4. FISH PASSAGE CONCEPTS

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1 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 4. FISH PASSAGE CONCEPTS Fish passage could be improved by rehabilitating the existing fish passage, constructing a new pipe fish passage, or constructing a rail bridge. These alternatives are compared in Table 4-1 (page 4-3) and described in detail below. Appendix E evaluates fish passage issues for the pipe and rail bridge alternatives. Appendix D provides detailed cost estimates for design, permitting, BNSF coordination, construction, and other items. Costs noted below include all of these project elements. Table 3-1 summarizes project costs and provides a comprehensive cost for three potential restoration alternatives. Improving anadromous fish access to Titlow Lagoon depends primarily on increasing the size of the connection from the lagoon to Puget Sound and lowering the intertidal elevation of the connection to the degree practicable. The existing partially closed pipe opening on the Puget Sound end, together with a 4-foot diameter, severely limits the access opportunity for young salmonids migrating along this shoreline. Enlarging both the opening and the connecting channel (pipe) would make the migration route substantially more attractive. Lowering the bottom of the connection would increase the amount of time this migration pathway is available to the young salmonids during each tidal cycle. 4.1 REHABILITATION OF EXISTING FISH PASSAGE Obtaining grant funding and coordinating with BNSF, as well as completing engineering design, for a pipe passage or rail bridge could be a lengthy process. As an interim measure, the existing 4- foot-diameter outlet pipe from the lagoon could be restored to provide improved potential use by juvenile salmon. Restoration actions would include (see Figure 4-1 on page 4-5): Construction of a small rock groin between the lagoon outlet pipe and the City of Tacoma stormwater pipe. Placing beach fill north of the groin at the discharge point of the lagoon outlet pipe to provide a more natural channel entrance into the pipe. Currently, there is a substantial elevation drop over riprap at the pipe outlet. Flushing the outlet pipe to remove accumulated sediments. The estimated cost to rehabilitate the existing lagoon outlet is $40,000. This cost does not include lagoon dredging or other habitat improvements. 4.2 PIPE FISH PASSAGE Replacement of the existing 4-foot-diameter outlet pipe under the rail embankment with an 8-foot-diameter pipe would provide improved fish passage. Figures 4-2, 4-3, and 4-4 (pages 4-7, 4-9, and 4-11, respectively) provide an aerial photograph overlay, plan view, and cross-section of the pipe concept. The location for the pipe fish passage is just north of the existing lagoon outlet pipe. Installing the pipe further to the south would conflict with the existing 42-inch-diameter City of Tacoma storm drain pipe. An 8-foot-diameter pipe would provide substantial improvement for passage of juvenile salmon compared to the existing 4-foot-diameter pipe. However, the magnitude of the improvement cannot be quantified. Table 4-1 (page 4-3) summarizes key design criteria for the pipe concept. The elevation of the bottom of the pipe fish passage was set slightly below the existing beach grade. If the pipe was set at a substantially lower elevation, it is anticipated that sand and gravel from the beach would eventually fill the pipe to the existing beach grade. The estimated cost to implement this pipe concept is $1.1 million, including design, permitting, construction, and construction management, but excluding BNSF fees, which cannot be estimated. This cost does not include lagoon dredging or other habitat improvements. January (01/0202) 4-1

