US Army Corps of Engineers

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2012 Alabama Water Resources Conference Orange Beach, AlabamaSeptember 6, 2012

Beneficial Use Opportunities of Dredged Material from the Upper Mobile Bay Federal Navigation Channel

Larry ParsonPhysical ScientistU.S. Army Corps of EngineersMobile District

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•Approximately 4 MCY of material removed from Mobile Bay Channel annually at a cost of $12 million

•Currently restricted to hopper dredges and transported up to 40 miles for disposal in the Mobile-North ODMDS

•Historically dredging utilized cutterhead dredges with open-water disposal sites along channel

•Hopper dredges not able to keep up with maintenance requirements

•Limits the Corps’ access to smaller % of available dredging fleet

•Removes sediment from system•Exploring beneficial use opportunities

Description & Challenges

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Hopper Dredge

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Hopper Dredge

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Cutterhead Dredge

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• Investigate opportunities to resume in-bay disposal practice options for Mobile Bay navigation channel

•Utilizing environmentally accepted alternatives for beneficial uses of dredged material

•Demonstrate open water disposal with monitoring and predicting movement of sediment associated with in-bay disposal areas

•Utilization of cutterhead dredges providing flexibilities to employ a greater percentage of the available dredging fleet

Goals and Objectives

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Mobile BayInteragency Working Group (IWG)

• Establish and engage IWG to help identify and implement in-bay disposal and beneficial use opportunities

- Alabama Department of Conservation and Natural - State Lands Division ADCNR, Marine Resources Division- Alabama Department of Environmental Management- Alabama State Port Authority- U.S. Fish and Wildlife Service- NOAA, National Marine Fisheries Service- Alabama/Mississippi Sea Grant- Mobile Bay National Estuarine Program - The Nature Conservancy (TNC)

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• Is removing all the dredged sediment from the Bay the smart thing to do?

• Open water disposal has been recently conducted • 1998 – Hurricane Georges• 2005 – Hurricane Katrina

• Mobile Bay is a well studied system with numerous investigations regarding the affects of thin layer disposal showing minimal impacts

• Opportunity to resolve these issues in a manner that is sustainable while maximizing future benefits and minimizing impacts

• What is the best path forward? 

In-bay Beneficial Use Considerations

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• Brookley Hole- Short term- In progress

• In-bay disposal- Long term- In progress

• Tidal marsh creation in upper Bay- Long term- Planning phase

 

Three Beneficial Use Opportunities

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• Old borrow source for creation of Brookley Air Field

• Baseline surveys reveal hypoxic conditions resulting in degraded ecological productivity

• 1.2 MCY of initial fill from upper Mobile Bay Channel

• Fill Options- Fill to some level of productivity- Fill to surrounding grade through

successive dredging cycles- Combination of emergent feature w/

marsh vegetation grading into shallow submerged environment

• Leveraging other research programs- Conducted baseline characterizations- Continued post-fill monitoring

• Monitoring results will be used to determine desired level of restoration

BU of Dredged Material to Fill Borrow Pit (Brookley Hole) – In progress

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Open Bay Disposal in Upper Mobile Bay (In progress)

Northern limit of pipeline dredging

Southern limit of pipeline dredging

Old Hollingers Island Channel

•Hopper dredges not able to keep up with shoaling rates in upper Bay channel

•Critical need to return channel to full operational dimensions

•Utilize hydraulic cutterhead dredges

- 9 MCY dredged from channel

•Thin-layer disposal techniques

•Using pre-established historical disposal areas

•Partnering with other programs to conduct monitoring and modeling

•Significant savings in dredging costs

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Potential Long Term Beneficial Use Sites in Upper Mobile Bay

12

High Priority

1,200 Acres

Medium Priority

780 Acres

Low Priority

700 Acres

BU sites as refined and prioritized from the April 12 Meeting

Establishment of Long Term BU Site in Upper Mobile Bay

• Engagement of Interagency Working Group to help plan and implement semi-contained, large scale open water disposal area in upper Mobile Bay

• BU opportunities associated with navigation activities in Mobile Bay

• Builds on requests of Alabama State Port Authority (ASPA) to partner in implementation of more effective sediment management associated with maintaining Mobile Harbor

• Leverage various funding sources

• Develop feasibility level BU design

• ASPA will take lead on the final design, NEPA coordination, and permitting actions.

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• Establishment of IWG• Emphasize connection between maintenance dredging requirements, beneficial uses, and sediment management methods that reduce dredging costs

• Integration of the regulatory, planning, engineering, and operational processes

• Reducing amount of sediment disposal in the ODMDS• Return sediment into natural system• Establish long-term beneficial use site in upper Mobile Bay• Implementation of environmental restoration alternatives

Benefits to Navigation Program and Environment