Whiskey Island Marsh Creation Rolling with the Punches

Transcription

1 Whiskey Island Marsh Creation Rolling with the Punches Santiago Alfageme, M&N Jerry Carroll, LADNR Brad Miller, LADNR

2 Project Location

3 Historic Island Retreat

4 Previous Restoration Project Whiskey Island Habitat Areas (Nov 2002) East Flank (TE-27) Restoration Area

5 Project Sponsors Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA) Federal Sponsor U.S. Environmental Protection Agency Local Sponsor Louisiana Department of Natural Resources

6 Project Goals To increase the longevity of previously restored and natural portions of Whiskey Island by increasing the Island s width to help retain sediment volume and elevation. Approximately 300 acres of back barrier, intertidal habitat Constructed tidal creek and pond features Dune feature to restore relatively low Gulf-side elevations Vegetate newly created marsh and dune areas

7 Design Team T. Baker Smith, Inc. (TBS): Lead project consultant Moffatt & Nichol (M&N): Coastal engineering, numerical modeling, and engineering design Ocean Surveys, Inc. (OSI): Geophysical data collection program and sediment mapping Eustis Engineering Company, Inc. (Eustis): Geotechnical engineering University of New Orleans, Department of Geology and Geophysics: Sediment Analysis Archeological Research, Inc.: Archeological resource investigation

8 Project Challenges 20-year project life without any maintenance Intertidal marsh over maximum period of time Very dynamic coastal environment Extreme erosion rates Complex physical processes (inlets, RSLR, storms, ) Mix of sandy and silty sediments Incorporating tidal creek and pond features

9 Back Barrier Marsh Design Dike lowered to +1.0 NAVD at creek Tidal Creeks & Ponds Dikes lowered to marsh elevation at demobilization Marsh Construction Elevation: +2.5 AVD88

10 Tidal Creek Section

11 Typical Primary Dike

12 Construction Quantities Construction Item Volume Area/Length Volume per Unit Area/Length Marsh Fill 2,300,000 cy 316 acres 7,300 cy/acre Primary Containment Dike (20 ft crest) Secondary Containment Dikes (10 ft crest) In-place Volume Requirements 92,000 cy 5,000 ft 18.4 cy/ft 75,000 cy 12,000 ft 6.3 cy/ft Tidal Creeks and Ponds 49,000 cy 5,800 ft 8.4 cy/ft Dune Fill 225,000 cy 13,000 ft 17.3 cy/ft Estimated Cut Volume Requirements from Borrow Area Construction Item Volume in Place Cut-to-fill Ratio Assumed Volume Required in Borrow Pit Marsh Fill 2,300,000 cy 1.2 2,760,000 cy Dune Fill 225,000 cy ,000 cy

13 Numerical Modeling: Delft3D Morphological Bathymetry (ft MSL)

14 Sediment Distribution in Morphological Model Depths 0 to 2ft from bottom 80% Silt/Clay 20% Sand 95% Silt/Clay 5% Sand 2% Silt/Clay 98% Sand Background Mixed Sediment 60% Silt/Clay 40% Sand 80% Silt/Clay 20% Sand 2% Silt/Clay 98% Sand Depths 2 to 5ft from bottom

15 Habitat Area Projections for WVA Area Estimates at Target Years (acres) Habitat TY1 TY3 TY5 TY10 TY20 Dune Supratidal Gulf Intertidal Bay Intertidal Subtidal TOTAL

16 Potential Borrow Sites

17 Excavation Layout 3,800,000 cy of Marsh Material 593,000 cy of Dune Material

18 Construction Timeline Bid opening - Dec 08 Low bidder: Weeks Marine $23M Construction Contract Jan 09 NTP Feb 09 Mobilization & Construction Start Mar 09 Completion & Acceptance Nov 09

19 Start of Marsh Fill: June 2009

20 Substantial Completion: October 2009

21 Aerial Photo: December 2009

22 April 2010 Monitoring Survey

23 April 2010 Monitoring Survey

24 Summary & Conclusions Project achieved initial restoration goals Optimization of available sediment resources Pre-excavated tidal creeks and ponds have settled below adjacent marsh areas More time needed before final assessment Marsh constructed above design and pay tolerance elevations

25 Thank you