# Presentation: 537963

## SHIP SHOAL - WHISKEY ISLAND WEST FLANK RESTORATION (TE-47) 

**PPL 12**
**Coop.  Agreement ****	****EPA/DNR **
**30% E&D Review                               ****	****November 2004**
** ****Recommended to ****	****proceed to final**

**Notes:**
Approved under PPL 12
Developed under cooperative agreement between EPA/DNR
30% E&D completed in November 2004
Sponsors recommend the project continue to final design

## Project Goals and Objectives

-  Feasibility of mining Ship Shoal
-  Restore West Flank Dune, Intertidal, and Supratidal Habitat
-  Reduce wave and tidal energies to the bay
-  Add sediment to system

**Notes:**
Typical objectives of Barrier island restoration project including:
	- Restore habitat
	- Protect bay from wave energies and storm surge
	- Add sediment to long-shore transport
Main purpose – pilot project to test feasibility of mining SS for coastal restoration.

## Project Location

*Ship Shoal*

*Port Fourchon*

*Atchafalaya Bay*

*Caillou Bay*

*Terrebonne Bay*

**Depth**
**(ft, MSL)**

*Timbalier Bay*

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
Island is approximately 17 miles SW of Cocodrie
Ship Shoal – Borrow site – is approx 10 miles S-SW of Whiskey Island

## Historic Evolution: Island Retreat

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
This figure shows historic evolution since the mid 1850’s.
Isles Dernieres is considered one of the most rapidly deteriorating barrier shorelines in the US.
Whiskey Island has experienced some of the largest erosion rates measured in coastal LA over the last 100 years, 56 ft/yr. 
Moreover, in recent years (1988-2002) the shoreline recession rate has increased to 86 ft/yr, with an alongshore range of 48 to 140 ft/yr.  
Higher erosion rates were measured at the east and west flanks of the island.
Whiskey Island has lost more 20 acres per year over the last 30 years.
Without extensive restoration, the west flank and possibly the rest of Whiskey Island are expected to disappear in the next few decades.

## Whiskey IslandWest Flank

- Project Area

- Nov. 7, 2002 Aerial

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
Whiskey Island
Conceptual project was to restore the West flank of WI.

## Geotechnical Investigation of Ship Shoal

- Geotechnical Investigation of Ship Shoal

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
35 vibracores were performed across within an approximate 36,000,000 square foot area of the middle to southern half of Block 88.       The vibracores were spaced at approximately 1100 feet in the east-west direction and 1300 feet in the north-south direction. 
Water depth at the vibracore locations ranged from 18 feet (majority of the investigated area) to 23 feet (at the northeast corner of the investigated area).
Based on these investigations a 5000 foot square borrow pit within Block 88 has been identified as an appropriate source for compatible sand for this restoration project.
Depths range from –16 to –20 on shoal
Sand depths range from 4 to 20 feet with the majority of the sand greater than 10 ft. 
17.3 MCY within investigated area 
TE47 = ~4.0 MCY

## Sediment Suitability Analysis

- Whiskey Island Sand = mean grain size of 0.20 mm.
- Ship Shoal-Block 88 = mean grain size of 0.20 mm.
- The average *overfill factor**** ***for the material at the borrow site is 1.2, which is 20% overfill (USACE, 2003).

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
Sediment characteristics for the native beach material at Whiskey Island and the upper sand layer at Ship Shoal are similar (mean grain size 0.2 mm)
It is recommended that an overfill factor of 1.2 is used to calculate the overfill volume for this project.
------------------------------------
1 Overfill factor is an estimate of the volume of borrow material required to produce a stable unit of usable fill material with the same grain size characteristics as the native sediment.  The methodology for computing the overfill factor is detailed in USACE (2002) and consists of calculating relationships between the mean and standard deviations of the phi-scale grain size distributions of the native beach and borrow site.

The Overfill factor approach accounts for the volumetric changes that occur in the process of merging of two grain size distributions as well as the losses that occur in the equilibration of the construction template due to coastal processes.

An alternative methodology based on the equilibrium beach profile concept, and recently adopted by USACE (USACE, 2002) in addition to the overfill factor approach, was also used to develop an estimate of the required overfill volume.  This methodology suggests that additional borrow material would not be required.  This method, however, is based on a single grain size parameter whereas the overfill factor approach considers the distribution of grain sizes and spread around the mean (i.e., sorting).

## Ship Shoal 88 - Hazard Survey

**Ship Shoal 88 - Hazard Survey**

**Notes:**
168 recorded mag Anomalies
2 areas (7 anomalies) recommended for arch avoidance

## Impacts on Wave Climate

**Severe Storm Wave (southwest)**

**Notes:**
Impacts of removal of all of sand from study area (17.5MCY) shows maximum increase of approx 1’ in wave climate near borrow site and no affect on shore.

Project dredging volume includes ~4.0 mcy or ~25% of total sand available from study area.

## Proposed Restoration Habitat Areas

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
Conceptual project included restoration of only west flank.
Modeling shows flow training affects which could jeopardize the marsh lob
Hence Engineer recommends dune extension to prevent flow training

The proposed conceptual restoration template for Alternate “B” would restore the west flank of Whiskey Island through the direct creation of approximately 415 acres of new intertidal, supratidal, and dune habitat plus 134 acres of subtidal habitat.  

The project extension to the east would create approximately 85 acres of additional new intertidal, supratidal, and dune habitat plus 69 acres of additional subtidal habitat.  

Therefore, the total acreage created for the preferred alternate (Alternate “B”-Extended) would be 500 acres of new intertidal, supratidal, and dune habitat plus 203 acres of subtidal habitat.

## Conclusions and Recommendations

**Similar Grain Size**
**Average *****overfill factor***** = 1.2**
**4.0 Million Cubic Yards For Alternate “B-Extended”. **
** ****Alternative B = 6’ Dune x 300’ Wide + 200’ Wide Berm**
** ****Extension to the East Prevents Flow Training**

*30% Design Meeting: Ship Shoal-Whiskey Island West Flank Restoration (TE-47)*

**Notes:**
Sediment characteristics for the native beach material at Whiskey Island and the upper sand layer at Ship Shoal are similar             (mean grain size 0.2 mm).
Template Alternative “B” was recommended (6’T x 300’W Dune)
The proposed borrow area contains material suitable for restoration of the west flank at Whiskey Island.
Average Overfill of 1.2
Estimate needing 4.0 mcy of sand which includes dune extension to the east

## Next Steps

-  NEPA Document
- Complete E&D
-  Permits
-  Lease from MMS
-  Construction target – Spring 2006

**Notes:**
NEPA document is in draft form for the fill
MMS has programmatic EA for the borrow site
Complete the E&D within the next 3-6 months Including obtaining necessary permits
Need lease from MMS
Construction target date of Spring 2006 (because of CWPPRA funding constraints)