures = 20°C/14°C.

6.2 FIELD DATA ASSESSMENT The field data can be represented graphically in a similar manner as the theoretical analysis results depicted in Figure 6-2. We used the default Kriging gridding algorithm in Surfer to plot the data in Table 3-4, resulting in the surface response plot of Figure 6-3. There are similarities indicated between the two plots, where thermal cooling of the tributary is substantially greater when the tributary flow is more than about 10%-14% of the mainstem flow, and temperature differences between the two exceed 2-3°C. Below about the 5% flow level, the data indicate there is relatively little thermal cooling habitat available when temperature differences are less than about 5°C (Figure 6-3). Between about the 5% and 10% flow levels, increases in flow result in modest increases in cooler water volumes. Interestingly, however, the empirical data indicate a relatively greater availability of thermal cooling volume compared with the theoretical area analysis within that flow range (cf. Figures 6-2 and 6-3). Field observations of adult Chinook distributed over the water column at thermal refuge sites (E. Warner, MITFD, personal communication) imply that increases in thermal refuge habitat volume can have biological benefits at relatively small tributary confluences.

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The results in Table 3-4 were analyzed further using multiple linear regression analysis to evaluate if a predictive relation could be identified. The shape of the curves in Figures 6-2 and 6-3 suggest that a bivariate exponential polynomial could be fit to the data to generate a predictive surface response curve that could potentially be useful in planning future flow augmentation projects. Volume was evaluated as a function of the percent of the flow that comes from the tributary and the increase in degrees Celsius above the tributary temperature for each temperature contour. The number of data points used for each site varied depending on the number of times the site was visited, the spatial extent that could be sampled within the 6 hour period between 2 pm and 8 pm, and the difference in temperature between the tributary and the mainstem Sammamish River. There were accordingly more data points for those sites with a larger temperature differential since those sites have more contours. In all, there were a total of 70 data points used in the regression analysis.

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Figure 6-3. Surface response curve generated for measured available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. The irregular peaks in the mid-range of flows reflect the scatter of data from North, Little Bear, and Gold creeks (cf. Table 3-3).

The exponential polynomial model evaluated had the general form:

where V= volume (ft3), Q = percent of the flow from the tributary, T = difference between the temperature contour and the tributary temperature (°C), and a, b, c, and d are the regression fitting coefficients. Higher order terms involving Q2 and T2 were evaluated for potential inclusion in the polynomial but were rejected for several reasons. A least-squares, stepwise regression analysis was performed using the R statistical programming package (http://www.r- project.org/) to test additional model variables for significance. A backward elimination process was used which started with all variables and then deleted those that were not significant. The Akaike‟s Information Criterion (AIC, Burnham and Anderson 1998) procedure was used to rank the competing models. The results indicated that the T2 term did not contribute significantly

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toward explaining variation in volume. The Q2 term was not rejected on statistical grounds. However, the resulting coefficient was negative which resulted in the model predicting lower volumes at high tributary inflows, which does not make physical sense, and thus this term was also rejected from further consideration.

The results of including all first order terms and just the Q and T terms are presented in Figure 6-4. The flow-temperature interaction regression coefficient estimate was not significantly different from zero at the 5% confidence level. A plot of predicted vs. observed points indicates there is considerable remaining variability that is unexplained by the selected model (Figure 6-5). Elimination of the non-significant D-V correlation term did not result in a substantially different model (Figures 6-4, 6-5). The simpler model predicts volumes that are closer in magnitude to observed, whereas the interaction term model better describes volumes measured at intermediate flows and temperature differences. Importantly, the models generally resemble the shape of the surface response plot in Figure 6-2, and support the inferences made above from the theoretical analysis. However, the residual differences in the mid-range of flows between Figures 6-3 and 6-4 indicates that efforts to develop a more representative statistical prediction model would require increasing the sample size and performing more sophisticated statistical analysis.

