elkhorn slough tidal wetlands project december 8, 2006
TRANSCRIPT
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