2 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group BNSF design standards require that culverts installed under rail lines extend at least 45 feet beyond the centerline of the nearest track. This can be accomplished on the lagoon side of the lines, and puts the end of the pipe at approximately the same location as the existing lagoon outlet pipe. However, on the Narrows side, meeting this design requirement would require extending the pipe approximately 20 feet beyond the existing revetment, which is not practical. Requesting a variance from BNSF is recommended. However, obtaining approval of a variance from BNSF can be challenging. Table 4-2 (page 4-4) summarizes results of hydraulic analysis of the pipe fish passage, including potential flooding (see Section 5 for more details) and predicted maximum flow rates and velocities. It is estimated that at times of substantial tidal exchange between the Narrows and the lagoon, water velocities in the pipe could occasionally reach 5 to 6 feet per second (fps), which is sufficient to erode sand and gravel, and even cobbles. The bottom of the pipe could be left bare to provide a larger opening for fish at a lower tide elevation, or covered with a 12- to 18-inch-deep layer of cobbles and gravel to create a more natural channel bottom. The pipe could be installed through the rail line embankment by several methods, including jack and bore, pipe ramming, and microtunneling. Pipe ramming is recommended, which is accomplished by using hydraulic jacks to ram the pipe through the soil. Soil inside the pipe is removed after the pipe is fully rammed into place. With the jack and bore process, soil is removed from the pipe interior as the pipe is rammed through the soil, which can increase the potential for settlement during pipe installation. The GPR study completed at the site indicated a wood trestle may be buried in the rail embankment, which may preclude installation of a pipe by ramming or jack and bore. Additional geotechnical investigation would be required to assess the feasibility of pipe installation. The final pipe installation method would be confirmed during final design following completion of geotechnical investigations and coordination with BNSF. Microtunneling is a lower cost process for long bores, but is not cost effective for short bores. An 8-foot-diameter pipe is recommended as the maximum diameter pipe that can reasonably be installed. Although pipes up to 12 feet or larger can be installed by the ramming method, a general rule of thumb is that it is desirable to maintain approximately one pipe diameter of depth below a structure when ramming a pipe. An 8-foot-diameter pipe achieves this goal. Increasing the pipe diameter to 12 feet would reduce the cover soil depth to approximately one-half pipe diameter, which has a much higher potential to damage the rail lines during the installation process. A steel or concrete pipe would be installed. Steel is preferred as a stronger (and smaller) pipe for easier installation, but would be subject to long-term corrosion. Corrosion can be minimized by installation of a corrosion protection system that uses a sacrificial anode that gradually dissolves and must be periodically replaced. Anodes are typically zinc, but aluminum anodes are also available. Concrete is an option that would have the benefit of improved corrosion resistance and no sacrificial anode is needed; however, a concrete pipe would have an 8-inch-wall thickness versus 1 inch for the steel pipe, which would increase the pipe installation cost. Also, a concrete pipe would not be as strong or durable as a steel pipe. The cost estimate included in this study assumes steel pipe. The final pipe material would be confirmed during final design following completion of geotechnical investigations and coordination with BNSF. To install the pipe, small cofferdams formed from sheet piles would be installed on the beach (in a cell approximately 10 feet long by 20 feet wide) and in the lagoon (in a cell approximately 40 feet long by 20 feet wide). The lagoon outlet pipe would be plugged, and the lagoon would be pumped dry. Water flowing into the cofferdams and lagoon would be pumped continuously for the duration of the construction, and discharged to the Tacoma Narrows. 4-2 January (01/0202)

3 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group Table 4-1. Key Design Criteria for Fish Passage Alternatives Alternative Location Shape and Dimensions Existing Pipe N/A Round. 48-in. dia. (field verified). New Pipe Fish Passage New Rail Bridge (40-foot span), with Pedestrian underpass a Approximately 10 to 20 feet north of existing pipe. Area south of existing pipe is blocked by existing storm drain. Near existing pipe Round. 8-ft. dia. Natural channel, 30 ft. wide Track elevation is approx to 15.0 feet NGVD29 [ feet MLLW]. Lagoon Inlet IE feet NGVD29 [feet MLLW] Beach Outlet IE feet NGVD29 [feet MLLW] Length (feet) Track Elevation a feet [cover depth, feet] 0.26 [6.56] [4.16] 102 Approximately 11 feet Pipe: -3.0 [3.6] Channel: -2.0 [3.6] Pipe: -4.0 [2.6] Channel: -3.0 [3.6] 92 Approximately 9 feet Channel: -2.5 [4.1] Channel: -2.0 [4.6] 4,032 N/A January (01/0202) 4-3