6.3 2-D MODELING AT GOLD CREEK SITE The physically-based 2-D model developed for the Gold Creek site was also run to predict temperature distributions for different combinations of flow and temperature in Gold Creek relative to the Sammamish River. To compare with the theoretical results in Section 6.1, a flow of 60 cfs was specified for the Sammamish River upstream boundary condition, with an ambient river temperature of 24°C. The temperature in Gold Creek was fixed at 15°C, the approximate average for the two dates on which detailed temperature measurements were collected. It was assumed that increases in tributary flow in response to an increased groundwater table would not be substantially cooler. Three flows were modeled for Gold Creek, consisting of 3 cfs (slightly above general level measured in July and August 2010), 5 cfs, and 7 cfs, which equate to 5%, 8.3%, and 11.6% of the upstream flow in the Sammamish River, respectively. The simulation results are generally similar to the preceding simplified model results when represented as a surface response curve, where greater habitat area occurs when the temperature difference between tributary and mainstem exceeds about 3°C (Figure 6-6). The primary difference between the two model predictions is that the 2-D model predicts a greater amount of area bounded by the 19°C and 20°C contours for tributary inflows between 5%-10% of the mainstem flow. In addition, whereas the simplified Excel spreadsheet model predicts that the rate of increase in area is much greater when the percent of mainstem flow exceeds about 10°C (Figure 6-2), the 2-D model predicts the transition to occur closer to about 8°C (Figure 6-6).

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Figure 6-4. Surface response curves of regression model predictions of available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. Top: model including flow-temperature interaction term; Bottom: model excluding interaction term.

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Regression Model: Volume

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Figure 6-5. Regression model predictions of available habitat volume as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence. Top: model including flow- temperature interaction term; Bottom: model excluding interaction term.

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In summary, the collective modeling and empirical results indicate that flow augmentation in Gold Creek would not be expected to substantially increase thermal refuge habitat area and volume for adult Chinook salmon in the river until the tributary flow rate exceeds somewhere around 8%-10% of the mainstem flow rate. Given a current flow percentage of around 3-5% of mainstem flow (Table 3-3), this means that a minimum increase in flow of approximately 2 cfs would be required before substantial thermal benefits can be achieved with additional flow augmentation.

Figure 6-6. Surface response curve for the Gold Creek site of available habitat area predicted by the 2- D hydrodynamic-temperature model as a function of temperature contour (expressed as increase over tributary inflow temperature) and the ratio of tributary inflow to Sammamish River flow upstream of confluence.

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7. DISCUSSIONS AND CONCLUSIONS

7.1 DISCUSSION It was somewhat unfortunate that water temperatures were generally on the cool side in the spring and summer of 2010. We were not able to get many detailed temperature measurements of the thermal mixing zone that were characteristic of extreme conditions encountered by adult Chinook salmon in the Sammamish River. Nonetheless, the data that were collected and analyses we performed appear to be sufficient for identifying the most important tributaries providing thermal refuge habitat to adult Chinook salmon migrants, and provide a quantitative indication of the relation between tributary-river flow and temperature differences. Based on this information, it was possible to rank and prioritize sites for thermal habitat enhancement, and identify specific, conceptual structural measures that could be implemented at five sites with greatest potential benefit to holding adult salmon.

