Expected Long Term Site Evolution of Alameda Creek and former Salt Ponds following Tidal
Marsh Restoration
Matt [email protected]
Philip Williams & Associates
Presentation Summary
Development of future channel and marsh plain conditions to better inform flood modeling of Alameda Creek and Old
Alameda Creek using geomorphic design tools from similar tidal marsh restoration sites
- Project overview
- Development of long term site conditions
- Hydrodynamic modeling application
Overview – Setting
Downstream reach of the creekfrom Ardenwood Blvd to the Bay
Major flood control facility designedby USACE
Conveyance capacity reduced by sedimentation
Overview – Project Goals
Work with Alameda County to develop conceptual alternatives for the Eden Landing area that:
1 - Maintain or increase flood protection on Alameda Creek Flood Control Channel and Old Alameda Creek
2 - Integrate with South Bay Salt Ponds restoration alternatives
3 - Examine long term conditions ( ~50 years )
• Channel evolution
• Marsh plain sedimentation
• Sea Level Rise
Overview – SBSP Project Description
Each SBSP programmatic alternative integrates:
- habitat restoration
- flood management
- public access
Overview – SBSP Alternatives
The SBSP programmatic alternatives are:
• Alternative A: No Project Alternative
• Alternative B: Mix of Tidal Habitat (50%) and Managed Pond (50%)
• Alternative C: Mix of Tidal Habitat (90%) and Managed Pond (10%)
Alternatives B and C are the
same for the E2 pond complex
Supplemental Alternatives
Short Term (development)
- Breaches (internal and external levees) will maximize channel scour & are based on thehistoric channel network
Long Term (evolution)
- Cross section and breach dimensions were estimated usinghydraulic geometry relationships
- Restored marsh areas were assumed to increase in elevation to MHHW (w/ sea level rise) &develop channels based on historic channel network
Supplemental Alternatives
Short Term (development)
- Breaches (internal and external levees) will maximize channel scour & are based on thehistoric channel network
Long Term (evolution)
- Cross section and breach dimensions were estimated usinghydraulic geometry relationships
- Restored marsh areas were assumed to increase in elevation to MHHW (w/ sea level rise) &develop channels based on historic channel network
Scour
Long-term
Scour enlarges channel
Sedimentation reduces conveyance & storage
• Levees separate channels from adjacent salt ponds
• Channels fill in with sediment and salt ponds subside
• Levee lowering/ removal causes channel scour and marsh sedimentation
• Salt pond restoration can reduce fluvial flood hazards through increased conveyance
Scour
Salt pondFlood control
channel
Existing Condition
Scour
Water level decreases
Immediately After Construction
Floodplain storage and conveyance increase
Tidal Scour and Fluvial Flooding
Tidal Scour
2004
Tidal prism = 26 million ft3
1996
Tidal prism = 1 million ft3
Sonoma Baylands Main Channel
Historic channels were used to locate breaches
Levee Breach Locations
Supplemental Alternative 1
Levee Breach Locations
Supplemental Alternative 2
Levee Breach Locations
Supplemental Alternative 3
Levee Breach Locations
Supplemental Alternatives
Short Term (development)
- Breaches (internal and external levees) will maximize channel scour & are based on thehistoric channel network
Long Term (evolution)
- Cross section and breach dimensions were estimated usinghydraulic geometry relationships
- Restored marsh areas were assumed to increase in elevation to MHHW (w/ sea level rise) &develop channels based on historic channel network
Cross Section Development
What is hydraulic geometry?
A set of empirical geomorphic A set of empirical geomorphic relationships that predict tidal relationships that predict tidal
channel cross section dimensions channel cross section dimensions as a function of contributing marsh as a function of contributing marsh
area or tidal prismarea or tidal prism
- Developed for SF Bay - Marshes from 2 to 5,700 ha
- Design tool for restoration projectsWilliams, Orr, & Garrity (2002)
Breach sizes were based on anticipated drainage areas (estimated from historic network and interior levee layout)
Cross Section Development
-15
-10
-5
0
5
10
15
20
-500 -400 -300 -200 -100 0 100 200 300 400 500 600
Station (ft)
Ele
vatio
n (f
t N
GV
D)
2001 cross section2007 cross sectionAlt 2 - Long Term with Scour cross sectionUSACE Design cross section
Cross Section Development
Cross section example
depth
widthMHHW
Restored Marsh Areas
- Former salt ponds will eventually fill with sediment to the elevation ~MHHW (including sea level rise)- Sediment supply in South Bay is sufficient to fill former ponds
Assumed sea level rise of 0.15 meters
over 50 years
PWA, 2006. South Bay Geomorphic Assessment. Prepared for California State Coastal Conservancy, US Fish & Wildlife Service, California Dept. of Fish and Game.
Restored Marsh Areas
Long term bathymetry includes sedimentation, sea level rise, and estimated channel network (based on historic channels)
Hydrodynamic Modeling
MIKE Flood: 1-D (MIKE 11) and 2-D (MIKE 21) models Connected through lateral and standard links
Ardenwood Blvd
880
Modeling Description
Model runs
- Short term, post breach conditions - no scour, no sedimentation
- Long term, ‘worst case’ conditions- no scour, with sedimentation & sea level rise
- Long term, most likely conditions- with scour, sedimentation, & sea level rise
- Long term, no action conditions- with levee failures - with scour, sedimentation, & sea level rise
Model Results
Reduction in peak water levels at Ardenwood Blvd - Larger channel dimensions - Reduction in flow (routed through salt ponds)
0
5
10
15
20
25
30
35
0 5,000 10,000 15,000 20,000 25,000 30,000Station (ft)
Ele
vatio
n (f
t N
GV
D)
SPF Water Surface Elevation
Alt 2 - Short Term
Alt 2 - Long Term - No Scour
Alt 2 - Long Term - With Scour
Right (North) Levee Crest (as schematized in MIKE Flood)
SF Bay
Ardenwood Blvd
DRAFTDRAFT
Water surface and levee crest elevations
Conclusion
- Long term conditions should be considered in any design - Long term site geometry (channels and marshes) can be predicted from analogous tidal marsh restoration sites
- Tidal marsh restoration can be beneficial to flood management and flood control
Questions?
Thanks to: Alameda County Flood Control and Water Conservation District
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