DEER LAGOON ALTERNATIVE ANALYSIS

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1 DEER LAGOON ALTERNATIVE ANALYSIS Bob Barnard, WDFW The Deer Lagoon restoration alternatives are divided between those that allow tidal elevations in the western lobe to fluctuate naturally as they do in Useless Bay, and those that create a muted tidal regime. The first three alternatives investigated in the Anchor QEA FEASIBILITY EVALUATION 1 create full tidal inundation in the west lobe and are of the first type. The 4 th alternative is an automatic tide gate which replaces the existing flap gates and limits tidal elevations in the western lobe to levels that do not cause flooding of adjacent properties. The first part of this assessment concerns the tide gate alternative. TIDE GATES All tide and flood gates are considered barriers to fish passage. Attempts have been made to design fish friendly gates, although all gates that control water flow limit the unimpeded active or passive movement of fish, and other organisms that fish depend upon for feeding. In addition, the tide gate, and its attendant dike or road fill, constrains the natural processes that create and sustain the habitat on which fish depend. By their very nature, these gates cause impacts that are probably impossible to mitigate for in their design. If one can accept these impacts to fish passage, habitat and habitat forming functions, then modern gates can provide some lost functions. Historically, tide and flood gates were constructed of cast iron or wood. Plastic, fiberglass and aluminum gates are also available and are preferred because the lighter gates open easier for better fish passage and for drainage. Today s designs include float-operated gates, such as self regulating tide gates (SRT ), automatic electric- or hydraulically-powered gates, and other mechanical systems that allow a specific and variable operating range of upstream water surface elevation. This class is collectively called automatic gates as opposed to passive gates that simply rely on the direction of flow to either close or open. 1 RESTORATION ALTERNATIVES FEASIBILITY EVALUATION: DEER LAGOON RESTORATION, prepared for Wild Fish Conservancy by Anchor QEA, October 2010

2 Figure 1: Longitudinal profile o f a typical tide gate installation showing the major impediments to upstream fish passage. Figure 1 is a longitudinal profile of a typical tide gate and culvert installation showing the major impediments to fish passage. A fish or other organism experiences the tide gate from the salt to the freshwater side. Regardless of the type, the elevation of the tide gate in the water column influences fish passage. At lower tidal elevations, adult upstream migrants move up the channel and if they encounter a culvert elevated above the channel bed, perched, they are prevented from moving into the culvert. Juvenile fish move in the nearshore in the top part of the water column. If the tide gate and culvert are small compared to the tidal range, then fish are not likely to find it as the move along the shore during higher tide elevations, being predisposed to remain in the upper few feet of water. The tide gate s material and operating mechanism influence it s passability, but it is never considered 100% passable. The velocity and depth in the barrel of the culvert may exceed the swimming ability of the fish the make it past the gate. There is often an increase in velocity at the inlet of the culvert as flow contracts into the smaller culvert. Head loss in excess of 0.5 feet (velocity greater than 5 feet per second) is likely to be a barrier to juvenile and weak swimming fish. For automatic tide gates, and open tidally influenced culverts, the barrel velocity and head loss is a function of not only the freshwater design flow (10% exccedance flow for migration period), but also the discharge associated with the ebb of the tidal prism stored above the tide gate. NOAA Fisheries Science Center and the Skagit River Systems Cooperative are engaged in an ongoing study of the effects of fish friendly tide gates on fish abundance and migration. They have preliminary results that indicate that automatic-type tide gates on tidal sloughs, which remain open for part of the flood tide, negatively affect the abundance and movement of juvenile Chinook salmon when compared to similar but un-gated sloughs. Some specific preliminary findings: Juvenile Chinook are present in lower numbers upstream of automatic tide gated sloughs than where found in un-gated sloughs These fish tended to spend less time behind the tide gate 2

