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HomeMy WebLinkAbout1995 Restoration Feasibility Study for Big Quilcene RiverA Restoration Feasibilit�� Stud- f or th e Big ui c er F-Tr'w ------ wart PHILIP WILLIAMS & ASSOCIATES. LTD. C o n s u i I a n t s i n H y d r o I o g y r Philip Williams & Associates, Ltd. Consultants in Hydrology A RESTORATION FEASIBILITY STUDY FOR THE BIG QUILCENE RIVER Prepared for Washington Wildlife Heritage Foundation Prepared by Philip B. Williams, Ph.D., P.E. President Larry Fishbain, P.E. Associate Kevin G. Coulton, P.E. Associate and Brian Collins Consulting Geomorphologist August 1995 #1033 950\D:\ERICA \WORKING \1033FEAS.DO8 et wp6.1 \9/6/95 Pier 35, The Embarcadero San Francisco, CA 94133 Phone (415) 981 -8363 Fax (415) 981 -5021 e -mail: PWA_LTD @delphi.com Environmental Hydrology Engineering Hydraulics Sediment Hydraulics Water Resources Printed on Recycled Paper TABLE OF CONTENTS Pate No. I. INTRODUCTION I II. CONCLUSIONS AND RECOMMENDATIONS 2 A. CONCLUSIONS 2 B. RECOMMENDATIONS 3 III. EXISTING CONDITIONS AND PROCESSES s A. PHYSICAL 1. Hvdrologv 2. Sediment Transport 6 3. Geomorphic Evolution 7 B. ECOLOGIC FUNCTIONS IV. GOALS AND OBJECTIVES 14 V. OPPORTUNITIES AND CONSTRAINTS 16 A. OPPORTUNITIES 16 B. CONSTRAINTS 16 VI. DESCRIPTION OF ALTERNATIVES 18 A. NO ACTION ALTERNATIVE (ALTERNATIVE 1) 18 B. RESTORATION ALTERNATIVES (ALTERNATIVES 2, 3 AND 4) 19 k50VD:AERICAAW0RKINGVI033FEAS. D08 et wpb 1A916/95 1 VII. ASSESSMENT OF ALTERNATIVES A. GEOMORPHIC EVOLUTION 1. General 2. Channel Aggradation 3. Channel Switching 4. Channel Form 5. Channel Structure B. FLOOD HAZARDS 1. Flood Elevations 2. Resilience of the Design to Extreme Events C. HABITAT D. COSTS 1. Capital Costs 2. Maintenance Costs REFERENCES N50\D:\ERICA\ WORKING \1033FEAS. D08 et wp6.1 \4/6/95 ii Page No. 23 23 23 23 25 25 26 26 26 28 28 30 30 30 32 LIST OF FIGURES Figure 1. Watershed of the Big Quilcene River Figure 2. Annual Hydrograph Figure 3. Flood Frequency Figure 4. Floodplain Map Showing Study Reach Figure 5. Geomorphic Evolution of Delta Figure 6. Natural Channel Structure Figure 7. Channel Profile Figure 8. Historic Profile Change Figure 9. Photo of Mouth of Quilcene River in Flood December 1987 Figure 10. Peak Count of Early Chum Salmon per mile in the Quilcene River Figure 11. Potential Channel Switching Paths Figure 12. Typical Cross - Section in Lower River Figure 13. Alternative 2 Figure 14. Alternative 3 Figure 15. Alternative 4 Figure 16. 2 -year Flood Water Surface Profile Post Construction Figure 17. 2 -year Flood Water Surface Profile after 30 Years Figure 18. 10 -year Flood Water Surface Profile Post Construction Figure 19. 10 -year Flood Water Surface Profile after 30 years 950 AD.AGRIGUWORKINGA1033FHAS.DO8 et wpb. 1A9/6/95 111 LIST OF TABLES Table 1. Summary of Comparison of Alternatives Table 2. Potential Impact of Channel Switching Table 3. Equilibrium Geometry of the Big Quilcene River Table 4. Summary of Alternatives Table 5. Potential Channel Aggradation Over the Next 30 Years Table 6. Relative Degree of Maintenance Activities Table 7. 2 -Year Flood Characteristics Table S. 10 -Year Flood Characteristics after 30 years Table 9. Capital Cost Factors Table 10. Maintenance Cost Factors 450\D TR ICA\ W ORK ING\ 1033FEAS. DOS et wpb.1 \9/6/95 ly I. INTRODUCTION The lower Big Quilcene River and its delta have been identified as offering significant potential benefits for restoring fish and wildlife. In particular the critical stock of summer chum salmon that spawns in this reach has been experiencing significant declines in recent vears. At the same time, concern over flood hazards to adjacent property has led to periodic dredging of the channel and consequent disturbances to this critical habitat. The Big Quilcene Local Interagency Team (LIT) consisting of representatives of Jefferson County, Washington Department of Fish & Wildlife, U.S. Fish and Wildlife Service, the Point No Point Treaty Tribes and the residents of Quilcene, requested the Washington Wildlife Heritage Foundation (WWHF) to administer a contract to evaluate the feasibility of restoration in a manner that would not increase flood hazards. WWHF has contracted with Philip Williams & Associates, Ltd. (PWA) to carry out this analysis. PWA was instructed to formulate alternative restoration design strategies to identify potential habitat benefits, affect on flood hazard and likely grading and maintenance requirements. PWA would recommend a design approach to the team, which if selected would then proceed to construction design and implementation (not included in this study). Subsequently, the Jefferson County Flood Board has asked PWA to supplement this study with additional analysis of flood hazard reduction measures upstream. This study is pending. d50 \D: \ERI('A \WORKING \103;FEAS.DO8 et Wp6.1 \9/6i95 IL CONCLUSIONS AND RECOMMENDATIONS A. CONCLUSIONS 1. Fish spawning and usage of the lower Big Quilcene River have adapted to the natural channel form that depends on the continued functioning of key physical processes including occasional large floods, continued coarse sediment transport in to the delta, and the availability of large woody debris in the channel. 2. Human intervention in the watershed and river system over the last century has altered these physical processes directly or indirectly, causing a deterioration in habitat. Of most significance are channelization or confinement of the river channel, dredging and removal of large riparian trees and debris jams. 3. Development has now occurred in the active meander zone of the river channel that is a natural sediment deposition zone and floodplain. This development is vulnerable to flooding and also susceptible to channel migration as the channel bed raises over time. Ensuring that flood hazards and rates of bed deposition are not increased is therefore a key design constraint for the restoration. j4. Four design alternatives were evaluated including the No Action Alternative (Alternative 1), an alternative that lowered the north bank levee below Linger Longer bridge (Alternative 2), an alternative that both lowered the north bank levee and set back the south bank levee below Linger Longer bridge (Alternative 3), and an alternative that also restored habitat values between Rogers Street and Linger Longer bridge by setting back both levees as well as restoring the reach downstream (Alternative 4). Each of the restoration alternatives could be implemented in phases. 5. The restoration alternatives would allow for natural processes to reestablish themselves including channel aggradation, channel migration and the deposition of debris allowing formation of new channels to the north. This would offer significant potential for creating high value spawning habitat. 6. Based on our modeling of flood flows and sediment deposition. none of the restoration alternatives are expected to cause an increase in flood elevation over the long term. In the short term flood levels would likely be reduced. 7. Allowing for natural channel switching below Linger Longer bridge will maintain a steeper channel thereby limiting sedimentation and flood elevations above Linger Longer bridge. #50ADIERICAMORKINGA1033FEAS_1308 et wpo 1A9 /6,95 2 A summary of the comparison of alternatives is shown as Table 1. TABLE 1. Summary of Comparison of Alternatives Alternative Flood Hazard Habitat Relative Costs Flood Resilience to Length of Human Initial Maintenance Elevations Extreme Restored ! Disturbance Floods River (ft) Potential 1 — low 0 very high 1 0 j high 2 no change mod -low 3000 moderate i low I moderate no change mod -high 3000 low moderate I low 4 no change high 4200 low o high ve low rY B. RECOMMENDATIONS Alternative 4 offers the opportunity to restore the highest value spawning and rearing habitat without increasing flood hazards. This alternative allows for a progressive implementation of habitat restoration and concurrent phase out of gravel removal activities. We recommend this alternative should be considered for implementation subject to the availability of adjacent land. 2. If it is infeasible to implement Alternative 4, Alternative 3 should be implemented but with future gravel removal above Linger Longer bridge carried out in a way that reduces impacts to fish habitat. 3. We do not recommend installation of artificial in- channel habitat structures. Instead we recommend monitoring of the evolution of channel form and fish use. if there is insufficient channel complexity after 5 years, in- channel structures could be installed. 