Expected Long Term Site Evolution of Alameda Creek and former Salt Ponds following Tidal

Marsh Restoration

Matt Wicklandm.wickland@pwa-ltd.com

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