4 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group Condition EXTREME HIGH TIDE Table 4-2. Summary of Preliminary Hydraulic Analyses Titlow Lagoon Restoration Feasibility Study Fish Passage Maximum Tide Height (feet NGVD29) Maximum Tide Height (feet MLLW) Maximum Stormwater Flow Rate (cfs) (see Note a ) Maximum Predicted Lagoon Elevation (feet NGVD29) Maximum Predicted Lagoon Elevation (feet MLLW) Maximum Predicted Flow Rate (cfs) Maximum Velocity (fps) Comment No Stormwater Input Rail Bridge Will occur annually. No Stormwater Input Pipe Will occur annually. 10-Year Storm Event b Pipe Low probability event. 100-Year Storm Event b Pipe Extremely low probability event. EXTREME HIGH TIDE INCLUDING STORM SURGE c No Stormwater Input Pipe Rare, but historically observed. a b c Predicted storm event flow rates are based on simplified stormwater modeling that likely over-predicts actual stormwater flow rates into the lagoon. Analyses assume the peak flow rate of the 24-hour storm event occurs simultaneously with the annual maximum tide elevation, and assumes that the entire discharge of stormwater from the contributing western Tacoma basin discharges to the lagoon, whereas only 10 percent of the stormwater flow is estimated to discharge to the lagoon. Includes storm surge of 2.4 feet based on historical data. 4-4 January (01/0202)

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13 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 4.3 RAIL BRIDGE FISH PASSAGE Replacement of the existing 4-foot-diameter outlet pipe under the rail embankment with a rail bridge approximately 40 feet wide would provide for a very high quality fish passage. Figures 4-5, 4-6, 4-7, and 4-8 (pages 4-15, 4-17, 4-19, and 4-21, respectively) provide an aerial photograph overlay, plan view, and two cross-sections of the rail bridge concept. The location for the rail bridge is set just south of the location of the existing lagoon outlet pipe and City of Tacoma storm drain. Locating the bridge to the south would conflict with the storm drain if left in place. Locating the bridge further north is undesirable, due to the rising grade of the north beach. Placing the bridge as shown in Figure 4-5 means that the existing 42-inch-diameter City of Tacoma storm drain would need to be modified to either 1) discharge into the lagoon, which could be difficult to permit, or 2) run through the opening under the bridge. The design assumes the latter option. The existing storm drain pipe under the rail line, and the storm drain manhole near the existing lagoon outlet structure, would be plugged. Table 4-1 summarizes key data for this concept. The estimated cost to implement this concept is $3.0 million, including design, permitting, construction, and construction management, but excluding BNSF fees, which cannot be estimated. This cost does not include lagoon dredging or other habitat improvements. This alternative includes a pedestrian underpass under the rail bridge for improved access to the beach by park users. The pedestrian walkway has an elevation of +4.0 feet NGVD29 (+10.6 feet MLLW). This is above mean tide level and would allow use during approximately 60 percent of the tidal cycle. However, the beach at this location is lower, approximately -1 foot NGVD29 (5.6 feet MLLW) and is only above the tide line approximately 40 percent of the tidal cycle. Due to the large opening created by the rail bridge, water velocities in the opening would remain below 2 to 3 fps, which would allow for maintaining a sand and gravel natural channel without substantial risk of erosion. While still a constrained channel, the opening would provide for more natural flow characteristics and sediment transport than a pipe. To minimize outage to the BNSF rail lines, the rail bridge would be constructed as follows: Install soldier piles at the ends of the proposed bridge, between and adjacent to the rail lines. Construct concrete panels between the soldier piles in slots excavated under the rail lines. Construct and assemble the bridge components to the extent practical adjacent to the rail lines. Take the rail lines out of service, remove the rails, excavate the channel, install the bridge, and restore the rail lines. Using accelerated bridge construction techniques, it is estimated that the rail lines would be out of service for approximately 48 hours. Construct the pedestrian access, natural channel, and other features. Install the pedestrian bridges adjacent to the rail lines. The bridge configuration, method of installation, and duration of rail outage time would be confirmed during final design following completion of geotechnical investigations and coordination with BNSF. January (01/0202) 4-13