4. To minimize habitat disruption there is an advantage to implementing the restoration plan in phases. To minimize disturbance, the downstream reaches should be restored first. 5. As part of the restoration plan, a long term monitoring program should be designed and implemented to assess changes in habitat, fish spawning and flood hazard variables such as channel conveyance and bank erosion. # 50 A13 .AERICAAWOKKINGA1033FGAS.D08 et wp6.1A916/95 6. —A corridor of natural riparian trees should be allowed to grow adjacent to the river, including the section under the power lines. 7. An erosion resistant sill should be maintained on the right bank above Rogers Street; to allow floodwaters to overflow without initiating permanent channel switching. N50 \D \EIUCA \WORKING \1033FEAS.DO8 et p6, 1\9/6/95 4 III. EXISTING CONDITIONS AND PROCESSES A. PHYSICAL 1. Hydrology The Big Quilcene River Restoration site is located on the delta of the Big Quilcene River that drains approximately 69.1 square miles (FEMA, 1982) of steep forested watershed on the eastern slopes of the Olympic Peninsula (Figure 1). Average annual precipitation ranges from approximately 50 inches, near the town of Quilcene and the river mouth, to 76 inches in the upper watershed area south of Mt. Constance (USDA, 1994). Average annual precipitation for the watershed is estimated to be 65 inches (CH2M Hill. 1978). Streamflow gauging along the mainstem of the Big Quilcene River has been intermittent since the 1920s such that there is not enough continuous period of record to permit a statistical analysis of gauged flows. Flows have been gauged at and in the vicinity of the City of Port Townsend diversion dam in 1926 -1927, 1951, 1971 -1972, 1993, and 1994 at approximately river mile 9.4. Because of the lack of gauged data and streamflow statistics. USGS regional regression equations were used to develop streamflow data at the mouth of the river. Mean monthly flows were estimated using regional regression equations based on watershed characteristics at adjacent gauged streams (Collings, 1971). Use of the regression equation for western Washington streams resulted in the mean monthly flow estimates shown in Figure 2. These flows compare favorably with summer low flow estimates at the mouth of 20 cfs and a mean annual flow of 200 cfs. These values also compare reasonably to actual mean monthly flows gauged on the Big Quilcene River during the short periods of record. An error was noted in the 1971 regression relation for estimating September mean monthly flows. This flow was estimated by assuming the September flow was 54 percent of the August, as determined from a review of actual gauged flows for those months during the above mentioned intermittent flow periods of record. Return period peak discharges at the mouth of the Big Quilcene River are published in the 1982 Jefferson County FEMA Flood Insurance Study for the 10 -, 50 -, 100 -, and 500 -year events. These discharges were used to estimate lower frequency peak discharges by extrapolating down to the 5 -, 2 -, and 1 -year events (Figure 3). Engineering studies to define the regulatory floodplain elevations that were published in the 1982 report apparently were completed in the 1970's. Since this date, the removal of the Rogers_Street bridge, channel aggradation from 1971 to 1993 (Collins, 1993), and dredging and river berm constriction using dredge spoils have significantly altered the river channel and flood behavior of 450 VD'.AERICAMORKINGU0I3FEAS_D08 et wpb IA9/6/95 5 the downstream reach river near the mouth. These changes are assumed to have changed the published 100 -year Base Flood Elevations (BFEs). Based on this assumption. new flood elevations for existing conditions have been estimated using updated river cross - section data with the 1982 FEMA return period flood flows based on the HEC -2 model. Figure 4 shows the approximate limit of the 100 -year floodplain that covers the entire alluvial fan. During such an extreme event, the main channel carries only a minor fraction of the total flow. Analysis of the HEC -2 flood model shows that in floods larger than about the 5-year event, significant overbank flooding occurs above the Rogers Street bridge and much of this flow continues across the alluvial fan without reentering the main channel. This limits the amount of flow left in the main channel. In its present state, the main channel has a capacity less than the 5 -year flood above Linger Longer bridge and less than the 2 -year flood below the bridge. 2. Sediment Transport Sediments conveyed by the Big Quilcene River are mainly contributed by landsliding in the watershed. While landsliding occurs naturally, its incidence is greatly increased by the construction of logging roads. Consequently, the amount of sediment contributed to the river during the last a0" years of logging has probably greatly increased, but is now likely declining as the watershed reforests, and roads are restored. A minor additional source of sediments is an eroding gravel bluff on the left bank, about 1.7 miles above the mouth. Most of the sediment is moved by the river only during the larger flood events and is conveyed in two ways: 1) the finer particles, sands and muds that compromise most of the total sediment load, move as suspended load; and 2) the coarser sediments, gravels and boulders, move along the bottom of the channel as bed load. During a typical flood event, most of the suspended load is carried all the way down river and discharged into Quilcene Bay where it is deposited on mudflats and in deeper water. Some of the suspended load is deposited on the floodplain upstream where flood flows overtop the bank. Coarser sands tend to be deposited on the floodplain close to the channel bank — particularly where there is dense riparian vegetation; over time a low natural levee is built up. In this way, a channel can preserve its natural form even when there is long term aggradation of sediment on the channel bed. ( "Aggradation" means sedimentation build -up on the bed.) Bed load is moved during floods whenever the flow exceeds the velocity large enough to start moving individual particles. Cobbles or boulders move downstream intermittently, from bar to bar, and can take several years to move downstream. It is mainly the bedload that forms the substrate 450 AD- \ERICAAWORKINGAI033FEAS.DO8 et wpb. IWW95 6 and structure of the river channel, and this structure, in turn, provides spawning habitat for chum salmon and other species. During the course of a flood as the flow increases. the bed tends to scour deeper, mobilizing more and more coarse bed material. As the flow recedes. bed load is redeposited, reforming the original channel structure. It is during the peak of the floods when the active channel is at its deepest that the most rapid bank erosion tends to occur. $ank_erosion protection- aceds_to..be c-onstructed_deepl�r - than the estimated maximum depth of scour to prevent it from being undercut and failing. Artificial changes in the channel cross - section also affect sediment transport. Where the flow is confined between levees, scouring tends to be deeper and moves the gravel bars more frequently. If large pits are excavated in the channel bed for gravel extraction, most of the bedload and some suspended sediment is captured during flood events until the pits are filled. This interruption of bed load transport causes bed and bank erosion downstream with lowering and widening of the channel. Later, the bed lowering extends upstream above the pit until an even gradient is reestablished. Other forms of gravel removal such as bar scalping or maintenance of gravel "sumps" (smaller pits excavated only on the bars) ultimately have similar effects in lowering the channel bed, except the impacts are more gradual and distributed over a longer reach of river. The role of large infrequent floods is especially important in determining the channel form. It is during these floods that channel switching can occur and in which large trees and other woody debris is moved into the channel. 