3 Tagged fish were shown to move less frequently across the gate and, in the case of larger fish released above the gate, to move only once downstream and out of the slough. Indications are that the muted tidal cycle created by the automatic tide gate results in reduced habitat quality which may be reflected in lower abundance with fewer repeated visits by juvenile Chinook. Tide gates alter the salinity, temperature, DO, TSS, etc of the habitat upstream so it is a matter or quality of habitat as well as access to it. These preliminary results suggest that tide gates designed to better accommodate fish passage may have only limited benefits for fish populations. More results should be available in the next few years. The importance of these preliminary findings is that the impacts of dikes and tide gates cannot be completely compensated for by automatic tide gates. The ecological impact of tide gates in estuaries goes beyond being fish-migration barriers. C. A. Simenstad and R. M. Thom 2 found that a number of environmental factors are affected by tide gates. They modify hydrology, vegetation and the general ecosystem functioning of coastal wetlands. Among these factors are surface-water and groundwater elevation, sedimentation, salinity, soil texture and creek morphology. Their influence on water quality may be substantial. A saline marsh can be converted to a freshwater marsh when it is located upstream of a tide gate. When saltwater estuarine habitats are lost or degraded, so are the important and unique functions they provide, such as shoreline stability, water quality, trophic energy (food web) support, fish and wildlife habitat for different species, recreation, promotion of biodiversity, and the maintenance of microclimate characteristics. The importance of hydrological connection has been repeatedly emphasized by other researchers 3,4,5. These environmental impacts drastically alter the basic 2 Simenstad, C. A. and R. M. Thom Restoring Wetland Habitats in Urbanized Pacific Northwest Estuaries. Pp In G. W. Thayer, editor, Restoring the Nation s Marine Environment. Maryland Sea Grant, College Park, MD. 3 Zedler, J. B Salt Marsh restoration: A guidebook for southern California. La Jolla, CA. Department of Biology, San Diego State University (California Sea Grant Project Report No. T-CSGCP-009). 4 Kusler, J. A. and M. E. Kentula Wetland creation and restoration: the status of the science. Corvallis, OR. U.S. Environmental Protection Agency, Environmental Research Laboratory 5 Fresh, K., C. Simenstad, J. Brennan, M. Dethier, G. Gelfenbaum, F. Goetz, M. Logsdon, D. Myers, T. Mumford, J. Newton, H. Shipman, C. Tanner Guidance for protection and restoration of the nearshore ecosystems of Puget Sound. Puget Sound Nearshore Partnership Report No Published by Washington Sea Grant Program, University of Washington, Seattle, Washington. Available at 3

4 chemistry, tidal characteristics and ecology of the upstream area. Such changes likely work cumulatively and in concert with the migration-barrier impact to further affect fish production. RESTORATION ALTERNATIVES Considering the risk and known impacts of tide gates, of whatever type, the only alternatives that lead to meaningful nearshore restoration at Deer Lagoon are levee breaching and levee removal. The following alternatives were proposed in the FEASIBILITY EVALUATION (Anchor QEA, 2010) and shown in Figure 2. Figure 2: Deer Lagoon alternatives. Alternative 1: single breach of levee; a single 100 foot wide breach at the current tide gate location. Alternative 2: double breach of levee; in addition to the Alt 1 breach, a second 100 breach is added midway down the existing levees. Alternative 3: complete levee removal. 4

5 Alternative 4: replacing the existing tide gate with an automatic tide gate (covered in the first section of this report). Alternatives 2-4 require a setback levee to protect the Shore Road community from high tides. The FEASIBILITY EVALUATION recommends that the elevation of the setback levee be the maximum water surface elevation due to tide (11.4 ft, MLLW datum) plus an additional amount for wind and wave set up (3.1 ft) for a final elevation of 14.5 ft. To this is added an amount for settlement and a factor of safety which depends on an evaluation of risk. Settlement can only be determined after analyzing the underlying soils, which is part of the geotechnical assessment (see GEOTECHNICAL ASSESSMENT SCOPE OF WORK, Page 11). The risks associated with the setback levee are difficult to assess; Useless Bay water will flow over Shore Road (elevation about 14 ft) before it will overtop the setback dike since wind-driven waves will be higher on the bayfront than they will be back in the lagoon. Water will then be trapped between the levee and Shore Road and a tide gate system should be set into the levee to drain this water off at low tide. The location of this setback dike is balance between maximizing restoration area, minimizing impacts to the community, and providing storage area for wave overwash during storm events and high tide. Restoration activities can only take place when land owners are cooperative. It is important to determine community expectations concerning flooding and other damage related to storms and how this could affect setback dike design. Figure 3 shows the relative relationships between these elements. More detailed drawings of the setback dike can be found in Appendix B. Figure 3: North-south cross section through the shoreline community, setback levee, and Deer Lagoon (not to scale) In Puget Sound, restorations have favored levee removal over breaching for a number of reasons. The most obvious is that intertidal habitat lies under the levee itself and removal makes this area available for restoration. More importantly, simply breaching a levee returns tidal inundation 5

