RESTORATION OF THE NORTHERN TIP OF MON LOUIS ISLAND Mobile Bay National Estuary Program Fowl River WMP Steering Committee May 19, 2015
Project Site / Background
Historical Maps (Note New Outlet ) 1889 Reference Map 1852 US Coast Survey
Source: Byrnes, M. R., Berlinghoff, J. L., & Griffee, S. F. (2013). Sediment Dynamics in Mobile Bay, Alabama: Development of an Operational Sediment Budget, Final Report.
Project Goals
Project Goals Stabilize the shoreline along the bay side of the northern tip of Mon Louis Island. Create/enhance aquatic, wetland, and upland habitats to the extent possible.
Investigations
Hydrographic and Topographic Survey
Geotechnical Investigations
Coastal Processes Evaluation
Alternatives Evaluation June 2014
Alternate Alignments for Shoreline Stabilization
Shoreline Stabilization Methods Alternative Breakwater / Living Shoreline Concepts Evaluated: Alternative 1 Alternative 2 Alternative 3 Continuous Rock Dike Breakwater Segmented Rock Dike Breakwaters Continuous OysterBreak TM Breakwater Selected Alternative - Continuous Rock Dike Breakwater
Justification for Alternative 1 - Continuous Rock Dike Breakwater: Tried and true measure for stabilizing shorelines in areas of high wave energy. Demonstrated longevity and durability. Aesthetics and public acceptance.
Sources of Fill for Marsh Creation Fowl River navigation channel sediments unsuitable Hauling by truck direct to site infeasible Transport and delivery to site by barge (mechanically unloaded) Beneficial use dredge material sites Commercial borrow sites Costs were estimated at ~$30 to $45 per cubic yard, and such fill sources were ruled out Sandier materials identified in surficial sediments at vibracore locations (SVB-7, 8, 9, and 10), and use of this area as a hydraulic dredging borrow source recommended.
Preliminary Design 50% Design Submittal August 2014
50% Design Features Fill Quantity (in place) Dredge Quantity Total Shoreline Stabilization Length Fill Area (Marsh Creation) 24,800 cubic yards 37,200 cubic yards 1,420 feet 4 acres
Permitting Considerations Pre-application meetings September-October 2014: Viability of proposed open water borrow site questioned. Additional evaluation of dredged material beneficial use sites as potential borrow sites requested. Evaluation of alternate transport and delivery methods suggested. Supplemental Evaluation of Alternatives Report issued February 2015.
Beneficial Use Dredge Material Areas Investigated
Comparison of Estimated Construction Costs Comparative Construction Cost Estimates With Contingencies Engineer s OPC Byrnewood Drive Staging Area (February 2015) $2,281,000 Engineer s OPC Open Water Borrow Alternate (August 2014) $1,654,000 Difference $ 627,000 Comparative Marsh Creation Construction Cost Estimates (Without Contingencies): Engineer s OPC February 2015 $ 1,092,100 Engineer s OPC August 2014 $ 552,000 Difference $ 540,100 For 4 acres of marsh creation: Engineer s OPC February 2015 Engineer s OPC August 2014 Difference $ 273,000 per acre $ 138,000 per acre $ 135,000 per acre
Combine MLI Restoration with Channel Maintenance Funding? Evaluation of Sediments from Fowl River Open Water Disposal Area (April 2015)
Combine MLI Restoration with Channel Maintenance Funding? Advantages: Mobilize one dredge for marsh creation fill and for channel maintenance dredging (cost savings) Environmental clearances already exist for Fowl River open water disposal area Potential impacts of open water borrow area hole (water quality, wave climate) avoided by replenishment with channel sediments
Supplemental Funding for Channel Dredging Requested April 2015; Approved May 2015 ($800,000)
Next Steps Regulatory Coordination and Permits Finalize Engineering Design Bidding and Procurement Construction Monitoring Timeline / Schedule
More Information? Thompson Engineering Emery Baya (251) 665-5431 ebaya@thompsonengineering.com