3. Geomorphic Evolution Since the last Ice Age, sediments eroded from the Big Quilcene watershed have accumulated on the valley floor, building up a relatively flat alluvial floodplain in the lower four miles. Where the river discharges out of its valley, about one mile above the mouth, sediments have formed an alluvial fan across which the main river channel flows. As the river reaches tidal influence in its last quarter mile, the sediments have created a river delta, and in this tidal reach the river tends to split into smaller distributary channels before dissipating in Quilcene Bay (Figure 4). The form of the Big Quilcene's alluvial fan and delta has been created as a result of deposition and channel migration from episodic large floods since the end of the last ice age, and then modified by human activities in the last century. In its natural state, the alluvial fan can be considered to be in a state of dynamic equilibrium (although gradually changing over time). Major changes can occur as a result of large flood flows, but the basic form of the river channel and the alluvial fan maintain themselves over a long period of time. It is this natural form that the salmon have adapted to over time. The key processes that create the natural form are assumed to be as follows. Sediment deposited during flood events tends to build up low natural levees that are about 1 to 2 feet higher than the d50VD TRICAMORKINGA1033FEAS. DOS et wpb. I`9/6/95 7 floodplain and act to contain the river channel. Over time, the channel extends further and further into the bay, until at some point during a large flood log jams occur and /or the natural levee is breached and the river finds a shorter path to the bay, abandoning the old channel. Over a long period of time, successive channel switching occurs that builds up a fan of abandoned channels and floodplain sediments. In its natural state, flood flows on the river would also have conveyed large riparian trees downstream. Sometimes log jams would occur that would block the flow and tend to increase the likelihood of channel switching. On the other hand, dense mature natural vegetation growing on the floodplain would have tended to inhibit the formation of new channels, except in very large floods. The presence of large woody debris in the river channel is important in creating pools, cover and habitat for salmonids. Although major sudden channel changes occurred infrequently, the main channel would also have gradually migrated across the alluvial fan as a result of the natural meandering tendency of a river channel that is inevitably associated with the formation of gravel bars and pools (Figure 6). It is this natural channel migration that creates the complex structure of the river channel that provides for spawning habitat on the bars and deeper shaded habitat below steeply eroding banks. There is another important physical process that creates additional spawning habitats and is unique to alluvial fans like that of the Quilcene that discharge into sheltered estuaries. During floods, floodwaters overtopping the natural levee would flow through the riparian woodland away from the main channel. As this flood water moved downslope, most of the sediment would be captured by the vegetation and eventually relatively clear water would be collected inside channels. These side channels would tend to be scoured rather than filled during floods. Consequently, these side channels also provided suitable habitat for spawning. Over the last century the physical processes that created good salmonid habitat have been altered in the following ways: — Increased Sediment Load Logging in the watershed has significantly increased sediment delivery accelerating sedimentation downstream. Historic changes in bed elevation are shown in Figure S. It appears that sediment delivery is now declining, although aggradation rates are expected to decline, it will probably take a few decades for the coarse sediment to work its way downstream. 00 AD'.AERICAAWORKIAGA1033FEAS_D08 et wpb. 1A9/6/95 8 Channelization and Levee Construction As development occurred on the alluvial fan, the river channel was straightened and artificial "levees" or berms were constructed to contain floodwaters by placing excavated bed sediments on the river bank. Although these levees are not engineered structures and offer protection only against the smaller floods —less than the 5 -year event —they have significantly reduced the frequency of overbank flooding in smaller floods. and by confining floodwaters to the channel tended to increase the frequency and period for which channel bed gravels are mobilized. In addition, by confining sediments to the main channel, the levees have caused the mouth of the river to lengthen over time, making the lower part of the river less hydraulically efficient. This in turn has caused sediment deposition in the channel raising its bed in some locations higher than the adjacent floodplain (see Figure 7). Figure 5 shows how the river delta has changed over time, and illustrates how the main channel has been artificially kept in place over the last 40 years. Figure 5 also shows that the natural sinuosity of the river channel was significantly greater than what now occurs in the channelized reach. Based on a comparison of aerial photographs between 1947 and 1990, the mouth of the delta has advanced about 1,500 feet into the Quilcene Bay. Levee construction and maintenance usually requires access to and disturbance of the river bed, adversely affecting spawning and rearing habitat later in the year. Levee construction has also prevented the scouring and clearing of secondary channels by overbank flows. degrading these channel's habitat value. Gravel Removal Dredging of gravels from the river bed has occurred both for commercial reasons and as a means of lowering the channel bed to reduce flooding. The main methods used have been grading the entire channel bed and excavating in- channel pits that fill with sediment during a flood. These significantly disturb or eliminate the natural structure of the river channel that provides spawning and rearing habitat. Eventually, with successive years' floods, the natural structure reestablishes itself until excavation occurs again. Elimination of Riparian Vegetation Removal of riparian vegetation has had three significant effects on the river. The supply of large woody debris from upstream during floods has been reduced, adversely affecting habitat diversity and tending to reduce the tendency to meander (Abbe and Montgomery, 1995). However, log jams still occur in the lowest part of 950VD:AERICA \WORKINGAI03 ,FEAS.DOB et wpb_ 1A9/6/95 9 the river where tidal influence is significant (Figure 9). Loss of riparian forest makes the river bank more susceptible to erosion, creating a wider shallower channel than would occur naturally. Removal of riparian trees on the alluvial fan. such as has occurred occasionally under the power lines, tends to remove their sediment filtering affect and allowing for faster velocity overbank flows, facilitating channel switching. In addition, loss of riparian trees due to levee maintenance degrades fish habitat by loss of shade and food source. Bridge Construction The construction of Linger Longer Road bridge and the Rogers Street bridge has artificially fixed the lateral migration of the river channel at these two locations. Even though the Rogers Street bridge has now been removed, the road embankment still confines the flow. A significant concern in the short- to mid -term is whether a major flood could initiate a major channel shift. away from its present course, that could adversely affect shell fish habitat, dewater the main river channel temporarily adversely affecting the fish habitat, and increase flood hazards downstream. As can be seen on Figure 11 and Table 2. there are several potential flow paths that now have a steeper gradient than the present river channel. The most serious risk is the potential for a new channel forming on the right bank from above Rogers Street to the Bay because its steep gradient could cause a major realignment of the river corridor. TABLE 2. Potential Impact of Channel Switching Flow Path (see Figure lI) Gradient ft/ft Impact of Switching Shellfish Fish Habitat Habitat Flood Damage Existing River 0.0035 — — — 1 0.0056 Very Severe Very Severe Very Severe 2 0.0036 None i Severe Severe 3 0.0040 ' Nane i I Minimal j Minimal 4 j 0.0050 Severe i i ! Minimal Minimal 5 0.0026 Severe Minimal None 6 0.0014 I None i Minimal None 0.0011 1 None Minimal None 450AD AERICAAWORKINGVI03.WEAS. DOS et wp6.1V9/6/95 10 A key criterion affecting the restoration design is predicting the equilibrium form of the natural channel in the lower river. This can be done by using generic "regime" equations based on correlation of natural channel geometry with bankfull discharge (Emmett, 1975; Bray. 1982); or more accurately. the survey information of the specific natural channel. Fortunately, two