6 without restoring the estuarine system. 6 It has been found that breaching reduces the amount and extent of sediment deposition within the breached dike area. 7 Breaching also reduces the area and complexity of tidal channel development as compared to areas of complete removal 8. Breaches also influence the distribution of suspended materials and organisms 9. Hydraulically, breaching modifies the patterns of circulation and salinity stratification. All of these things influence the performance of the restoration in deleterious ways. One way to approach levee removal alternatives is to evaluate the hierarchy of benefits and costs associated with each (this method was initially developed by Phillip Williams and Associates for the PSNERP Conceptual Engineering Design Report 10 ). In order to illustrate how much ecological benefits increase as opening size increases, assessments we carried out on several general categories of crossings. These crossing types are evaluated within the 4 constraints to processes in a qualitative and quantitative way in Table 1 (appears on pages 9 and 10) and discussed below. These quantities represent the proportional decrease in a given stressor or constraint. The numbers in Table 1 have been adjusted to suit these conditions. Overall, our understanding of the situation is that constraints to hydraulic and water quality processes are relatively easy to remove; that sedimentary ones more difficult; and geomorphic process are the most difficult to restore. The goal of this analysis is to use the relative sum of benefits, shown in the last row, combined with the relative costs to evaluate each alternative. The alternative which meets the project goals and does so with the lowest incremental cost, is preferred. Table 2 shows each alternative and the associated costs and benefits. The costs are measured by the length of dike removed from between the central and western lobes, and built as flood protection for the residential community along Shore Road. These costs are based on simplified assumptions and contain a high level of uncertainly (see Appendix A: cost estimates). The 6 Pethick, J. (2002). "Estuarine and tidal wetland restoration in the United Kingdom: Policy versus practice." Restoration Ecology 10: ENSR and D. Unlimited (1999). Nisqually National Wildlife Refuge - Habitat Management and Restoration Project: Hydrodynamic and Sediment Transport Model: ENSR Document (2). 8 Hood, G. (2004). "Indirect environmental effects of dikes on estuarine tidal channels." Estuarine Research Foundation 27(2): French, J. R. and D. R. Stoddart (1992). "Hydrodynamics of salt marsh creek systems: Implications for marsh morphological development and material exchange." Earth Surf. Processes Landforms 17: ESA /PWA Puget Sound Nearshore Ecosystem Restoration Project: Strategic Restoration Conceptual Engineering - Final Design Report: Appendix C. 6

7 Setbak dike length Dike length removed Estimated costs ($millions) Relative sum of benefits Benefit costs Uncertainty Uncertainty costs Deer Lagoon Alternatives Analysis Alternative 1 automatic tide gate cost is based on the hydraulic automated tide gates installed at the Julia Butler National Wildlife Refuge near Cathlamet, WA in The relative sum of benefits is taken from the final row in Table 1. Benefits costs are the estimated costs divided by the relative sum of benefits to give a dollars per benefit measure: alternatives with relatively few benefits result in a higher cost-per-benefit than those with many benefits. The uncertainly column represents the likelihood that the project will not deliver the restoration benefits as intended in the design. In the restoration world, restoration projects based on highly engineered solutions, rather than natural processes, are less likely to fail to perform as expected. Using natural processes promotes ecosystem resilience 11 and ecological succession 12 which ensure continued benefit despite changes in inside and outside factors. In order to use uncertainty to help differentiate alternatives, it is interpreted as a cost in the final column (uncertainty x benefit costs). Table 2: Cost-benefits of the 4 alternatives for the Deer Lagoon restoration. Alt % Alt % Alt % Alt % Greiner, Courtney M Principles for Strategic Conservation and Restoration. Puget Sound Nearshore Ecosystem Restoration Program, Technical Report , Olympia, WA. 12 Goetz, F., C. Tanner, et al Guiding Restoration Principles, Technical Report , Puget Sound Nearshore Partnership (PSNP). 7

