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Elkhorn Slough Tidal Wetlands Project

Elkhorn Slough Tidal Wetlands Project. December 8, 2006. Agenda. Scope of work Task integration Framework for projecting geomorphic change. Tidal Hydraulics Study (1992). Azevedo & Blohm-Porter Enhancement Plans (1991-1995). Stanford 3D Modeling (ongoing).

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Elkhorn Slough Tidal Wetlands Project

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  1. Elkhorn SloughTidal Wetlands Project December 8, 2006

  2. Agenda • Scope of work • Task integration • Framework for projecting geomorphic change

  3. Tidal Hydraulics Study (1992) Azevedo & Blohm-Porter Enhancement Plans (1991-1995) Stanford 3D Modeling (ongoing) Strategic Planning (2004–2006) ESNERR Initiates the TWP Task A: Literature Review of Management Actions Task B: Develop Restoration Alternatives Task C, D, E, & F Technical Analyses Selection of Preferred Alternatives Task G: Develop Conceptual Designs

  4. Literature Review – California & Beyond Brown Marsh, SE Louisiana Essex marsh, SE coast of England

  5. Peer Review Strategic Planning Team Working Group Working Group Modeling Team Science Panel Agency Panel Community Panel Develop / Refine Restoration Concepts • Use the existing planning process • Refine alternatives proposed in RFP

  6. 2 4 3 Previously Identified Concepts • No action • Restore historic tidal inlet • Reduce opening under Hwy1 • Reduce Parsons Slough tidal prism

  7. Integrated Technical Analyses(Tasks C, D, E, & F) Task C Assess Inlet Stability Task D Hydrodynamic Modeling Task E Predict Future Morphology Task F Predict Future Habitat

  8. Quantitative Analyses Guided by Conceptual Models • Provides an ‘intellectual roadmap’ for understanding & predicting changes • Highlights ‘cause-and-effect’ pathways useful during alternative analysis • Directs inlet analysis, computer-based modeling, and geomorphic projections

  9. Natural Morphology of Elkhorn Slough Source: Elkhorn Slough Foundation 1854 USC&GS Survey Historical maps, photographs and surveys characterize the natural system

  10. Inlet Modifications at Elkhorn Slough • New ocean inlet • Armored jetties • Maintenance dredging

  11. Prediction of Future Morphology Step 1: Understand the Geomorphic System • Identify geomorphic units & sediment budget elements • Analyze how physical processes will change Step 2: Project Change • Predict change of each unit • Assess if sediment budget can accommodate cumulative effects Step 3: Integration with Other Tasks • Predicted morphology is bathymetry of modeling (Task D) • Planform map of units influences habitat (link Task F)

  12. Source: CSUMB Seafloor Mapping Lab Prediction of Future Morphology Use information generated by the Reserve and others Source: Elkhorn Slough Foundation

  13. 5 6 7 6 5 7 Physical Changes Affect Habitat(Integration with Task E) Task C Assess Inlet Stability Task D Hydrodynamic Modeling Task E Predict Future Morphology Task F Predict Future Habitat Inlet closure affects exchange of nutrients, energy, … Changing tidal & salinity regimes affect vegetation Marsh plain elevation relative to tides controls hydroperiod

  14. Predicting Future Habitats(Task F)

  15. Develop 10% Designs & Costs(Task G)

  16. END

  17. 6/26/06 ? ? Elkhorn Slough Tidal Wetland PlanUndiked Tidal Marsh Areas - Likely Major Mechanisms of Tidal Habitat Loss and Changes Creation of Moss Landing Harbor Deeper estuarine mouth Groundwater overdraft (agricultural & urban dev.) Tectonic events Sea level rise ? ? ? Decreased marsh elevations Increased tidal volume, range, & velocities Increased tidal flooding (inundation) ? Decreased (organic) sediment production Decreased (mineral) sediment & freshwater supply • Loss of tidal • marsh (interior) • Plants physically • removed by sediment • erosion on the marsh • plain • Loss of tidal marsh (edges) • Plants physically removed by • bank erosion • Erosion of channel & tidal • creeks • Extended tidal creek network • Erosion of soft sediments • from mudflats & marsh plain • Loss of tidal marsh (interior) • Marsh elevation not keeping pace • with water levels exceeding plants • physiological constraints (drowning) • Plant death likely caused by • anoxic soil conditions • Plants more susceptible to • disease, etc. ? ? Decreased root biomass ? Diversion of the Salinas River (agricultural dev.) Elevated nutrient levels (agricultural & urban dev.) ? • Increased macroalgae abundance • Smothers plants • Reduced light availability

  18. Extension of Applied Geomorphic Tools

  19. Wave Analysis for Inlet Sizing / Stability • Nearshore wave conditions estimated from offshore data and transformation coefficients • Use nearshore power for inlet stability analysis wave period wave period wave period Monterey Bay Wave Data Transfer Coefficients Inlet Wave Exposure wave direction wave direction wave direction

  20. Application at Bolinas Lagoon

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