cross - sections surveved are available for the lower river from 1972 below the reach that had been leveed at that time. These provide a good indication of the natural channel geometry as shown in Table 3. TABLE 3. Equilibrium Geometry of the Big Quilcene River Source Max Depth (ft) Average Depth (ft) Top Width (ft) Area (ft=) Station 1650 3.9 2.9 67 197 Station 1750 3.4 2.6 65 167 Average 3.7 2.8 66 182 Emmett's Equation — 2.8 63 — Bray's Equation — 2.8 100 i — Of major concern in the management of the river corridor is the rate of aggradation of the river bed. Collins (1993) analyzed historical channel surveys over the period from 1971 to 1993 and estimated the actual sedimentation rate to be about 1.000 cubic yards /mile /year in the lower river, or a rise in thalweg (the deepest part of the channel) elevation of about 2 feet in 22 years. Adding the amount of gravel excavated (about 30,000 cy) increases the sedimentation rate to 2,400 cubic yards /mile /Year, or between 2 and 7 feet of aggradation. However. Collins considers this rate to be anomalously high, probably due to a sediment "pulse" due to watershed logging, and not representative of long term rates. A longer term estimate can be obtained by analysis of the rates of progression of the delta into Quilcene Bay. Figure 5 shows that in the period 1947 -1990 (the period of what appears to be the Greatest watershed disturbance) the mouth of the river advanced about 1,500 feet. Assuming a typical fan slope of 0.0035 indicates a net aggradation rate at the mouth of 0.125 ft/yr. B. ECOLOGIC FUNCTIONS The Big Quilcene River formerly supported an important wild salmon fishery that spawned in the lower 3 miles of river channel. Now, largely because of deterioration in habitat, most of the salmon using the river are produced by the Big Quilcene National Fish Hatchery located 2.7 miles above the 450 \D. \ERICA \%Y0RKING \1033, FEAS. D08 et wpe. 1 \916195 11 river mouth. The main salmon runs have been spring chinook, coho and chum. It appears that wild chinook no longer spawn in the river; coho are considered a depressed stock, entirely dependant on the hatchery; and chum salmon, which would naturally spawn in the lower part of the river, is a mixed wild and hatchery stock (USDA, 1994). There are two runs of chum salmon, the late fall run which is listed as healthy by the Washington Department of Fish and Wildlife, and the early or summer run, which has experienced significant decline in the last decade (Figure 10) and is now listed as a critical stock in danger of extinction (Nehlsen et al., 1991). Chum salmon spawn in fresh water fairly close to the river mouth. They require stable and fairly uniform gravel riffles with adequate water depths and temperatures. These conditions are most often found in the main river channel. but can also occur in secondary and distributary channels that have been scoured of muds. Because flows are lowest in the summer, the summer run is more vulnerable to alterations in the river channel, the river flow, and the condition of the riparian corridor. Summer chum salmon runs on rivers in the rain shadow of the Olympic Mountains are particularly vulnerable because of naturally low summer flows (Figure 2). On the Quilcene River. straightening the river channel and repeated grading of the river bed for ,gravel extraction have disrupted the available spawning habitat. Excessive sedimentation in the last few decades from eroding logged watersheds smothers spawning gravels with muds and silts. In addition, channel dredging tends to make the riffles wider and shallower than might occur naturally making fish passage more difficult. The placement of levees tends to concentrate higher velocity flows within the channel during the smaller, more frequent floods. This means spawning gravels are scoured more frequently, particularly during the early winter when salmon eggs have hatched within the gravel. Summer water supply diversions also appear to have degraded spawning habitat. In addition, a Forest Service stream survey shows that portions of the lower river are deficient in large woody debris and therefore lack habitat diversity and cover (USDA, 1994). Althouah the main focus of this study is the potential for restoring summer chum spawning habitat, restoring or protecting other important ecologic functions are also considered. These are: Facilitating fish passage from the mouth of the river towards the hatchery by elimination of barriers, provision of cover and channel complexity including deep pools. Improving rearing habitat by providing shading, vegetated riparian corridor, and channel complexity. Allowing the possibility of developing wild coho spawning habitat. 450AD ERICAAAF0RKINGA1033FEA5 -D08 et wp6.1A9/6/95 12 Protecting shellfish beds adjacent to the river mouth. (A large oyster hatchery owned by the Coast Oyster Company might have to be relocated if channel switching causes long -term reductions in salinity.) 7#50 \D'. \ERICA \W0RKING \1033FEAS.D08 et wpb, 1\9/6t95 13 IV. GOALS AND OBJECTIVES Clearly articulated goals and objectives are necessary for the success of any habitat restoration project. The goals express the fundamental purposes of the project, and the objectives provide more specific information guiding actions to be taken to meet the goals. Ideally, the project plan and design are developed concurrently with the monitoring program. The project objectives are expressed in terms of attributes of the ecosystem which can be measured by the activities specified in the monitoring program. The goals and objectives of the habitat restoration are: GOAL 1. Restore the physical and ecologic structures and functions in the lower mile of the river and delta to restore and preserve fish spawning and wildlife habitat. Objectives: 1. Restore chum spawning habitat by recreating the complexity and morphology of the natural river channel and delta. ?. Accommodate the natural rate of channel migration and aggradation while protecting the habitat from major sudden vertical and horizontal changes caused by sediment deposition and channel switching. 3. Restore segments of the riparian vegetation corridor to provide benefits for fish spawning and rearing, such as shade. insects and sources of large woody_ debris. 4. Allow for a more natural frequency of overbank flooding on the delta by lowering and/or setting back sections of the levee. 5. Minimize maintenance requirements by removing the threat of flooding and the incentive to remove gravel or vegetation from the riparian system. GOAL 2. Assure that the habitat restoration projects undertaken in compliance with Goal 1 do not increase flood hazards on private property, and wherever possible, provide flood hazard reduction as an additional benefit of the habitat restoration projects. Objectives: 1. Ensure that maximum flood elevations are not increased on adjacent and upstream land parcels with inhabited dwellings. N500 TRICAMORKING \1033F @AS. D08 et wpb. [ \9/6/95 14 2. Ensure that existing bank erosion problems upstream are not increased. 3. Minimize the need for remedial actions by maximizing the resilience of the system to extreme flood events. GOAL 3. Protect commercial shellfish beds south of the river delta from freshwater inundation of sufficient frequency and duration that might adversely affect the shellfish beds. Objectives: Manage or limit the migration of the main river channel into shellfish beds by preserving the south bank levee and reducing potential for levee failure. GOAL 4. Ensure long -term success through a monitoring and maintenance program. Objectives: 1. Articulate the goals and objectives in terms of measurable indicators of the success of the restoration. 2. Design a monitoring program which can reliably and efficiently measure the indicators. 