The study findings point to four tributary confluences providing key thermal refuge habitat: Bear Creek, Gold Creek, Little Bear Creek, and North Creek. These streams each contribute from roughly 3% to more than 20% of Sammamish River inflow and a thermal mixing zone can be defined clearly at each confluence. Swamp Creek is not included in this list despite its larger drainage area because its confluence location is also under the influence of the Lake Washington vertical temperature profile and there is a long, warming backwater section at the lower end of the tributary. Other smaller tributaries have minor to negligible influence on thermal conditions in the Sammamish River that would be biologically meaningful to adult Chinook salmon, with the possible exception of Tributary 0091. In most cases, the mixing zone was either non- discernable or was restricted to a very small volume in relatively shallow, exposed water located away from the thalweg where adults would be less likely to swim to or through. Tributary 0091 may be an exception because while the mixing zone is relatively small, it extends partially under the NE 145th Street bridge which provides shade cover. In the case of Tributary 0142 where there is a larger area of cooling than at most smaller tributaries and where water lilies provide cover, the mixing zone is located away from the thalweg at a point near the lake outlet where slight vertical stratification in Lake Sammamish near the surface may provide a migration behavior cue competing with the shallow-water habitat. The possibility therefore exists that Chinook adults passing the weir quickly migrate into the deeper, relatively cooler water of Lake Sammamish, however, further investigation would be needed to answer this question more definitively.

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Thermal stratification of pools was generally found to be negligible upstream of North Creek. There was some stratification evident between North Creek and Horse Creek that may reflect a stronger groundwater influence than elsewhere in the river. However, the maximum difference between surface and bottom temperatures measured in this reach during the longitudinal profile survey was 0.25°C, which does not appear to be large enough to feasibly increase thermal refuge habitat availability without significant (and likely costly) additional study and design. Bottom temperatures below Horse Creek become influenced by Lake Washington where surface-bottom temperature differences in that lower reach gradually increased in the downstream direction. Upstream of North Creek, surface-bottom temperature differences were generally less than 0.11°C, with most measured differences ranging between 0°C and 0.02°C (Figure 3-3). Fresh et al. (1999) reported measuring differences exceeding 2°C at locations used by holding Chinook salmon but it was not reported where this occurred. The measured differences are generally small and suggest a limited influence of groundwater on near-bottom temperatures overall in the alluvial valley reaches upstream of North Creek. If thermal conditions are to be improved in pools, understanding groundwater flow patterns and finding ways to increase and/or concentrate inputs to the river will be keys to success. The small difference between surface and bottom temperatures suggests that structural measures presently would be unlikely to result in substantially increasing thermal refuge habitat availability in pools that are not directly influenced by point source tributary inflows.

The effect of restoring riparian shade was not addressed in this study. The work of DeGasperi (2001, 2005b) addresses this issue more fully. Modeling predictions have generally indicated in that work that benefits could be achieved through mature shading of the entire river corridor, although the benefits would be cumulative in the downstream direction. Consistent with this, the designs described in this report generally include re-vegetation as a universal component.

Several potential structural modifications are identified in Section 5 for the five sites with greatest potential for enhancing adult Chinook salmon thermal refuge habitat. Two general measures appear feasible for thermal enhancement at tributary confluences. The first, which involves construction of physical structures instream to retard mixing and extend the cool water plume downstream, is substantially less expensive to implement than the second, which involves reconstructing the river to a meandering planform. However, in principle, channel meandering could result in longer term benefits. Design- and permitting-related requirements and costs are likely to be considerably less for the simpler instream structure approach which involves limited channel disturbance and effects on flood levels. As described in Section 5, estimated costs associated with channel reconstruction can exceed $1,000,000 for even a relatively small channel meandering project on the Sammamish River. For the project upstream of the NE 85th Street

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bridge; the final construction cost was on the order of $2,000,000 (Roger Dane, City of Redmond, personal communication). The cost estimates presented in Table 5-1 should be considered as idealized with no surprises, such that the potential limitations identified for the costs and the final design should be considered carefully in subsequent project planning.

Of the five sites, the ranking system described in Section 4 suggests that Gold Creek may be the most feasible presently for enhancing thermal refuge habitat for adult Chinook salmon migrants, reflecting the limited constraints and thermal characteristics of the confluence. Costs of the recommended project are relatively low.

