Elkhorn SloughTidal 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)

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

Essex marsh, SE coast of England

Brown Marsh, SE Louisiana

• Use the existing planning process• Refine alternatives proposed in RFP

Strategic Planning Team

Science Panel

Agency Panel

Community Panel

Peer ReviewWorking Group

Working Group

Modeling Team

Develop / Refine Restoration Concepts

Previously Identified Concepts

1. No action

2. Restore historic tidal inlet

3. Reduce opening under Hwy1

4. Reduce Parsons Slough tidal prism

2

4

3

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

• 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

Historical maps, photographs and surveys characterize the natural system

Source: Elkhorn Slough Foundation 1854 USC&GS Survey

Inlet Modifications at Elkhorn Slough

• New ocean inlet• Armored jetties• Maintenance dredging

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

Source: Elkhorn Slough Foundation

Use information generated by the Reserve and others

Source: CSUMB Seafloor Mapping Lab

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

56

7

Changing tidal & salinity regimes affect vegetation6

Inlet closure affects exchange of nutrients, energy, …5

Marsh plain elevation relative to tides controls hydroperiod7

Predicting Future Habitats(Task F)

Develop 10% Designs & Costs

(Task G)

END

Loss of tidal marsh (edges)• Plants physically removed by bank erosionErosion 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

6/26/06Elkhorn 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

1

10

100

1000

1 10 100 1000 10000

Potential Tidal Prism (Million Cubic Feet)

Dee

p W

ater

Wav

e P

ow

er (

10^

9 ft

-lb

/ft/

yr) Usuall_closed_M

Usuaily_closed_D

Seasonally_closed_M

Seasonally_closed_D

Never_closed_M

Never_closed_D

Occasionally_closed_M

Occasionally_closed_D

Open Inlets

Closed Inlets

wave period

wav

e di

rect

ion

wave period

wav

e di

rect

ion

Monterey Bay Wave

Data

wave period

wav

e di

rect

ion

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