Lessons Learned from Shoreline Protection Demonstration Projects in Southwest Louisiana

Transcription

1 Lessons Learned from Shoreline Protection Demonstration Projects in Southwest Louisiana Tommy McGinnis and Maggie Luent CPRA Operations Division Lafayette Regional Office State of the Coast June 01, 2018 committed committed to to our our coast coast

2 Problem Rock rip-rap structures sink into low weightbearing soils Why? Current nearshore areas are former marsh platforms Strategy 10/30/ /01/2017 Use CWPPRA demonstration projects to evaluate different alternatives along highly erosive shorelines in SW Louisiana

3 LA-0016 LA-0008 LA-0008 Bio-engineered Oyster Reef Demonstration Project Gulf of Mexico Shoreline along Rockefeller Wildlife Refuge LA-0016 Non-rock Alternatives to Shoreline Protection NE Vermilion Bay along Shark Island Recent Erosion ~50 ft/y

4 LA-0008 Bio-Engineered Oyster Reef Demo Federal Sponsor: National Oceanic and Atmospheric Administration/National Marine Fisheries Service (NOAA/NMFS) Project Engineers: Coast and Harbor Engineering, Inc. OysterBreak (OB) System Patent: Oyster Restoration Advancement Tech (ORA Tech) Distributor: Wayfarer Environmental Tech The OysterBreak System: interlocking, concrete rings Rings: 5 ft diameter x 6 in wide x 20 in tall; 2,200 lbs Total Length: 565 ft Two, 215 ft long x 42 ft wide sections with a 130 ft gap West - OysterKrete East Standard Weight OysterBreaks were installed by February 2012 Monitoring: Oct 2011 August 2016 Pre Construction to 4.5 years Post Construction

5 Bottom Rings are Flat and laid on top of a 1 ft thick Marine Mattress of crushed limestone encased in geofabric. Standard Weight OysterKrete Top Rings have pegs on the bottom that interlock with adjacent bottom rings.

6 LA-08 OysterBreaks Google Earth 10/30/2014 Tombolos OysterKrete - West Standard Weight - East MSL

7 LA-0008 Oyster Summary Std Wt OysterBreak (SW OB) Oyster accumulation was sparse, with oysters only surviving on in an intertidal zone. Subtidal oysters were killed by oyster drills. Surviving oysters had a rounded, low-profile shape, a morphology for high wave energy conditions. The only oyster reef formed on the back side of SW OB on the bottom layer of rings within an area of relatively higher elevation.

8 After 4.5 Years OysterBreak Reduced Soil Loss by 43%

9 LA-0008 Shoreline Movement ft/y ft/y ft/y ft/y ft/y

10 LA-0016 Non-Rock Alternatives to Shoreline Protection Demo Federal Sponsor: U.S. Dept of Agriculture- National Resources Conservation Service (NRCS) Request for Proposals - Span up to 500 Linear Feet of Shoreline - Design for 20 year project life - Structure cannot contact the land - Construction must take place from the water - Firms responsible for Manufacture, Installation, O&M, and Removal 17 Proposals Submitted and 4 Products Constructed 3 year Monitoring Period: 2014 to 2017 Elevation Surveys Every 6 Months Soil Volume Change Shoreline Movement Wave Monitoring: Nov 2016 to May 2017

11 LA-0016 Reference Intermediate Marsh with mix of Cattail and bull tongue as dominant vegetation. Cut bank where marsh meets the Bay. Marsh loss progresses quickly and in chunks. Base Material: 30 ft of Peat over Soft Organic Clay Shoreline Retreat: ft/y

12 Wave Attenuation Devices (WAD s) Owned by: Living Shoreline Solutions, Inc. Pyramid Shaped Structures 9.5 ft tall and 6.75 tons each Double Row Alignment, feet from the shoreline Some WADs shift or toppled as base connections failed. General alignment was maintained throughout the monitoring period.

