Louisiana Coastal Area Medium Diversion with Dedicated Dredging at Myrtle Grove Barataria-Terrebonne National Estuary Program Management Conference Meeting Study Update 11 Sept 2012

US Army Corps of Engineers BUILDING STRONG ®

Study Authority

Title VII, Sec. 7006(c)(1) of the Water Resources Development Act of 2007 (WRDA) authorizes the Secretary to carry out the following projects substantially in accordance with the restoration plan: A.

Mississippi River-Gulf Outlet Environmental Restoration at a total cost of $105,300,000.

B. Small Diversion at Hope Canal at a total cost of $68,600,000.

C. Barataria Basin Barrier Shoreline Restoration at a total cost of $242,600,000.

D. Small Bayou Lafourche Reintroduction at a total cost of $133,500,000.

E. Medium Diversion at Myrtle Grove with Dedicated Dredging at a total cost of $278,300,000.

Before the Secretary may begin construction of any project under this subsection, the Secretary shall submit a report documenting any modifications to the project, including cost changes, to the Committee on Transportation and Infrastructure of the House of Representatives and the Committee on Environment and Public Works of the Senate

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LCA Critical Needs



Prevent future land loss where predicted to occur



Restore fundamentally impaired or mimic deltaic processes through river reintroduction



Restore or preserve endangered critical geomorphic structures



Protect vital local, regional, and national socio economic resources

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Overview

The feasibility study has an overarching goal to “

Use river resources (in a combination of diversion and dedicated dredging) to increase Area 1 wetlands quantity and quality

”.

From this goal, study specific objectives were developed: 1. Establish geomorphic connection from the river to the estuary to introduce sediments to build and sustain Area 1 wetlands.

2. Deposit and retain riverine resources to maintain 33,880 marsh acres in Area 1 over the 50-year period of analysis

.

Alternatives have been developed that seek to support the study goal and accomplish the study objectives.

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Preferred

Initial Array of Alternatives

Alternatives were developed in concert with project objectives and to address problems in the study area. They represent different combinations of diversion structure size, flow regime, and marsh creation scale. Each alternative was evaluated for benefits (marsh acres) and preliminary costs.

• Alternatives represent: o Small to large diversion sizes o Restrained to aggressive flow regimes o Calendar based o Sediment thresholds o Scales of marsh creation over time • 60 alternatives met both objectives • We are carrying through the 2004 Recommendation

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Structure & Operation Alternatives

cfs

Continuous Flow through Structure Dec – May Hydrograph Dec – Mar Hydrograph Top 33% Occurrence for Sediment Top 20% Occurrence for Sediment Top 10% Occurrence for Sediment Top 1% Occurrence for Sediment Top 37.5% Occurrence for Sediment 5,000 15,000 30,000 45,000 60,000 1A 1B 1C 1D 1E 75,000 1F 2F 100,000 1G 2G

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2A 2B 2C 2D 2E 3A 3B 3C 3D 3E 3F 3G 3H 4A 4B 4C 4D 4E 4F 4G 5A 5B 5C 5D 5E 5F 5G 5H 6A 6B 6C 6D 6E 6F 6G 6H 7A 7B 7C 7D 7E 7F 7G 7H 8A 8B 8C 8D 8E 8F 8G 8H

Dredging Scales

(to be paired with a diversion alternative)

Feature Concept Description Total Acres

MC-7A MC-7B MC-7C D7-1 D7-2 D7-3 Priority Area Completion Approach – Small Scale Priority Area Completion Approach – Medium Scale 6.5mcy per dredge cycle (~946 ac created in each of 5 cycles) 6.5mcy per dredge cycle (~946 ac created in each of 8 cycles) Priority Area Completion Approach – Large Scale 6.5mcy per dredge cycle (~946 ac created in each of 13 cycles) Infuse Diversion w/ Sediment Small Scale Dredging 6.5mcy per dredge cycle (for 5 cycles) Infuse Diversion w/ Sediment Medium Scale Dredging 6.5mcy per dredge cycle (for 8 cycles) Infuse Diversion w/ Sediment Large Scale Dredging 6.5mcy per dredge cycle (for 13 cycles) 4,730 7,568 12,298 TBD TBD TBD

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Sediment Thresholds

Year 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 Number of Days/Year the 1985-2009 Tarberts Landing Discharge Reached or Exceeded the Discharge Threshold Value (cfs) 1,230,000 928,000 789,000 700,000 640,250 600,000 0 0 10 9 45 85 94 0 76 72 32 36 52 54 23 0 27 44 26 15 30 0 1 0 0 0 0 0 1 17 0 0 0 0 0 30 0 0 0 0 0 0 0 0 0 0 106 22 25 34 93 117 158 4 168 111 50 79 121 115 70 0 54 95 45 77 53 0 19 2008 2009 31 13 92 71 45 847 120 91 1,827 20 5 2

