PWA Dec8

Elkhorn SloughTidal Wetlands Project: 

Elkhorn Slough Tidal Wetlands Project December 8, 2006

Agenda: 

Agenda Scope of work Task integration Framework for projecting geomorphic change

Slide3: 

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

Literature Review – California & Beyond: 

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

Develop / Refine Restoration Concepts: 

Use the existing planning process Refine alternatives proposed in RFP Develop / Refine Restoration Concepts

Previously Identified Concepts: 

Previously Identified Concepts No action Restore historic tidal inlet Reduce opening under Hwy1 Reduce Parsons Slough tidal prism

Integrated Technical Analyses(Tasks C, D, E, & F): 

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

Quantitative Analyses Guided by Conceptual Models: 

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

Natural Morphology of Elkhorn Slough: 

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

Inlet Modifications at Elkhorn Slough: 

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

Prediction of Future Morphology: 

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)

Prediction of Future Morphology: 

Prediction of Future Morphology Source: Elkhorn Slough Foundation Use information generated by the Reserve and others

Physical Changes Affect Habitat(Integration with Task E): 

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 Changing tidal & salinity regimes affect vegetation Inlet closure affects exchange of nutrients, energy, … Marsh plain elevation relative to tides controls hydroperiod

Predicting Future Habitats(Task F): 

Predicting Future Habitats (Task F)

Develop 10% Designs & Costs(Task G): 

Develop 10% Designs & Costs (Task G)

Slide16: 

END

Slide17: 

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 Increased tidal flooding (inundation) Increased tidal volume, range, & velocities 6/26/06 Elkhorn Slough Tidal Wetland Plan Undiked Tidal Marsh Areas - Likely Major Mechanisms of Tidal Habitat Loss and Changes Decreased root biomass Decreased marsh elevations Increased macroalgae abundance Smothers plants Reduced light availability Tectonic events Decreased (mineral) sediment & freshwater supply Decreased (organic) sediment production Elevated nutrient levels (agricultural & urban dev.) Diversion of the Salinas River (agricultural dev.) Groundwater overdraft (agricultural & urban dev.) Sea level rise ? ? 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. Loss of tidal marsh (interior) Plants physically removed by sediment erosion on the marsh plain ? ? Creation of Moss Landing Harbor Deeper estuarine mouth ? ? ? ?

Extension of Applied Geomorphic Tools: 

Extension of Applied Geomorphic Tools

Wave Analysis for Inlet Sizing / Stability: 

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

Application at Bolinas Lagoon: 

Application at Bolinas Lagoon