Download PWA_Dec8 - Elkhorn Slough

Elkhorn Slough
Tidal Wetlands
Project
December 8, 2006
Agenda
• Scope of work
• Task integration
• Framework for projecting geomorphic
change
Tidal
Hydraulics
Study (1992)
Azevedo & BlohmPorter 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
Brown Marsh,
SE Louisiana
Essex marsh,
SE coast of England
Develop / Refine Restoration Concepts
• Use the existing planning process
• Refine alternatives proposed in RFP
Modeling
Team
Agency
Panel
Strategic Planning
Team
Science Panel
Peer Review
Community
Panel
Working
Group
Working
Group
Previously Identified Concepts
2
4
3
1. No action
2. Restore historic tidal inlet
3. Reduce opening under Hwy1
4. Reduce Parsons Slough tidal prism
Integrated Technical Analyses
(Tasks C, D, E, & F)
Task C
Task D
Task E
Assess Inlet
Stability
Hydrodynamic
Modeling
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
Source: Elkhorn Slough Foundation
1854 USC&GS Survey
Historical maps, photographs and surveys
characterize the natural system
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
Use information
generated by the
Reserve and others
Source: CSUMB Seafloor Mapping Lab
Source: Elkhorn Slough Foundation
Physical Changes Affect Habitat
(Integration with Task E)
Task C
Task D
Task E
Assess Inlet
Stability
Hydrodynamic
Modeling
Predict Future
Morphology
6
5
7
Task F
Predict Future
Habitat
5
Inlet closure affects exchange of nutrients, energy, …
6
Changing tidal & salinity regimes affect vegetation
7
Marsh plain elevation relative to tides controls hydroperiod
Predicting Future Habitats
(Task F)
Develop 10%
Designs & Costs
(Task G)
END
6/26/06
Elkhorn Slough Tidal Wetland Plan
Undiked 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.)
Sea level rise
Tectonic events
?
?
?
Decreased marsh elevations
Increased tidal volume,
range, & velocities
Increased tidal flooding
(inundation)
?
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
Decreased
(organic)
sediment
production
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.
Increased macroalgae abundance
• Smothers plants
• Reduced light availability
?
?
?
Decreased
root biomass
?
?
?
Decreased
(mineral)
sediment
& freshwater
supply
Elevated
nutrient levels
(agricultural &
urban dev.)
Diversion of the
Salinas River
(agricultural dev.)
Extension of Applied Geomorphic Tools
Deep Water Wave Power (10^9 ft-lb/ft/yr)
1000
Usuall_closed_M
Closed Inlets
Usuaily_closed_D
Seasonally_closed_M
Seasonally_closed_D
100
Never_closed_M
Never_closed_D
Occasionally_closed_M
Occasionally_closed_D
10
Open Inlets
1
1
10
100
1000
Potential Tidal Prism (Million Cubic Feet)
10000
Wave Analysis for Inlet Sizing / Stability
Transfer
Coefficients
wave period
wave direction
Monterey
Bay Wave
Data
wave period
wave direction
wave direction
wave period
Inlet Wave
Exposure
• Nearshore wave conditions estimated from
offshore data and transformation coefficients
• Use nearshore power for inlet stability analysis
Application at Bolinas Lagoon