Feasibility Study for Restoration of Titlow Lagoon Fish Passage. South Puget Sound Salmon Enhancement Group

Transcription

1 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group January 2010

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3 Feasibility Study for Restoration of Titlow Lagoon Fish Passage Prepared for South Puget Sound Salmon Enhancement Group 6700 Martin Way East, Suite 112 Olympia, WA Prepared by Parametrix 1231 Fryar Avenue Sumner, WA T F January (01/0202)

4 CITATION Parametrix Feasibility Study for Restoration of Titlow Lagoon Fish Passage. Prepared by Parametrix, Sumner, Washington. January 2010.

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7 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group TABLE OF CONTENTS 1. INTRODUCTION LAGOON HISTORY LAGOON TIDES AND SEA LEVEL RISE LAGOON SEDIMENT BEACH PROCESSES AND GEOMORPHOLOGY BURLINGTON NORTHERN SANTA FE (BNSF) RAIL LINES RAIL EMBANKMENT GROUND PENETRATING RADAR INVESTIGATION MASTER PLANNING AND SELECTED CONCEPTS FOR TITLOW PARK MARINE HABITAT RESTORATION BEACH RESTORATION LAGOON RESTORATION Lower Lagoon Dredging Upper/Lower Lagoon Reconnection FISH PASSAGE CONCEPTS REHABILITATION OF EXISTING FISH PASSAGE PIPE FISH PASSAGE RAIL BRIDGE FISH PASSAGE FLOOD POTENTIAL ANALYSIS RECOMMENDED ADDITIONAL STUDIES REFERENCES LIST OF FIGURES 1-1 Titlow Lagoon as Shown in 1905 Nautical Chart Titlow Lagoon Aerial Photograph from 1931 Showing Lagoon and Beach Geomorphology and Rail Trestle Titlow Lagoon Historic Photograph From 1927 Showing Rail Trestle and Wood Bulkhead in Lagoon Existing Lagoon Outlet Pipe and Adjacent City of Tacoma Stormwater Outfall Site Location Map Titlow Park Site Aerial Photo (2008) Titlow Park Beach Restoration Concept Titlow Park January (01/0202) i

8 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group TABLE OF CONTENTS (CONTINUED) 3-2 Lagoon Restoration Concept Titlow Park Lagoon Dredging Titlow Park Lower/Upper Lagoon Channel Reconnection Titlow Park Restoration of Existing Fish Passage Titlow Park Foot-Diameter Pipe Fish Passage Titlow Lagoon Park Foot-Diameter Pipe (Jack and Bore) Titlow Park Foot-Diameter Pipe Fish Passage Titlow Park Rail Bridge Fish Passage Concept Titlow Park Rail Bridge Water Channel Titlow Park Cross Section: Rail Bridge with Pedestrian Underpass Titlow Park (Section B-B) Cross Section: Rail Bridge with Pedestrian Underpass Titlow Park (Section C-C) FEMA Flood Map for Titlow Lagoon Range of Predicted Lagoon Flood Impacts Titlow Park LIST OF TABLES 1-1 Tide Elevations at Titlow Park (2009) Summary and Compilation of Estimated Project Costs Key Design Criteria for Fish Passage Alternatives Summary of Preliminary Hydraulic Analyses Titlow Lagoon Restoration Feasibility Study APPENDICES A B C D E F Tide and Sea Level Rise Analysis Geomorphology and Beach Process Evaluation Ground Penetrating Radar Study Cost Analyses Fish Passage Analyses Stormwater and Hydraulic Analyses ii January (01/0202)

9 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group KEY TERMS BNSF cfs cy FEMA fps GPR MHHW MLLW NOAA PSDDA Burlington Northern Santa Fe cubic foot per second cubic yards Federal Emergency Management Agency feet per second ground penetrating radar Mean Higher High Water Mean Lower Low Water National Oceanic Atmospheric Administration Puget Sound Dredged Disposal Analysis January (01/0202) iii