8 The costs and uncertainty are shown in graphical form in Figure 4. It is clear from this chart that alternative 3 has the lowest benefit and uncertainly costs, based on the assumptions behind the values in Tables 1 and 2. While the analysis is based on numbers, they are mostly a subjective assessment of the probability of success, not measurements of physical quantities. As part of the continuing design process a more exhaustive analysis may be desired Uncertainty costs Benefit costs Alt 4 Alt 1 Alt 2 Alt 3 Figure 4: Chart showing the benefit costs (estimated costs/relative sum of benefits) and the uncertainty costs (uncertainty x benefit costs) for the 4 Deer Lagoon alternatives. Vertical axis scale is in dollars per relative habitat benefit units. 8

9 Tide gate Automatic tide gate Single breach Double Breach Complete removal Deer Lagoon Alternatives Analysis Alternative Process Structural Impact Functional Response Hydraulic/ Hydrodynamic Process Impacts Sedimentary process impacts Alteration of tidal stage characteristics Alteration of salinity distribution Elimination of storm surge overwash across beach Alluvial sedimentation altered by backwater affects Estuarine sedimentation limited by reduction in tidal flows Lowering of high tide elevations - isolates marsh plains and causes conversion to fresher habitats Raising low tide elevations reduces area area of intertidal mudflat/sandflat habitat Raising mean tide elevations affecting marsh-to-forest transition Reduction in tidal frame Reduction in tidal prism in marsh Reduced tidal excursion Vertical salinity stratification degraded through mixing Salinity mixing zone length truncated- squeezing and reduction of brackish zone habitats Transport of large woody debris into marsh Mobilization of detritus due to storm surge wave action eliminated Fine sediment accumulates on marsh plain, shift to upland habitats Coarse sediment accumulates in tidal channels Reduced tidal prism reduces sediment delivery to marsh plain, causes lowering relative to tidal frame Increased turbidity in tidal channels due to Reduce marsh productivity and loss of aquatic habitat area Reduction of benthic productivity and low interitdal habitat Change in productivity, species composition and organic export Water table fluctuation limited, affecting plant growth Channel system atrophies through sedimentation; reduced channel connectivity Passive advective transport of organisms in and out of estuary diminished Reduction of passive transport of organisms into estuary through baroclinic circulation Salinity changes, reduced qualityof rearing habitat Habitat heterogeneity reduced Export of nutrients to estuary reduced Category total Reduce marsh productivity Loss of blind channel habitat Reduced productivity of marsh vegetation Adverse affect on benthic organisms and eelgrass na na na na na

10 Geomorphic Impacts Water Quality Impacts Alteration of entrance channel morphology from broad shallow to narrow Atrophied tidal drainage system Marsh plain elevations changed Increased residence time Accumulation of toxics loss of marsh plain sediment sink Increased tidal velocity through entrance creates scour holes Channel location fixed instead of lateral migration affecting ebb and flood shoal extent Fixed channel location may lead to permanent closure of confined marsh by longshore drift Tidal channels shallower Dendritic tidal channel system becomes disconnected Lowered marsh plain Areas raised by alluvial sedimentation Reduction in tidal exchange Reduction in tidal excursion Reduced tidal scouring allows accumulation of polluted sediments from watershed Reduced residence time means concentration of dissolved pollutants in water column is higher Category total countermeasures reduce habitat value Reduced production of benthic organisms Eliminates exchange of water, sediment, nutrients and organisms Degraded estuarine habitat Degraded estuarine habitat Reduced marsh productivity Change to freshwater or upland species Category total Algal blooms in marsh channels, anoxic in poorly drained holes Export of water column productivity to larger estuary limited Toxic affects on organisms Toxic affects on organisms Category total Sum of ecological benefits Relative sum of benefits 0% 14% 47% 64% 100% Table 1: calculation of benefits of 4 alternatives for Deer Lagoon based on a conceptual model of estuary restoration. 10