3. Design a maintenance program which uses the data from the monitoring program to determine maintenance activities for habitat enhancement and flood hazard reduction. H50VD:AC•RICAAWORKINGAI033FEAS. D08 et wp6_1A9 /6/95 15 V. OPPORTUNITIES AND CONSTRAINTS A. OPPORTUNITIES • Acquisition of land in the floodplain will allow for the restoration of a more natural evolutionary relationship between the river channel and floodplain. This will improve the potential for restoring self - sustaining fish habitat. • Habitat restoration can reduce flood risks and so reduce the need to intervene in the channel for gravel removal and levee maintenance activities which impact habitat. • Long -term channel maintenance costs can be reduced by reducing the need to intervene in channel processes to achieve flood risk reduction. • Riparian forest restoration can reduce bank erosion by providing natural bank stability, capture sediment by reducing overbank flow velocities, and reduce the frequency of major channel changes. • River restoration will also improve habitat in the floodplain tidal channels used by late chum. • The natural geomorphic evolution of the channel will increase channel complexity and fish spawning and rearing habitat. • The natural tendency of the channel to switch in its lower reach can be used to alleviate future flood hazards upstream. • Shellfish beds can be protected from channel migration without significantly limiting the habitat restoration opportunities B. CONSTRAINTS • The need to protect private property, bridges, and roadways limits allowable water surface flood elevations which might reduce some opportunities for riparian habitat restoration. • Protection of private property adjacent to the river may require bank maintenance which would reduce habitat restoration potential. #50A13 \ERICA \WORKINGAI033FEAS D08 et wpb _1A9 /6/95 16 The need to protect the shellfish beds limits the opportunities for restoring natural channel migration patterns to the south. Lack of up -to -date survey data and base maps and lack of peak flow data makes accurate prediction of the hydraulic characteristics and behavior of the river less reliable. There is a potential for channel switching above the restoration reach that could severely affect habitat values whether or not restoration actions are implemented. 450 \D. \ERICA \WORKING \103 iFEAS. DO8 et wp6.1 \9/6/95 17 VI. DESCRIPTION OF ALTERNATIVES A. NO ACTION ALTERNATIVE (ALTERNATIVE 1) For the purposes of this analysis we have defined the No Action Alternative as the continued management of the river channel to preserve as far as possible its existing configuration, elevation and alignment. This alternative would require frequent channel excavation, debris removal. bank protection and levee repair. It is assumed that the channel and riparian corridor in the future (over the next 30 years) will be maintained in a condition similar to that seen today. Approximately an average of 2000 cubic yards (cy) per year of sediment would have to be excavated from the river bed up to Rogers Street. There have been three methods of gravel removal suggested for the lower river: — Channel Dredging This would excavate the entire river bed to a depth of several feet (as was carried out in 1992). While removal of large amounts of sediment at one time reduces the frequency of gravel removal, the entire channel substrate is disturbed even if a low flow channel is regraded. It can take several years for natural flood flows to reestablish suitable spawning habitat. Until this happens, habitat values are severely degraded. Therefore, this method is not recommended for the lower Big Quilcene. Bar Scalping Requires scraping accumulated gravels off exposed bars above the low flood channel. This reduces the impact on channel structure and water quality, and is often the approved method for permitting agencies. However, there can still be adverse impacts to salmonids (Pauley, et al. 1989). The river channel tends to become shallower and more homogeneous with fewer backwater areas, and bar vegetation is frequently disturbed. Because of the high expected sedimentation rates in the lower Quilcene and the limited area of bars, scalping would probably be required every year to maintain the channel bed elevation. — Bar "Sumps " This is an experimental technique that is a modification of the bar scalping method. It would excavate pits several feet deep in the exposed gravel bars during the low flow period and then later connecting their downstream end to the river channel to provide pool resting and feeding habitat for fish. This has the additional advantages #50\D \ER1CA \W0RKING \IU33FEAS.D08 et wp6 1 \9/6/95 18 of reducing the frequency of gravel removal to about once every 2 to 5 years, and possibly reducing the number of bars affected. The potential drawbacks of this technique are that the sumps could capture fine sediment as well as gravel, making them less efficient, they also could capture the low flow channel through headword erosion, and they might attract spawning redds in a location that could be easily washed out when the rivers rise. For the No Action Alternative, and for maintenance dredging in the restoration alternatives, it is assumed that either bar scalping or bar "sumps" are used. B. RESTORATION ALTERNATIVES (ALTERNATIVES 2, 3 AND 4) The overall strategy in formulating restoration design is to reconfigure the river corridor in a way that would allow for the natural physical processes to reestablish themselves resulting in the evolution of suitable fish spawning habitat. This is done by eliminating or reducing the need for continued management interventions that degrade habitat values. The following approaches are used to eliminate interventions: • Elimination of dredging and gravel extraction: by allowing for greater flood flow conveyance to compensate for channel bed aggradation. This is done either by setting back or lowering levees. • Elimination of channel bank and levee maintenance: by creating a "meander zone" where the channel will be allowed to migrate. through lowering or setting back levees. • Elimination of debris removal in river delta region: by allowing for possible channel switching into natural undeveloped areas at the river mouth during very large floods. Because the emphasis of this restoration strategy is on the natural evolution of the physical processes. it is important to consider how the alternatives would perform over time. Therefore, the alternatives are characterized both by how they would be constructed and by how they would have evolved after 30 years (discussed in the next section). An alternative strategy that would have attempted to create channel habitat through constructing artificial structures within the existing channel alignment was not recommended because the steep river gradient, high flood velocities and wide channels would likely make maintenance prohibitive. Nevertheless, there may be a few locations where channel habitat structures might be beneficial —if appropriate, these locations can be identified after monitoring the evolution of the channel over a period of about ; years. x50AD'VERICAUWORRINGAIW3FEAS D08 et p6 .1A9/6/95 19 The scope of work for this study required assessment of restoration of the river downstream of Rogers Street. However, it is apparent that there are greater land use constraints on restoration on the 1,200 foot reach between Rogers Street and Linger Longer bridge than the 3,000 foot reach downstream. Therefore, alternatives were formulated with and without the Rogers Street - Linger Longer Reach. In addition. restoration of the riparian corridor in this reach was limited to a total width (about 90 feet) necessary to ensure no increase in flood levels. The river below Linger Longer bridge is divided into two reaches to facilitate implementation of the project in phases. The first phase is defined by the river reach already in public ownership at the mouth. Another consideration in formulating the alternatives is the need to set back the right bank levee. The purpose for retaining this levee is to prevent the channel switching or migrating and then discharging near the oyster beds. Therefore, above station 1400 some form of levee needs to be maintained. Two alternatives for doing this are to maintain the existing levee in its present location, or to set back and rebuild the levee to allow for a natural river channel migration and the establishment of a riparian corridor. Figure 12 shows a typical cross - section of the restored river channel. The restoration alternatives were formulated with or without restoration between Rogers Street and Linger Longer bridge, and with and without restoration on the right (south) bank below Linger Longer bridge as shown in Table 4. An alternative that restored habitat below Rogers Street but did not restore the right bank was not considered realistic, and therefore not investigated. Figures 13, 14 and 15 show the restoration alternatives that are summarized below: Alternative 2 Alternative 2 would assume maintenance of existing conditions above Linger Longer bridge (Components 3LA, 3R-A). The left bank levee would be lowered downstream (component 1L and 2L). On the right bank the existing levee would be maintained (components 1 R and 2RB). Alternative 3 This alternative would be the same as Alternative 2, except that the right bank levee would be set back (components IRA and 2RA) to allow greater habitat value and less maintenance requirements. 