13 Shoreline Change ft/y ~ 95% slower than the Reference Area Soil Volume Change Accumulated soil ~ 10% faster than was lost in the Reference Area

14 Wave Screen System (WSS) Integrated Shoreline Solutions, LLC WSS was placed ft from the shoreline in ~4 ft of water. Designed by Royal Engineers & Consultants to reduce waves while allowing water to pass through and beneath the screen. Double Wall of HDPE screens (perforated with 6 holes) hung down from Mean High Water to about ft above the bay bottom supported by steel pilings and framing.

15 Shoreline Change ft/y ~ 98% slower than the Reference Area Soil Volume Change Accumulated soil ~ 26% faster than was lost in the Reference Area The bay bottom accreted 0.63 ft underneath the WSS

16 EcoSystem Units Walter Marine Artificial Reefs, Inc Designed to convert wave energy to calm B water throughout the water column. 5 ft sq, 1 ft tall concrete plates stacked to desired elevation on 1 ft fiberglass pilings. 3 ft NAVD88 crest elevation in ~ 4 ft of water. Ends tapered towards the shoreline. Not long after installation, the many top plates were damaged due to contacting adjacent units. The top plates were removed and the pilings were braced with a fiberglass C-channel. The ESUs were a replacement product and had a shortened monitoring period.

17 Shoreline Change ft/y ~ 82% slower than Reference Area (-60 ft/y) Soil Volume Change ~99% slower than Reference Area Flaring towards the shoreline reduced erosion at the ends of the structure.

18 Buoyancy Compensated Erosion Control Modular System (BCECMS) Owned by Louisiana Shoreline Solutions, LLC; Primary Designer: Jansen, Inc. Wave barrier throughout the water column that articulates along the shoreline. 10 feet long Modules are 7 feet tall with a 6 feet base and 2 ft wide crest. They are composed of polystyrene foam encased in concrete. Modules are on the bay bottom and supported by 4 pin piles (2 vertical and 2 diagonal). Maintenance conducted to strengthen the plates connected to the pin piles. Connections failed on 1 of the 48 modules causing about 0.5 ft settlement.

19 Shoreline Change uy/y ~ 88.5% slower than the Reference Area Soil Volume Change ~77% slower than Reference Area Scour averaged ~ 1 ft along base of structure

20 Shoreline Protection Demonstration Project Goals All Shoreline Protection Alternatives met their project goals: - Substantially Reduced Shoreline Erosion - Substantially Reduced Wave Heights LA-0008 Gulf of Mexico Alternative Soil Volume Change Rate (yd 3 /ac/y) ( % Imp) Shoreline Change Rate (ft/y) (%Imp) Wave Attenuation (%) Cost per Linear Foot ($/LF) OysterBreaks -600 (60%) (73%) 70 $2,640 Lower (OK) -742 (50%) (71%) 62 $3,402 C Higher (SW) -253 (83%) -6.6 (86%) 77 $3,373 C Control WADs +218 (110%) -2.6 (95%) 70 $1,402 LA-0016 Vermilion Bay WSS +576 (126%) -1.8 (97%) 83 $1,495 ESUs -38 (98%) -9.1 (85%) 65 $1,242 BCECMS -504 (77%) -5.9 (88%) 81 $2,061 Reference -2, C Continuous, does not include the gap

21 Lessons Learned LA-0008: Half a foot makes a difference at Mean Sea Level. LA-0016: Products that allowed water to pass through the structure performed the best. For the Potential to Build Land: - Base Structure Elevation on Marsh Elevation - Limit Gaps in the Structure - Design the structure to be water permeable. For Demonstration Project Monitoring: - 3 years of monitoring was sufficient before areas were overwhelmed. - Topo/Bathy Elevation Surveys allow for more detailed information than shoreline movement alone.

22 LA-0016 LA-0008 Cheniere Au Tigre Breakwaters Feb 2017 TV-16 Nov 2001 Smaller Rock Breakwaters ~200 L x 30 W CAT-01 Dec 2005 Larger Rock Breakwaters ~ 280 L x 50 W OysterBreak 2 Rows at Base, 1 Row on Top WADs Double Row Vermilion Parish CIAP 2013

23 Thanks!!!!!!!!! Any Questions????? See the Final Reports for More Information LA _2017_OM_M_Final_with_Appendices.pdf LA Soon