Mobile Bay National Estuary Program Project Implementation Committee Meeting

Transcription

1 Mobile Bay National Estuary Program Project Implementation Committee Meeting Mobile Bay Interagency Working Group Activities Larry Parson U.S. Army Corps of Engineers, Mobile District February 18, 2016 High Priority 1,200 Acres Trusted Partners Delivering Value, Today and Tomorrow Low Priority 700 Acres Medium Priority 780 Acres US Army Corps of Engineers

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3 Challenge WRDA 1986 Authorization for widening and deepening Dredged material from Mobile Channel shall be disposed of in open water in the Gulf of Mexico WRDA 1996 May consider alternatives to disposal of dredged material in the Gulf of Mexico, including environmental acceptable alternatives for beneficial uses of dredged material and environmental restoration Is removing all the dredged sediment from the Bay the smart thing to do? 3

4 Mobile Bay RSM Watershed Study Recommendations Evaluate alternative management options Development of in-bay disposal strategies both short and long term Considerations for an in-bay disposal demonstration project 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 Establish interagency working group to develop a sediment management strategy

5 Mobile Bay Interagency Working Group (IWG) Alabama State Port Authority (ASPA) USACE, Mobile District USACE, Engineering Research and Development Center (ERDC) Alabama Dept. of Conservation and Natural Resources (ADCNR), State Lands Division ADCNR, Marine Resources Division (MRD) ADCNR, Wildlife and Freshwater Fisheries Division (WAFF) Alabama Dept. of Environmental Management (ADEM) Geological Survey of Alabama (GSA) U.S. Fish and Wildlife Service (FWS) National Marine Fisheries Service (NMFS), Habitat Conservation Division Mobile Bay National Estuary Program (NEP) Environmental Protection Agency (EPA) Dauphin Island Sea Lab (DISL) The Nature Conservancy (TNC) Mobile County Environmental Department Mobile Bay Keeper

6 Interagency Working Group Goals Development of in-bay disposal strategies both short and long term Utilizing environmentally accepted alternatives for beneficial uses of dredged material Identify, evaluate, and utilize new and existing engineering techniques and management models/tools to evaluate alternative management options 6

7 IWG History February 9, 2012 Initial meeting to introduce Corps RSM Program April 19, 2012 Identified potential opportunities June 12, 2012 Initial discussions on TLD emergency action Refine BU site and Brookley Hole November 8, 2012 Needed actions for BU site Discussions on TLD monitoring/modeling March 18, 2014 Present results of TLD monitoring/modeling Brookley Hole monitoring results December 10, 2014 Projects status Upper Bay BU site December 9, 2015 Projects status Brookley Hole Recommendations Mobile Harbor GRR Agency Scoping 7

8 Accomplishments Mobile Bay Sediment Budget - Funded primarily by MBNEP Brookley Hole - Short term - Two placement activities In-bay disposal - Long term - Added as permanent option Tidal marsh creation in upper Mobile Bay - Long term - planning phase - Submitted to RESTORE Council 8

9 Sediment Dynamics in Mobile Bay: Development of an Operational Sediment Budget Applied Coastal Research and Engineering, Inc. Mobile Bay National Estuary Program U.S. Army Corps of Engineers Contributing 9

10 Mobile Bay Sediment Budget Document long-term regional sediment dynamics in Mobile Bay for developing a sediment budget Compile historical channel dredging and placement quantities to document sediment movement due to engineering activities Compile and analyze historical shoreline and bathymetry data for Mobile Bay 10

11 BU of Dredged Material to Fill Brookley Hole Borrow source for creation of Brookley Air Field Surveys revealed that the Hole is ~65 acres in size with a maximum depth of about 22 feet. Baseline surveys revealed hypoxic/anoxic conditions resulting in degraded ecological productivity. There was minimal benthic infauna and very little finfish usage of the bottom half of the water column during the warmer months.

12 BU of Dredged Material to Fill Brookley Hole Recommendation to pursue permitting processes to implement BU action 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 1.2 MCY of initial fill from upper Mobile Bay Channel Monitoring results used to determine desired level of restoration Initial fill completed September 2012 Leveraging other research programs (DOER) - Conducted baseline characterizations - Continued post-fill monitoring

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14 Example Echograms for Summer, Winter and Spring Sampling at Brookley Hole.

15 Normal Discharge TURBID WATER SILT CURTAIN FLOCCUL ATED MATERIA L Cl/RR NT BOTTOM SEDIMENT (Saucier et al. 1978)

16 Baffled Bottom Discharge

17 Typical Pre- & Post-Placement Profiles 02/ / / / / /2011

18 DO (mg/l) concentrations during pre- and post-restoration sampling within Brookley Hole. (Note: Seasonal results are averaged across five stations occupied within the borrow pit.)

19 During the summer sampling, the number of animals per sample increased significantly (p < 0.05) from 2 (pre) to 102 (post-restoration) per sample, resulting in an increase in density from 45 animals/m 2 to 2,315 animals/m 2, a percentage change of +5,044%.