4500AERICAMORK ING \1033EEAS.D09 et wp6.1 \9/6/95 20 Alternative 4 For this alternative, it is assumed that dredging between Linger Longer bridge and Rogers Street would cease and the existing left and right bank levee would be set back (components 3LB and 'ORB). This set back would allow for up to 3 feet of river bed aggradation over the next 30 years. If an unusual event caused greater aggradation, selected gravel removal would be allowed. Downstream of Linger Longer bridge the left bank levee would be lowered (components 1L and 2L), and the right bank set back (components IRA and 2RA). TABLE 4. Summary of Alternatives The three restoration alternatives are comprised of a combination of restoration components implemented for three reaches of the river. The restoration components are described as follows: Reach I — Station 0 to Approximately 1600 Component 1 L would lower the artificial levee on the left bank between about Station 900 and 1600 to its natural elevation of about 2 feet above the floodplain or 3 feet above the channel bed, whichever is higher, by removing material in 30 foot gaps every hundred feet as shown in Figure 12. This will provide adequate hydraulic conveyance while minimizing excavation and disturbance to the riparian corridor. The remaining levee material would be left to erode naturally and no maintenance would be carried out on the left bank. The remnant levee below Station 900 would be left to erode naturally. Component 1 RA would reconstruct the levee between Station 1400 and 1600 by setting it back 1500 feet, but with the same crest elevation. The levee would be tied into the existing duck pond levee. This set back would allow channel migration to occur inboard of the levee while preventing a new channel forming that might discharge into the oyster beds. Infrequent levee repair may be required Il50 \D'. \ERICA \WORKING \103;FEAS.DOS et wpb. I \9/6195 21 No Action above Linger Longer Restoration Between Rogers Street and Linger Longer Left Bank Alternative 2 Only (IL, 1RB, 2L, 2RB, 3 LA. 3RA) Left Bank and Alternative 3 Alternative 4 Right Bank below (1L, IRA, 2L, 2RA, (1L, IRA, 2L, 2RA, Linger Longer 3LA. 3) RA) 3LB, 3RB) (Reach 1 and 2) The three restoration alternatives are comprised of a combination of restoration components implemented for three reaches of the river. The restoration components are described as follows: Reach I — Station 0 to Approximately 1600 Component 1 L would lower the artificial levee on the left bank between about Station 900 and 1600 to its natural elevation of about 2 feet above the floodplain or 3 feet above the channel bed, whichever is higher, by removing material in 30 foot gaps every hundred feet as shown in Figure 12. This will provide adequate hydraulic conveyance while minimizing excavation and disturbance to the riparian corridor. The remaining levee material would be left to erode naturally and no maintenance would be carried out on the left bank. The remnant levee below Station 900 would be left to erode naturally. Component 1 RA would reconstruct the levee between Station 1400 and 1600 by setting it back 1500 feet, but with the same crest elevation. The levee would be tied into the existing duck pond levee. This set back would allow channel migration to occur inboard of the levee while preventing a new channel forming that might discharge into the oyster beds. Infrequent levee repair may be required Il50 \D'. \ERICA \WORKING \103;FEAS.DOS et wpb. I \9/6195 21 to maintain the integrity of the relocated levee. Below Station 1400 the levee would be abandoned and left to erode. Component 1 RB would maintain the existing right bank levee in its present location requiring more frequent maintenance activities. Reach ? — Between Station 1600 and Linger Longer Bridge (Station 3300) Component 2L would lower the artificial left bank levee in the same way as described in component 1 A, and allow riparian vegetation to grow under the power line. Component 2RA would set back the right bank levee as described for component IRA. Component 2RB would maintain the existing artificial levee on the right bank. More frequent maintenance would be required to repair the levee after erosion damage. Reach 3 — Rogers Street (Station 4500) to Linger Longer Bridge (Station 3300) Component 3LA would maintain the existing right bank artificial levee and require regular gravel removal. Component 3LB would set back the left bank levee approximately 60 feet to the north to allow for increased conveyance and_restoration of a riparian corridor. Approximately 60 feet of the Rogers Street road fill would be lowered to the elevation of the floodplain adjacent to the river. Other high areas in the floodway would be graded lower. Additional culverts would also be installed through the left bank of the Linger Longer Road embankment to lower flood levels upstream. (Grading requirements and culvert size will be determined during the later flood analysis study). Gravel removal would be eliminated unless aggradation exceeds the anticipated rate of sedimentation (3 feet in 30 years). y Component 3RA would maintain the existing left bank levee with channel dredging. Component 3RB would set back the right bank levee by approximately 30 feet to allow for establishment of a riparian buffer zone. d5 0AD:AERICAAW0RKINGA1033FEAS_D08 et wpb. 1A9/6/95 22 VII. ASSESSMENT OF ALTERNATIVES A. GEOMORPHIC EVOLliTION 1. General The future evolution of four important physical characteristics that affect habitat and flood hazards have to be considered. These are: • Channel aggradation; • Channel switching; • Channel form (cross- section); • Channel structure. For the purposes of this feasibility study. it is assumed that the planning horizon is 30 years from the present. Therefore, the expected behavior of each of these processes was analyzed over the next 30 years. 2. Channel Aggradation Channel aggradation can be analyzed in two ways: 1) by modeling the net sediment deposition, and 2) by geomorphic analysis. Because of the complexity of the processes involved. both of these methods rely on some degree of subjective assessment. Deterministic models of erosion and sedimentation in river channels, such as HEC -6, are subject to significant uncertainty, are not considered reliable for Gravel bed rivers, and are only useable where the entire bed is considered mobile. Effectively, this limits its applications to those cases where the flow is confined between levees or river banks. Considerable effort was spent attempting to use HEC -6 with the historical flow sequence to replicate the observed historic sedimentation pattern from 1971 to 1993. However, the model failed to produce the logical pattern of sedimentation actually observed in the river channel for a reasonable range of sediment input variables. Therefore, geomorphic analysis was used to project future aggradation rates. However. an indication of the relative tendency of the bed to scour or aggrade in different reaches is given by the relative velocities predicted by the flood hydraulics model HEC -2. This is shown in Figure 17 and Figure 18 for post construction and future conditions. H5 0 AD' \ERICAAWORKINGA1033 FE.AS.D08 et wpti.lA9 /6/95 23 Geomorphic analysis of aggradation relied on two sources of information: 1) historic rates of aggradation of the lower river channel as indicated by the progression of the Delta, and 2) estimates of bed load accumulation derived from channel survey and gravel extraction records. Even with continued gravel removal in the channel upstream with Alternative 1, the mouth of the river would continue to extend into tidal waters making the gradient more shallow and effectively raising the bed level at the mouth by about 4 feet over 30 years. For other alternatives, aggradation in the lower reach of more than about 2 feet inevitably would cause channel switching and a steepening of the flow gradient. More than this amount of aggradation could occur after a single flood as happened in 1991. Therefore, it is anticipated that channel switching in the lower reach would occur quickly. Estimates of bed load accumulation upstream is based on extrapolation of the past history of aggradation as shown in the surveys of 1971 and 199' ) (see Figure 7). It would be prudent to assume about 2,000 cubic yards per year downstream of Rogers Street. This translates to an average of about 3 feet of aggradation across the entire channel width in the next 30 years within the study reach. This also provides an approximate estimate of the amount of dredging required for Alternative 1, if done with a relatively efficient technique. / For the restoration alternatives, it is assumed that the aggradation would be somewhat less at Linger Longer bridge because of increased velocities at the bridge due to the steepening of the water surface by overbank flow and channel switching downstream. A summary of the potential aggradation rates is shown in Table 5. N50 \D \ERICA \WORKING \1033FEAS.DO8 et p6 1\9/6/95 24 TABLE 5. Potential Channel Aggradation over the next 30 Years Alternative Potential Increase in Anticipated Increase in Bed Elevation (no dredging) Bed Elevation (ft) (ft) Rogers LL Station 330 Rogers LL Station 330 Street Bridge Mouth Street Bridge I Mouth 1 3 3 4' 03 03 4= 3 �� 71 03 *1 21 3 ; 21 21 03 21 2' 4 3 2' 2' 3 ' Assumes channel switching within 30 years '- Based on historic aagradation rates Maintenance dredging assumed 3. Channel Switching Channel switching potential is assessed by analyzing the water surface elevation of the bankfull flood for each of the potential new river channel courses (Table 2). 