The Bear Creek site has the greatest potential area of thermal mixing zone expansion. However, plans by the City of Redmond to completely relocate lower Bear Creek and move the mouth downstream approximately 100 ft, together with the observation of warmer than expected temperatures in Bear Creek provide uncertainty to a decision to continue with designs at this site presently. It is recommended that, assuming the design has not been finalized yet, it ultimately factor in provision of thermal refuge habitat. For example, the design might be modified to, at worst, minimize the potential for loss of thermal refuge habitat by evaluating scour and sedimentation, and at best, lead to expanded thermal refuge habitat. The temperature increases that appear to occur in lower Bear Creek warrant additional study as well.

Of the remaining three sites in Section 5, the Tributary 0091 site was identified because it had a relatively large cooling influence for a small tributary and an enhanced mixing zone would extend under a bridge that provides shade cover. This site was not selected, however, because of potential infrastructure-related complications that could significantly increase project costs for an instream structure that would likely provide a limited additional volume of thermal refuge habitat overall. The site would be highly appropriate, however, for structural enhancement in conjunction with any future bridge work. The North Creek site had already been evaluated previously in a study for the City of Bothell but was not selected at this time because of potential impacts to recreation and private property that could significantly influence design development. The Little Bear Creek site was not selected because additional analysis would be required to address a heavy gravel bedload depositing out of the creek at the mouth without impacting spawning habitat used by sockeye salmon (O. nerka), and relatively heavy recreation use of the stream at this location.

In the context of applying flow augmentation as a restoration tool, the three different analyses described in Section 6 of the relation between tributary and mainstem flows and temperatures yield generally consistent results. It appears that summer flow augmentation will have relatively

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little effect unless the tributary contributes more than approximately 5% of the river inflow to the confluence during the low flow period, and the temperature difference between tributary and river temperatures exceeds about 3°C. Greatest increases are expected when the tributary contributes between more than 8%-10% of the river flow. While horizontal area of thermal mixing shows relatively little predicted increase between the 5%-10% flow levels, the empirical data suggest that the volume of thermal mixing may increase more substantially than area within this range, and increases at an even greater rate when flows exceed the 10% level. Based on this, it is inferred from Tables 3-3 and 3-4 that flow augmentation would benefit Bear Creek the most, followed by North Creek, Little Bear Creek, and Gold Creek, in order from highest to lowest benefit. In the case of Gold Creek, we infer from the analysis results that flow augmentation would require a minimum increase of about 2 cfs before more substantial increases in thermal volume might be realized. These inferences have some uncertainty associated with them because of the relatively narrow range of temperature differences sampled at the larger tributary sites (Figure 7-1). Additional detailed temperature data collection at these sites over a higher range of mainstem temperatures would provide greater variation in the temperature conditions sampled in Gold Creek and the larger tributaries, and thus potentially lead to greater certainty regarding the conclusions of this study regarding flow augmentation.

Although the two approaches are not mutually exclusive, it is reasonable to ask which holds greater promise in enhancing thermal refuge habitat conditions in the Sammamish River: instream/channel planform structural measures applied to the river channel, or summer flow augmentation in tributaries? Our work did not involve an exhaustive analysis comparing and contrasting potential increases in thermal mixing zone volumes due to one approach vs. the other. The 2D modeling results for the final design at the Gold Creek site provide an initial indication, however. As described in Section 5.2.1, the model predicts an increase of approximately 930 ft2 of habitat area having water temperatures less than 19°C with the structure in place compared with baseline conditions without a structure. To achieve the same level of increase using flow augmentation would require summer flows in Gold Creek to be increased by more than 2 cfs to equal roughly 10% of the Sammamish River inflow. This result suggests that equivalent benefits may be realized through construction of instream structures to retard mixing and through flow augmentation in Gold Creek given enough flow. Future assessments of feasibility and site-specific opportunities to augment tributary and groundwater inflows for thermal refuge habitat enhancement could be part of ongoing work in the development of the King County Reclaimed Water Comprehensive Plan (http://www.kingcounty.gov/environment/ wastewater/ReclaimedWater/CompPlan.aspx). The assessment should consider the possibility for different levels of effect based on tributary size. For example, Figures 6-2 to 6-4 imply substantially larger benefits in larger tributaries for the same absolute increase in flow rate.