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11 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 1. INTRODUCTION Restoring Titlow Lagoon will aid salmon by reversing nearly a century of incremental lagoon improvements. Restoring a fish passage from the Tacoma Narrows to the Titlow Lagoon would aid juvenile salmon by providing brackish slack-water habitat in an area of Puget Sound where little exists today. The existing lagoon outlet pipe (approximately 4 feet in diameter by 100 feet long) is too small and dark to provide an effective fish passage. Parametrix was requested to provide a Feasibility Study to identify a preferred restoration concept and estimated cost to aid in securing additional grant funding and to advance the project into permitting, design, and construction. 1.1 LAGOON HISTORY Historically, the lagoon site was an interesting and complex pocket estuary with a sediment sill, mudflats, salt marshes, and numerous freshwater inputs (see Figure 1-1). Construction of the rail line embankment across the entrance to the lagoon in the 1920s was the first of a series of changes that severed the lagoon from the Puget Sound, filled the fringes of the lagoon, and straightened and armored the banks of the lagoon. The original rail embankment featured a wood trestle approximately 150 feet long to maintain a connection to the lagoon (see Figure 1-2 and Figure 1-3). However, the trestle was replaced with an earth embankment sometime in the 1930s. It is not known if the trestle was demolished or left in place. Figure 1-1. Titlow Lagoon as Shown in 1905 Nautical Chart Figure 1-2. Titlow Lagoon Aerial Photograph from 1931 Showing Lagoon and Beach Geomorphology and Rail Trestle Figure 1-3. Titlow Lagoon Historic Photograph From 1927 Showing Rail Trestle and Wood Bulkhead in Lagoon (Used with permission: Tacoma Public Library, BOLAND-B16959) January (01/0202) 1-1

12 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group For the lagoon outlet, the City of Tacoma engineering drawings from 1929 called for installation of a 72-inch outfall and removal of the wood trestle. Apparently, this pipe was not constructed. Later drawings indicated that a 48-inch pipe with earth fill was to be placed around the trestle. Drawings from 1953 show two existing 48-inch culverts, one of which was converted to stormwater discharge at that time. Figure 1-4 shows the two existing outlet pipes. Based on observation, the lagoon outlet pipe is approximately half full with sediment. The pipe is in a deteriorated condition, but not collapsed. A current site location map and recent aerial photograph of the lagoon are provided in Figures 1-5 and 1-6, respectively. Figure 1-4. Existing Lagoon Outlet Pipe and Adjacent City of Tacoma Stormwater Outfall 1.2 LAGOON TIDES AND SEA LEVEL RISE Appendix A presents a detailed analysis of tide elevations in the Tacoma Narrows and an estimate of future sea level rise. The site base map drawings completed by AHBL provide topographic contours in feet, NGVD29 datum. At the Titlow Park site, NGVD29 datum can be converted to Mean Lower Low Water (MLLW) datum by adding 6.60 feet. Note that NGVD29 datum is constant between different locations, whereas the tidal datum varies by location because the tidal range increases moving further into Puget Sound. Table 1-1 compares site elevations in the two primary site datums. Tide Level Table 1-1. Tide Elevations at Titlow Park (2009) Elevation (Feet, MLLW Datum) Elevation (Feet, NGVD29 Datum) Extreme High Tide (includes storm surge based on historic measured values) High Tide (excluding storm surge) Mean Higher High Water (MHHW) Mean Tide Level Mean Lower Low Water (MLLW) Based on Seattle records, sea-level rise from 1930 to 2009 was 0.53 foot (Mote et al. 2008). Predicted future sea-level rise in Puget Sound, based on the medium projection by the Climate Impacts Group from the University of Washington, for 25, 50, and 90 years is 0.3, 0.6, and 1.1 feet, respectively. Prior literature has reported that post-glacial rebound is occurring in Puget Sound and would negate concerns about sea-level rise. More recent literature has noted that land rise or subsidence varies widely with location. The northern Puget Sound is believed to be experiencing rising land surfaces, where southern Puget Sound is, in general, holding steady or subsiding. Specific conclusions regarding land rise or subsidence at Titlow Park are beyond the scope of this study. 1-2 January (01/0202)

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15 Parametrix DATE: Dec 01, N 200 SCALE IN FEET Figure 1-6 Site Aerial Photo (2008) Titlow Park Tacoma, Washington