'When river channel aggradation in the lower reach exceeds about 2 feet, channel switching to the north is highly likely -to occur because the equilibrium channel depth is approximately .33 feet. The river channel is, than. steepened and shortened (Table 3). - Allowing natural channel switching to occur in the lower reach below Linger Longer bridge in the restoration alternative essentially acts as a safety valve, limiting the maximum bed elevation downstream. In other words, if sedimentation or debris obstruction significantly impairs the flow capacity of the channel, it will migrate to a new course, insuring that flood elevations upstream are not significantly affected. It should be noted that unless remedial action is taken there is quite a high chance of a significant switch during a major flood above Rogers Street for all alternatives. 4. Channel Form Where the channel is allowed to develop naturally in the lower reach under the restoration alternatives, it is assumed that within 30 years it will evolve an equilibrium cross - section with natural low levees and mature riparian vegetation similar to the river channel state prior to levee 450 AD'.AERICAMORKINGA1033FEAS_D08 et wp6.1A9/6/95 25 construction. The nature of the cross - section is indicated by the 1972 channel survey in the lower section. and by hydraulic geometry relationships. It is also assumed that this channel will tend to migrate laterally, except where prevented by levee maintenance. For the No Action Alternative and for the reach above Linger Longer bridge, it is assumed that the channel would be artificially maintained close to the present form. 5. Channel Structure We are assuming that a natural channel structure of riffles and pools would reform quickly once interventions are removed. Recognizing that maintenance would be required for some alternatives. Table 6 shows the relative degree of disturbance from maintenance for both levee repair and gravel removal. TABLE 6. Relative Degree of Maintenance Activities Alternative Above Linger Longer Bridge Below Linger Longer Bridge i very high very high 2 very high moderate 3 very high low 4 moderate low B. FLOOD HAZARDS 1. Flood Elevations Flood hazards are analyzed using the HEC -2 model examining flood elevations for each alternative immediately after construction, and after 30 years. For very large floods, such as the 100 -year flood, significant overbank out of channel flooding occurs upstream and because only a fraction remains in the channel, the different channel geometry of different alternatives would have little affect on flood hazards. For the more frequent smaller floods, floodwaters can be contained within the channel and the channel morphology could significantly affect flood elevations. 450 \D TRICAMORKING\1033FEAS.D08 et wp6.l \9 /6/95 26 Figures 16 through 19 show the water surface profiles for the 2- and 10 -year floods, for different alternatives immediately after construction and after 30 years. The flood water surface profiles after 30 years were based on aggradation shown in Table 5. This tends to be conservative in estimating flood elevations as it assumes a more constricted channel than the equilibrium geometry likely to develop (Table 3). It can be seen that the affect of removing the levee below Linger Longer bridge is initially to lower flood elevations. Over time, aggradation in the channel bed would increase flood levels slightly, but because of the ability of the channel to switch into a steeper course in the restored reach, flood levels would always be kept below those of the No Action Alternative. For Alternative 4, the levee setback on the left and right bank is designed to provide increased conveyance to compensate for the loss of channel capacity due to 3 feet of aggradation over 30 years. However, for this wider channel to be hydraulically effective, additional flow capacity is needed at Linger Longer bridge and can be provided by installing culverts through the embankment. These culverts would capture and return floodwater to the channel downstream that would otherwise overflow to the north. Consequently, velocities and flood elevation in the lower river are slightly higher than Alternative 2 or 3. Table 7 and Figure 19 shows the characteristics of the 10 -year flood for each alternative after 30 years. TABLE 7. 10 -year Flood Characteristics after 30 years Section (ft above mouth) 1 (No ! Action) Flood Elevations (ft NGVD) 2 3 4 Average in- Channel Velocities (fps) 1 (No 2 3 4 Action)' 1730 14.0 10.1 10.0 j 12.1 5.1 0.91 0.91 3.9 2975 18? 13.5 13.4 15.7 4.9 0.81 0.9' 3.1 3325 (Linger 19.4 18.7 18.7 18.1 6.3 10.5 10.5 8.9 Longer Road) 4010 22.6 22.6 22.6 21.1 6.5 6.4 6.4 6.8 4660 (Above j 25.3 j 25.3 25.3 25.3 5.3 5.2 5.2 5.3 Rogers Street) f i Average in channel velocities are low because of significant awav from channel flows across the floodplain. 450AD AERIGUWORKINGA1033FEAS. D08 et wp6. 1A9/6/95 27 2. Resilience of the Design to Extreme Events It is important to consider how habitat and flood hazards could be affected by the following events that would occur during extreme floods. Channel Switching Upstream There appears to be a risk of channel switching above Rogers Street for all alternatives that would have serious adverse flood and habitat impacts. This could be prevented by creating an erosion resistant sill at this location that could allow floodwaters to overtop, but prevent, the channel switching. The location and elevation of this sill should be analyzed in the separate flood study. Setting back levees as provided for in Alternative 4 would reduce the potential for channel switching in the reach between Rogers Street and Linger Longer bridge. — Levee Failure Because the levees are not engineered structures. there is a significant risk of levee failure due to erosion from channel migration and overtopping. Levee failure could adversely affect flood hazards and could affect property and the oyster beds. Those alternatives that allow for a natural meander corridor and reconstructed levee (Alternatives 3 and 4) are therefore more resilient. — Debris Obstruction Log jams that back up floodwater and cause bank erosion are most likely to occur close to the river mouth, or at the Linger Longer bridge, but could occur elsewhere. Those alternatives with set back levees (Alternatives 3 and 4) would be more resilient. C. HABITAT The emphasis of the restoration design is to allow the natural evolution of the river channel to create suitable spawning habitat with the minimum of disturbance. There are two main comparative criteria for assessing the habitat quality as summarized in Table 1: Length of River Channel Restored This takes into account the length of channel that could be allowed to naturally evolve suitable structure and where a natural riparian corridor could develop. #50\D. \HRICA \WORKING \I033FHAS. D08 et wp6.1 \9/6195 ?" Degree of Disturbance fi-ona Maintenance Intervention The relative disturbance of spawning and rearing habitat is summarized in Table 6. Other habitat concerns are addressed as follows: — Potential,for Channel Switching Degrading Oyster Habitat All alternatives maintain right bank levees and allow for channel switching to the north away from the oyster beds. — Potential for Channel Switching