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C) ° 7

Tributary; Tributary; 6 -

Temperature Difference (Mainstem TemperatureDifference 0 0% 5% 10% 15% 20% 25% Tributary Input as Percent of Mainstem Inflow to Confluence

Figure 7-1. Range of observed temperature differences and flow percentages in the Sammamish River and tributaries for which detailed temperature data were collected at tributary confluences in July and August 2010.

7.2 CONCLUSIONS AND RECOMMENDATIONS The following key conclusions and recommendations are made from this study:

Four tributaries are of greatest importance for protecting flows and water temperatures to benefit adult Chinook salmon migrants: Bear Creek, Gold Creek, Little Bear Creek, and North Creek. Efforts to protect and enhance thermal refuge habitat in the Sammamish River should focus on these locations first for greatest benefits to adult Chinook salmon migrants. Tributary 0091 may also provide a potential opportunity. Conditions at the mouth of Swamp Creek may not be presently conducive to thermal refuge habitat enhancement.

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Two general concepts involving structural measures can be potentially implemented in the Sammamish River at the above sites to enhance thermal refuge habitat: o Constructing an instream structure to separate the tributary inflow from the main river flow, thereby retarding mixing and extending the cooler water plume downstream; and o Reconstructing the river to a meandering planform where a bend scour pool would be created and maintained at a tributary confluence. The feasibility and effectiveness of this measure remain to be investigated, however.

Instream structures would be at least an order of magnitude cheaper to design, permit, and construct than channel meandering. Constructed channel meanders would persist for longer, however, and benefits of instream structural measures would be more certain with improved understanding of adult Chinook salmon behavior around log structures in the Sammamish River. The Gold Creek, Bear Creek, and North Creek sites would support one or both conceptual designs; the Tributary 0091 site would best support an instream structure design, whereas the Little Bear Creek would best support a limited channel meandering design.

Efforts to enhance thermal conditions at the mouth of Bear Creek should reflect planned future changes in the confluence location, and changes in temperature within the lower reach of Bear Creek. These potential constraints have implications for a temperature project in the Sammamish River in the context of risks to the quantity of thermal refuge habitat compared to current conditions.

Efforts to enhance thermal conditions at the mouth of Little Bear Creek will need to include more detailed study and analysis of potential bedload impacts at the confluence before continuing with the conceptual design.

Tributary 0091, located on the left bank immediately upstream of the NE 145th Street bridge is located at roughly the same mid-point on the Sammamish River migration route as Gold Creek for Chinook salmon headed to Bear Creek and Issaquah Creek. Its proximity could thus complement the Gold Creek site. This project would provide a good opportunity for mitigation as part of future bridge work.

Pools between North Creek and the weir controlling outflow from Lake Sammamish at Marymoor Park that are not linked to tributary outflow appear to be associated with negligible thermal refuge habitat. The success of efforts to increase thermal habitat availability in pools in this reach will likely depend more on increasing groundwater inflow than relying on instream structural measures.

Summer low flow augmentation appears to have greatest potential benefit in Bear Creek, followed by North and Little Bear creeks, because their contributing flow rates are

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already high and relatively large mixing zones already exist in portions of the channel likely to be used most by adult Chinook salmon. Flow augmentation benefits are also potentially possible at the Gold Creek site.

Additional data and analysis are required to determine which general measure, structural habitat modification or flow augmentation, would be optimal for increasing adult Chinook salmon thermal refuge habitat at each specific tributary confluence. Based on our results, we hypothesize in the case of the smaller tributaries that increases in thermal refuge habitat may have greatest biological benefits when associated with structural measures. Both measures appear to be effective in the case of Bear Creek, Gold Creek, Little Bear Creek, and North Creek, but more detailed data collection, analysis and design would be needed to identify optimal approaches there.

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