20 BU of Dredged Material to Brookley Hole Brookley Hole Monitoring Results - No evidence of post-restoration hypoxia/anoxia - Fish density increased during spring and fall - Significant increase in benthic diversity and abundance but still recovering IWG recommended continued placement - Summer 2014 dredging cycle - Additional 750,000 cy placed - Hydrographic surveys and DO monitoring after consolidation - Further recommendations using results of monitoring

21 2014 Placement Beneficial use objective has been achieved Further placement above grade requires containment and other technical constraints IWG recommends no further placement at this time Future placement may be warranted if significant consolidation occurs Area that s been ecological unproductive restored to approximately 50 acres of productive bay bottom Provided significant savings to the O&M maintenance costs for Mobile Harbor

22 Open Bay Disposal in Mobile Bay Northern limit of pipeline dredging Approximately 4 mcy of material removed from Mobile Bay Channel annually at a cost of $12 million Old Hollingers Island Channel Southern limit of pipeline dredging Hopper dredges not able to keep up with shoaling rates in upper Bay channel Critical need to return channel to full operational dimensions Channel width compromised

23 Thin-layer Disposal Considerations WRDA Requirements Is removing all dredged sediment from the Bay the smart thing to do? Current dredging practices not able to keep up Open water disposal has been recently conducted 1998 Hurricane Georges 2005 Hurricane Katrina 2012 recertification included emergency open-bay option IWG Concerns What happens to the material after placement Use demonstration to evaluate opportunities to resolve issues

24 Mobile Bay Channel Open Water Thin-Layer Disposal Summer of 2012 Exercised emergency action in permit Placed 9 MCY in pre-established historic open water disposal areas Disposal Areas 1-3, 10,11 and 13 Utilized hydraulic cutterhead dredge Thin-layer disposal techniques Significant savings in dredging costs Used as demonstration to monitor and model behavior

25 THIN-LAYER PLACEMENT MONITORING Sampling conducted September 2012 Collected sediment profiling imagery at 219 stations Collected push cores for grain size analysis and geotechnical properties at about 185 stations TLP stations represented time series from 24 hours to 6 months postplacement Also included natural bay bottom

26 Sediment Profiling Imagery 27 CM 15 CM

27 OLDER DREDGED MATERIAL SPI IMAGED 09/26/2012

28 SEDFLUME

29 LTFATE Modeling Approach Current- and wave-induced sediment transport was simulated in Mobile Bay for the following conditions: Seasonal Event: Feb May 2010 Storm Events Hurricane Gustav: Aug Sep 2008 Hurricane Ida: Nov 2009 These three simulation periods were modeled with project conditions and without project conditions. The with project conditions assumes that 12 inch thick TLP deposits were placed evenly in the designated disposal areas. The without condition (base case) assumes that no TLP was placed and the sediments at the disposal sites are native (with corresponding erosion rates).

30 Modeling Conclusions Approximately 35% of the sediment that erodes from the designated disposal areas is transported and deposits in the navigation channel. The remaining 65% is widely dispersed throughout the bay by wind-, river-, and tide-driven currents. The dredge material placed in thin-layers is less erodible (~ 45%) than native sediment. Sediment becomes remobilized into Bay s natural sediment system (Not transported along the bottom)

31 Implementation Based on monitoring & modeling results IWG recommended Corps pursue modification of Mobile Harbor WQC to include a long term open-bay thin-layer disposal option WQC modified in June ,000 cy placed Summer million cy placed - Fall 2015 Surveys show material is barely detectable Developed thin-layer placement strategy Each 2-mile reach has 3 open water placement areas adequately sized based on the historic shoaling rates Cutterhead dredge used every 12 to 24 months Placement sites used every 4 to 6 years

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33 Establishment of Long Term BU Site in Upper Mobile Bay IWG Activity Potential Long Term Beneficial Use Sites in Upper Mobile Bay Low Priority 700 Acres Medium Priority 780 Acres High Priority 1,200 Acres Interagency Working Group to help plan and implement semi-contained, large scale open water disposal area (tidal marsh) in upper 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 Develop feasibility level BU design Planning process to include NEPA coordination, design, and permitting actions. Identify and prioritized potential sites Activities completed - Hydrographic survey of the upper Bay - SAV survey - Cultural resources survey Geotechnical surveys next step Pursue RESTORE Funding

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36 RESTORE Submittal Submitted to RESTORE Federal Council Bucket 2 Funded Priority List as required by Act Council consists of five Gulf States and six Federal agencies Each state gets 1 vote Federal agencies get total of 1 vote Rigorous evaluation process Science Environmental Compliance Budget RESTORE Criteria Public Review Made Funded Priorities List Council to vote to accept recommendation of staff and steering committee 12/9/15 36

37 RESTORE Proposal Goals and Objectives Restore and conserve habitat Approximately 1,200 acres of estuarine tidal marsh Enhance utilization of navigation maintenance sediment and maximize use of dredge material for sustainable coastal restoration Placement of material from Mobile Bay navigation project Federal navigation channel ASPA terminals Local and private dredging activities Construction of semi-submerged containment area and placement of dredge material Secondary Objectives Improve water quality and provide habitat for living coastal and marine resources Enhance community resilience by providing buffer to main thoroughfare Enhancing the regional economy by providing cost effective disposal options for navigation related industries located along the inland waterways 37

38 Project Implementation Phase 1 - Planning Geotechnical investigations of prioritized area Determine final footprint Preliminary design Environmental compliance and NEPA documentation Regulatory permitting Phase 2 Construction (not part of initial funding) Construction of containment feature Using material from onsite or dredged stockpiles along the BWT Initial 100 acres of marsh Using material from upper Bay maintenance 38

39 Funding Process Working through process of Interagency Agreement February/March timeframe $2.5 million 2 years Opportunity to request construction funds upon completion of Phase 1 39

40 Additional IWG Recommendations Airport Hole - Short term - Similar to Brookley Hole - Used as monitoring control Use of Dredged Material to Fill Oyster Holes - Short term - National RSM Study 40

41 Realized Benefits 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 opportunities Implementation of environmental restoration alternatives

42 Thanks! Questions? Larry Parson U.S. Army Corps of Engineers, Mobile District Planning and Environmental Division Coastal Environment Team 42