Adversely Affecting Spawning and Rearing Habitat The restoration plan is designed to allow channel switching in the lower part of the river in a way that a portion of the restored river channel upstream of the switch would not be affected. Over several years it is anticipated that the new channel course would develop a natural channel restructure and good spawning habitat. However. if a channel switch occurred above Rogers Street, the entire restored river channel could be largely dewatered causing a period of several years in which suitable spawning habitat would be degraded. — Potential for Fish Passage Blockage Natural in- channel obstructions allowed for in the restoration alternative would be extremely unlikely to prevent fish passage in a river as large and wide as the Big Quilcene. — In- Channel Debris This is directly related to the length of channel restored and maintenance activities. For the No Action Alternative, frequent maintenance would largely eliminate woody debris. For the restoration alternatives, debris would be allowed to accumulate and only be removed if it threatened the integrity of a levee. Riparian Vegetation The quality of riparian corridor is directly related to the length of channel restored, and to the restoration of a natural flooding and sediment deposition cycle. For the No Action Alternative, it is assumed that frequent bank maintenance activities would result in low quality disturbed riparian habitat. For the restoration alternatives, mature riparian trees would develop wherever the levee is removed or set back. R50VD AERICA \W0R61AGAI03iFEAS. DOS & wp6- 11,9/6/95 29 Scouring oj'Spawning Gravel In an artificially confined channel, higher velocity flows would tend to scour spawning gravels more frequently degrading habitat. Only the No Action Alternative would have a channel that is significantly confined. All of the restoration alternatives would significantly improve spawning habitat proportional to the length of channel restored. Because of the lowered water surface downstream and the constricting effect of the Linger Longer bridge flow, velocities are likely to increase for a few hundred feet upstream of the bridge for Alternatives 2 and 3. This could have a minor adverse affect on spawning immediately above the bridge. D. COSTS 1. Capital Costs The primary capital costs of the restoration alternatives are earth moving, hauling and disposal costs. Table 9 summarizes estimated earth moving volumes for both levee removal and reconstructing levees set back from the channel. If levee removal required double handling. it would be more costly than relocating the right bank levee. Unit costs have not been assigned at this stage. TABLE 9. Capital Cost Factors Levee Removal Levee Set Back Alternative Length Volume Length Volume (ft) (cy) (ft) (cy) 1 0 0 i 0 0 2 2.400 1,000 0 0 3 2,400 1.000 1,900 7.-5 00 4 2,400 1.000 4,300 19,000 2. Maintenance Costs Maintenance costs are primarily gravel removal and secondarily levee repair. Estimated maintenance requirements based on continuing gravel removal and cost per linear foot for levee repair are shown in Table 10. unit costs for maintenance have not been identified at this stage. It K50 \D'. \ERICA\WORK ING %1033EEAS. D08 et wp6.1 \9/6/96 -30 is assumed that levee maintenance for a set back levee is significantly lower than a levee at the river bank and significant maintenance would not be required in the lifetime of the project. TABLE 10. Maintenance Cost Factors Alternative Gravel Removal Levee Repair (cv /vr) Length maintained (ft) 1 2000 8400 2 500 5400 3 500 2400 4 0 0 b50AD'.AERICAAWORKINGA1033FEAS. DOS at po_1A9 /6/95 1 REFERENCES Abbe. T.B. and D.R. Montgomery. Larne woody debris jams, channel hydraulics, and habitat formation in large rivers. Department of Geological Sciences, AJ -20. University of Washington. Seattle. 34 pp. plus figures. Brian Collins & Associates, 1993. Sediment Transport and Deposition in the Lower Big Quilcene River and Evaluation of Planned Gravel Removal for Flood Control. Report prepared for Dungeness - Quilcene Water Resource Pilot Planning Program, Hood Canal Salmon Enhancement Group, and Port Gamble S'Klallam Fisheries Office, 20 pp plus appendices. Bray. D.L. 1982. Regime Equations for Gravel Bed Rivers. In: Gravel Bed Rivers, R.D. Hey, J.C. Bathurst, and C.R. Thorne (eds j, pp. 5 17-580. CH.M HILL. 1978. Engineering calculations of Big Quilcene watershed precipitation. Date stamped 1978. Collings. 1971. Collings, M.R. A proposed streamflow -data program for Washington state, U.S. Geological Survey open file report. 1971. Emmett. W., 1975. The channels and waters of the Upper Salmon River area, Idaho. U S Geological Survey Professional Paper 870 -A, 116 pp. FETMA. 1982. Federal Emergency Management Agency, Flood Insurance Study. Jefferson County. Washington, unincorporated areas. January 19, 1982. Pauley, et al.. 1989. Evaluation of the effects of gravel bar scalping on juvenile salmonids in the Puyallup River drainage. University of Washington, Coop Fisheries Research ]Unit. March 1989. USDA, 1994. Big Quilcene watershed analysis: An ecological report at the %watershed level. Draft report, October 7, 1994. 450\D AERICAAVV0RKINGA103JpEAS_D08 e1 wpo 1A9 /6/45 -�2 FIGURES +At�U `fiRIC:\ \ \YORKI \G \I0?3F[AS. DUX. et wpb.1 \`7/(;;1)5 00 i J� _ U W? r06 —7 --7 8 • • Ivo ti cl moon® ---------- I M m (puoogS �,Pd iQo_q oiqnD) 30-dVHDSICI ti cl it CC it rao /00(, C), Al I 0 e Z Q 1010 0 .0 a .2w figure 5 Geomorphic Evolution of Delta KEY 1883 1947 1990 N figure 6 Natural Channel Structure P, POP B� 4 Philip Williams & Associates, Ltd. 't , T t C` 4 Philip Williams & Associates, Ltd. figure % Channel Profile 30. – – Top of levee (typical elevation) I— Roodplain elevation !— Thalweg (channel bottom) 25'- �••� / C 20'I' > z�`�• - - - - -� i 15 �7 i w 10'- J 1 • dO 57 - --� _ o 0. 0 1000 2000 3000 4000 5000 6000 Distance from mouth (feet) Source: Jefferson County surveys, 1972 and 1995 Philip Williams & Associates, Ltd. figure 8 Historic Profile Change Source: Brian Collin & Associates, Seattle; July, 1993 P LU to LL I w w J Q in JJz EU w > 0 M a z 0 a w uU BIG QUILCENE CHANNEL -BED PROFILE On 20 10 raw 0.0 ---o- -- 71 thalweg - --+--- 93 thalweg ' y ono s. O N I i 4 Philip Williams & Associates, Ltd. 0.5 RIVER MILE 1.0 ON cJ I E figure 10 Peak Count of Early Chum Salmon per Mile in the Quilcene River from 1959 to 1991 Source: WDF Spawning Surveys io0o i Isoo 1600 J 1400 1200 `i 1000 c !too 600 aao .00 0 Y 04 Philip Williams & Associates, Ltd. 11 z/ wj .� '7S V y 0O Z 12 0O to figure 12 Typical Cross Section in Lower River Existing Conditions Proposed Conditions lowerto grade to typical set back levee 2 fnnt hioh floodnlain elevation annroximately 150' 4 Philip Williams & Associates, Ltd. I I 4, Wl o. 4! PROU m2uo-I m5ul—I —9 t-- 0 u Z 'o `2 45 --- ------------ - e OF is I ti 51 P. peo-d 1Qjuo-j M&II-I lam t 4e QA .4" � IQ if 01 —;t C'. ti W-In cc O < in F I:,- I < CJC C) w .0 go ) t Q ol Pleox jasuoj M-SU17 SID;jO-d —9 L- C� 6 z o 7 %0 Q 63 w --d .26 N La figure 16 2 -Year Flood Water Surface Profile Post Construction 25 20 0 C7 Z 15 a� a� c 0 10 W 5 n 2 -year Flood Water Surface Profile Post Construction a� aD a � ao a .j ./ J. mgr Thaiweg Alternative 1 Alternative 2 — - Alternative 3 j Alternative 4 V JVV IVVV IG7UV LVUU GJUU JUUU JJUU 4000 '+JUU JVVV Distance from mouth (feet) 14 Philip Williams & Associates, Ltd. figure 1% 2 -Year Flood Water Surface Profile After 30 Years 2° 2C 0 c� Z 15 a� m C 0 a>10 W 5 w 2 -year Flood Water Surface Profile after 30 years L Q L a • d ♦ �i ♦ ♦ ♦ d ♦ � -yMr Original Thalweg Alternative 1 Alternative 2 -Alternative 3 — Alternative 4 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Distance from mouth (feet) 14 Philip Williams & Associates, Ltd. figure 18 10 -Year Flood Water Surface Profile Post Construction 2° 20 0 -615 X C 0 CU X10 w 5 n 10 -year Flood Water Surface Profile Post Construction V 4� laQ� � W Oq 0 J w 6. t'4 P� 0- Tkw,r- Thalweg - - Alternative 1 Alternative 2 Alternative 3 Alternative 4 v VVV ivvV IJVV GVVV GJVV JVVV JJVV '!VVV YJVV JVVV Distance from mouth (feet) 4 Philip Williams & Associates, Ltd. figure 19 10 -Year Flood Water Surface Profile After 30 Years 2° 2C 0 C z Z15 CD C 0 X10 w 5 10 -year Flood Water Surface Profile after 30 years i 6. aD 0 �a c a i 0 dP Ni ce r ii 00 L , � mr- Original Thalweg Alternative 1 Alternative 2 -Alternative 3 Alternative 4 I 0 500 1000 1500 2000 2500 3000 3500 Distance from mouth (feet) 4 Philip Williams & Associates, Ltd. 4000 4500 5000