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23 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 5. FLOOD POTENTIAL ANALYSIS Currently, due to the connection of the lagoon to the Narrows, the Federal Emergency Management Agency (FEMA) flood map indicates that the lagoon area of Titlow Park below elevation +9 feet NGVD29 [+15.6 feet MLLW] lies within the 100-year flood plain (see Figure 5-1). These elevations represent approximately the high tide elevation. It could not be determined if FEMA or any other entity had completed a detailed hydrologic/hydraulic analysis to accurately identify the flooding potential around the lagoon. The lagoon lies within the 310-acre Western Slopes 04 drainage basin that drains Tacoma west of Jackson Avenue between (approximately) 6th Avenue and South 19th Street. Most stormwater runoff from this basin discharges to the Narrows through a large City of Tacoma storm drain that lies directly adjacent to the lagoon outlet pipe. An additional stormwater outfall pipe is present near Steamers restaurant. Smaller drain lines empty directly into the lagoon. Due to interties within the storm drain system, it cannot be readily determined how much flow routes to each discharge point. However, it is estimated that 70 percent of the flow discharges through the outfall near the lagoon, 20 percent discharges at Steamers, and 10 percent (most likely less) Figure 5-1. FEMA Flood Map for Titlow Lagoon discharges directly into the lagoon. Several springs discharge directly into the lagoon, including the recently daylighted Crystal Springs Creek at the southeast corner of the lagoon. These springs provide a flow of perhaps 10 to 20 cubic feet per second (cfs) of freshwater flow into the lagoon. The potential for the fish passage to increase inland flooding around the lagoon was analyzed, and results of the analysis are provided in Table 4-2. Detailed calculations are presented in Appendix F. The analysis evaluated a peak high tide event (without storm surge) and 1) no stormwater discharge, and 2) stormwater discharge to the lagoon for the 10- and 100-year storm events. To be conservative, it was assumed that the peak of the high tide coincided with the peak flow of the 24-hour storm event hydrograph, which is a very low probability event. The analysis also evaluated an extreme high tide event including storm surge, but with no stormwater discharge. The key conclusions from the analysis were: With either the rail bridge or the 8-foot-pipe fish passage, the water levels in the lagoon will very closely match the water level in the Narrows. This was the case historically in the 1920s when the lagoon was connected to the Narrows via the Trestle; however, after closure of the lagoon in the early 1930s, the 4-foot-diameter outlet pipe has reduced inflow to the lagoon such that peak lagoon water levels have been attenuated and peak flooding events do not occur. As noted in Section 1.2, the sea level in Puget Sound has risen 0.5 foot since the 1930s, and further rise is predicted. January (01/0202) 5-1

24 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group The water level in the lagoon is: Very likely to reach an elevation of 7.9 feet NGVD29 (14.6 feet MLLW) on an annual basis. Unlikely to exceed 8.9 feet NGVD29 (15.5 feet MLLW) under the combined influence of normal predicted tide elevations and 10- to 100-year storm events (see Figure 5-2). Water level in the lagoon could rise as high as 10.2 feet NGVD29 (16.8 feet MLLW) under extreme tide conditions affected by storm surge. The occurrence of storm surge is a low probability event. However, peak tide elevations, including storm surge, are based on historical observations rather than theoretical predictions. Any extreme water level events in the lagoon will be of short duration (2 to 3 hours), although saltwater inundation may adversely affect vegetation and infrastructure. 5-2 January (01/0202)

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27 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 6. RECOMMENDED ADDITIONAL STUDIES The following additional studies are recommended for final design of the project: Collect a PSDDA characterization of lagoon sediments. Complete geotechnical borings in the area of the proposed fish passage structure. January (01/0202) 6-1

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29 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 7. REFERENCES Mote, Philip, A. Petersen, S. Reeder, H. Shipman, and L. Binder Sea level rise in the coastal waters of Washington State. University of Washington Climate Impacts Group and Washington Department of Ecology. Seattle and Olympia, WA. WSDOT Rail Tacoma Bypass of Point Defiance. Accessed November 17, January (01/0202) 7-1

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