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17 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 1.3 LAGOON SEDIMENT Due to budget limitations, no sediment samples (either grabs or cores) were collected from the lagoon. A Parametrix engineer walked a portion of the lagoon at low water and observed that lagoon sediments are generally firm and comprised of silt and sand with a substantial fraction of small gravel. 1.4 BEACH PROCESSES AND GEOMORPHOLOGY Appendix B provides a detailed evaluation of site geomorphology. Longshore drift of sediment in this area is predominantly to the north. A site visit, and review of historical aerial photographs of the site (see Figures 1-2 and 1-6), indicate that the beach north of the lagoon has been wider, with more abundant sand and gravel, than the beach in front of or south of the lagoon opening. The beach north of the lagoon is backed by eroding bluffs that directly nourish the beach, resulting in a sand and gravel substrate that is generally considered to be good habitat. In the lagoon area, the rail embankment is revetted with stone to prevent erosion by storm waves, and this stone both prevents direct beach nourishment and reflects waves in a manner that causes beach erosion. Along the rail embankment, the beach thins from south to north, becoming thinnest at the point where the City s large stormwater outfall and the lagoon outlet pipe discharge onto the beach. The nearest source of beach sediment occurs well to the south of Titlow Park, and much of this sediment is lost offshore as it travels northward. As a result, the beach along the rail embankment between Steamers Restaurant and the lagoon outlet tends to be comprised of rock rubble and gravel. Some sediment is transported to the north or south past the lagoon, and the outflow of stormwater and the discharge from the lagoon tend to move this sediment seaward rather than allowing substantial migration to the north or south. A lower intertidal/subtidal sediment delta offshore of these outfalls is visible at low tides and shown in the site aerial photographs (see Figure 1-6). 1.5 BURLINGTON NORTHERN SANTA FE (BNSF) RAIL LINES The twin BNSF rail lines on the embankment are high-speed main line tracks that carry substantial traffic volumes. BNSF has expressed concern regarding any interruption in service. Currently, there is no freight service alternate route for these rail lines. However, BNSF is currently upgrading a rail line between Tacoma and Lakewood to provide for a high speed bypass of the Point Defiance tracks. This line could conceivably be used temporarily as an alternate route for freight traffic. Project completion is reported to be between 2012 and 2019, depending upon funding (WSDOT 2009). Reportedly, the rail lines at this location are closer together, by several feet, than allowed by current design guidelines. 1.6 RAIL EMBANKMENT GROUND PENETRATING RADAR INVESTIGATION Parametrix retained Geo-Recon to complete a ground penetrating radar (GPR) study of the rail embankment fronting the lagoon. The goal of the investigation was to identify subsurface conditions that might affect construction of the proposed fish passage structure. The GPR study was completed in lieu of geotechnical borings because of broader coverage and lower cost. Geotechnical borings to confirm subsurface conditions will be required prior to final design of the fish passage. Results of the GPR study are provided in Appendix C. The study identified that a buried wood railroad trestle exists within the west portion of the BNSF rail line embankment. January (01/0202) 1-7

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19 Feasibility Study for Restoration of Titlow Lagoon Fish Passage South Puget Sound Salmon Enhancement Group 2. MASTER PLANNING AND SELECTED CONCEPTS FOR TITLOW PARK Metro Parks Tacoma completed a Master Planning process for the overall redevelopment of Titlow Park during the period from August to October Based on this work, the preferred alternative for park redevelopment includes restoration of the lagoon shoreline and installing a rail bridge to restore fish passage to the lagoon. Recommended actions to restore the lagoon include deepening the lagoon, improving the connection between the upper and lower lagoons, and increasing the length and diversity of the lagoon shoreline. These improvements are described further in Section 3. The preferred alternative to restore the lagoon fish passage is to install a bridge in the rail embankment and create a natural tidal channel under the bridge, along with a walkway for pedestrian access to the beach. Installation of a larger culvert pipe under the rail lines was identified as a feasible but less desirable option. Improvements to the existing outlet pipe were also evaluated as a low cost action that might provide immediate benefits. This Feasibility Study examines each of the above options in detail, including presentation of a concept design, identification of construction methods, and estimate of construction costs (see Section 4). Also evaluated was the potential for the new fish passage to increase flooding within the lagoon (see Section 5). Installation of a fish passage structure through the existing, but currently buried, historic pedestrian tunnel under the rail lines located just to the south of the lagoon was considered. This option was concluded infeasible due to 1) the base of the tunnel is at approximately elevation +9 feet MLLW which is too high in the tidal range to be useful as a fish passage; 2) uncertainty about the existing condition of the tunnel structure; and 3) doubt that the floor of the existing tunnel could feasibly be cut out and rebuilt at a substantially lower elevation without substantial risk of damaging the rail lines. January (01/0202) 2-1

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