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1% 10% 20% 148 120 66 84 149 166 194 66 273 121 113 125 163 163 112 15 117 125 80 137 90 11 70 158 177 3,043 0 146 33.3% 139 62 40 63 126 155 187 36 234 117 92 105 146 147 88 0 84 115 60 107 77 5 25 153 149 2,512 1 159 27.5% 159 147 70 106 169 173 196 91 292 130 124 148 174 175 135 32 129 132 98 157 96 15 108 164 207 3,427 0 136 9 37.50% Based on a frequency analysis of the 1985-2009 Tarbert Landing Qs, the Highest 1%, 10%, 20%, 33.33%, and 37.5% discharge threshold values were determined. Annual daily discharge data were compared to those threshold values to compute the frequency of daily discharges equal to or greater than the threshold values.

= Total days > or = discharge threshold (in 25-yr record) = Number of years discharge threshold did not occur = TSS (mg/L) of discharge threshold = Frequency of discharge threshold (1985-2009 Qs)

Preliminary Screening

Screening will applied to reduce the total number of alternatives for full evaluation. This will be based on several variables including: • What are the benefits of each alternative?

• Does an alternative meet both objectives?

• Which alternatives are most cost effective?

• Which alternatives avoid constraints?

Screening is an iterative process and there may be additional criteria the PDT could develop to help further screen alternatives. The final array will hopefully consist of approximately five alternatives.

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Diversion Alternatives

cfs

Continuous Flow through Structure Dec – May Hydrograph Dec – Mar Hydrograph Top 33% Occurrence for Sediment Top 20% Occurrence for Sediment Top 10% Occurrence for Sediment Top 1% Occurrence for Sediment Top 37.5% Occurrence for Sediment 5,000 15,000 30,000 45,000 60,000 1A 1B 1C 1D 1E 75,000 1F 2F 100,000 1G 2G

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2A 2B 2C 2D 2E 3A 3B 3C 3D 3E 3F 3G 3H 4A 4B 4C 4D 4E 4F 4G 5A 5B 5C 5D 5E 5F 5G 5H 6A 6B 6C 6D 6E 6F 6G 6H 7A 7B 7C 7D 7E 7F 7G 7H 8A 8B 8C 8D 8E 8F 8G 8H

Dredging Scales

(to be paired with a diversion alternative)

Feature Concept Description Total Acres

MC-7A MC-7B MC-7C D7-1 D7-2 D7-3 Priority Area Completion Approach – Small Scale Priority Area Completion Approach – Medium Scale 6.5mcy per dredge cycle (~946 ac created in each of 5 cycles) 6.5mcy per dredge cycle (~946 ac created in each of 8 cycles) Priority Area Completion Approach – Large Scale 6.5mcy per dredge cycle (~946 ac created in each of 13 cycles) Infuse Diversion w/ Sediment Small Scale Dredging 6.5mcy per dredge cycle (for 5 cycles) Infuse Diversion w/ Sediment Medium Scale Dredging 6.5mcy per dredge cycle (for 8 cycles) Infuse Diversion w/ Sediment Large Scale Dredging 6.5mcy per dredge cycle (for 13 cycles) 4,730 7,568 12,298 TBD TBD TBD

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Draft Final Array of Alternatives

Identifier

1B (LCA 2004 Recommendation) 8F-Small 15,000 cfs 75,000 cfs 8G-Small 8H-Small 8G-Medium 8H-Medium 8H-Large

Structure Size Marsh Creation

100,000 cfs 125,000 cfs 100,000 cfs 125,000 cfs 6,286 Acres 4,730 Acres 4,730 Acres 4,730 Acres 7,254 Acres 7,254 Acres 125,000 cfs 12,118 Acres

Flow Regime

Year-Round (No Flow Below 150,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River) Sediment Threshold > 136 mg/L (No Flow Below 600,000 cfs in River)

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Next Steps

Several additional evaluation steps will be initiated to further analyze and describe alternatives. Upcoming activities include: • Hydrodynamic modeling in the Barataria Basin to determine stage, salinity, and velocity effects for alternatives • Wetland Value Assessments/Fisheries Modeling • River Modeling • Detailed Cost Estimates and Project Design • State to initiate PED phase A TSP is scheduled for May 2013 and a Chief’s Report in Oct 2014.

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Questions?

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