11 GEOTECHNICAL ASSESSMENT SCOPE OF WORK Wild Fish Conservancy is seeking to execute a contract to perform a geotechnical assessment of potential habitat restoration actions at Deer Lagoon on Useless Bay, Washington. This contract may be extended to include engineering design and specifications for the construction of this work. Deer Lagoon has been modified by levee construction and tide gates for agricultural and infrastructure purposes reducing the value of fish habitat and interfering with the natural processes that normally create and maintain such habitat. The proposal is to investigate the removal of some portion of the existing levees and the construction of a setback levee. The scope is expected to include these tasks: 1. Research background information including geologic records, historical maps and aerial photographs, and design drawings for the Shore Road residential community. 2. Perform a field reconnaissance of the existing dike system for overtopping, seepage, settlement, and slope instability that could affect setback dike design. At the same time, perform a field reconnaissance of the Shore Road Community for evidence of storm overwash and storage north of the community. 3. Perform subsurface explorations in the proposed setback dike locations. Exact number and locations to be determined on site, but not to exceed 8. Samples of the existing levee material should also be taken to determine the possible reuse or possible disposal options. 4. Perform soil index and strength testing on select soil samples to characterize soil geotechnical and hydrogeologic properties, including strength, compressibility, and hydraulic conductivity. 5. Perform preliminary stability and settlement analyses to develop concept-level dike design recommendations. Identify major risks that may be associated with any of the potential alternatives. 6. Investigate feasibility of alternative methods of delivering potable water to the Shore Road Community (such as boring with trenchless technology below the current alignment, or relocating along South Double Bluff Road). Previous work on this project includes: Restoration Alternatives Feasibility Evaluation: Deer Lagoon Restoration, prepared for Wild Fish Conservancy by Anchor QEA, October Deer Lagoon Alternative Analysis, Bob Barnard, WDFW, April 29,

12 APPENDIX: SETBACK DIKE The setback dike construction is based on Lidar data supplied by Anchor QEA, Inc. Figure 5 shows the setback dike alignment and the location of 5 cross sections. Figure 5: Deer Lagoon DEM showing location of setback dike and 5 cross sections. Figure 6 shows a typical dike cross section. The details of this structure must be resolved at later stages of design when site survey and geotechnical investigations are completed. Side slope is assumed to be 2.5h:1v but must be based on dike materials and other design criteria. The top 12

13 width is 10 ft, which is drivable but does not meet typical flood protection standards. The height of the dike is based on the elevation of the surrounding ground and a top elevation of 14.5 ft. Based on soils investigation and inundation frequency, there may need to be a cutoff trench beneath the dike. The elevation of MHHW is 10.4 ft, which is just slightly above the mean elevation of the ground on the setback dike alignment. This means that the dike will be wetted less than 10% of the time and mostly less than about 1 ft up its flank. There will be times that 3.5 ft of depth will be on the northern side, but this will be infrequent and of short duration. Value engineering in the design phase of this dike could create substantial savings Avg. Ht. 4.5 Elevation 14.5 MLLW Figure 6: Typical setback dike dimensions (NTS). Typical cross sectional area is 3.5 cubic yards. Figure 7 shows the 5 cross sections indicated in Figure 5. The seback of the dike from Shore Rd is somewhat arbitrary and a more systematic evaluation may improve its performance and lower the cost. It generally crosses emergent wetlands, an impact that will have to be mitigated, although the conversion of the current freshwater wetland to a high value tidal salt marsh will, in part, compensate. 13

14 Figure 7: Deer Lagoon setaback dike cross sections (NTS) Xsec

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