US Army Corps of Engineers

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HSDRRS/MRL ConsiderationsBriefing to Coastal Protection and Restoration Authority Board

Thomas A. Holden Jr., P.E.Deputy for Programs and Project ManagementNew Orleans DistrictU.S. Army Corps of Engineers

27 March 2013

Thomas A. Holden Jr., P.E.Deputy for Programs and Project ManagementNew Orleans DistrictU.S. Army Corps of Engineers

27 March 2013

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Slide 2

HSDRRS MRL Orientation

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Slide 3

Updates

In March of 2012 briefed CPRAB and identified need to follow up on three items:

1. Overtopping rates above the crossover point 2. Armoring MRL above the crossover point 3. LPV 149 Tie-In to MRL

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Item 1: Overtopping for 1% Event

Along the west bank of the MRL above RM 85.5 (west bank crossover point) and the east bank above 81.5 (Caernarvon tie-in) there are isolated locations that do not meet the MR&T authorized grade or the1% HSDRRS design elevation

USACE concluded that these locations are acceptable for a positive finding for the Levee System Evaluation Report (LSER) based on:

Average overtopping rates along an entire reach

Performance capabilities of established turf

Capabilities of interior drainage

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Locations That Do Not Meet 1% HSDRRS Elevation

Slide 5

RM 85.5 West bank crossover point

RM 77.5 East bank crossover point

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Item 2: Armoring Needs

Armoring is not a requirement for a positive LSER

No authority to armor above the crossover point on the MRL

At the locations that do not meet the 1% design elevation, analysis shows that the overtopping rates for the 500 year event exceed the 0.5 cfs/ft threshold for armoring

Although overtopping rates exceed the armoring threshold, studies at Colorado State show well established turf performs well up to 4 cfs/ft

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500 yr Overtopping Rates Based on Existing Elevations

Based on 0.2% 50%CI Overtopping MR&T; assumes RM 70 to RM 85.5 constructed to 1% design elevation with EAMsOvertopping rates for 500yr event in cfs/ft

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Slide 8

Item 3: LPV 149 Tie-In to MRL Higher elevation transition tie-in from HSDRRS floodwall to MRL is necessary (from El +21.5 to

+24.0 feet)

T-wall and earthen levee tie-in options were investigated – earthen tie-in is recommended plan

Work will extend 100 linear feet up river and 30 linear feet down river along the MRL from the T-Wall

65% Design in Progress

Expect to advertise: August 2013

LPV 149 Typical Section HSDRRS and MRL Earthen Levee Tie-in

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Slide 9

Back Up

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HSDRRS-MRLMississippi River Levees provide risk reduction

Riverine Flood Event

Based on 1973 Project Flood Flowline (refined) plus freeboard

Freeboard can vary for east and west bank

Flood Control Act of 1928 (Authorized MR&T)

1% Hurricane Event

Based on storm surge, coincident river flow, and associated waves

Goal is to provide risk reduction for 1% chance exceedance

Hurricane and river flow are independent events, but both must be considered in analysis

Emergency Supplemental Appropriations Act (4th Supp. 2006) – (Authorized HSDRRS)

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Orientation - Definitions Crossover Point - The point at which the MR&T authorized design

grade is equal to the 1% HSDRRS design grade

For 2011 this is RM 85.5 on the West Bank and RM 77.3 on the East Bank

The 1% HSDRRS elevations govern downstream and the MR&T elevations govern upstream of this point

HSDRRS-MRL Co-Located - The area along the MRL where HSDRRS and MR&T coexist and HSDRRS design elevations govern

Engineered Alternative Measures - Alternative measures have been constructed to raise the levee height to the 1% elevation while still staying within the existing footprint. EAMs meet LSER requirements

Resilient Features - Construction work which will ensure the WBV-MRLs meet all applicable design and O&M requirements

Slide 11

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March 2009

• Draft “Mississippi River Levees Assessment” complete. Identified need to raise MRL for Hurricane events

January 2010

• Design Summit - experts invited to review modeling and design of 1% HSDRRS along the river

April 2010

• Alternatives to raise both east and west bank levees to meet the 1% HSDRRS design grade based on initial modeling completed in March 2009.

July 2010

• Based on design summit revised analysis for modeling waves and how they form on the river.

• Completed quality control and agency technical reviews

• Existing east bank MRL were sufficient

• Work required on west bank MRL to RM 85.5

March 2011

March 2012

• Commitment to complete further analysis on overtopping rates for east and west bank above the crossover points

• Provide SLFPA-E letter addressing several questions and concerns (April 2012)

• Completed analysis of overtopping rates

• No change to work required on MRL for 2011

Timeline

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Eastbank Crossover Point

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Westbank Crossover Point

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Slide 15

2011 Crossover

West Bank RM

85.5

East Bank RM 77.5

Total

15.5 miles 0 miles 15.5 miles

2021 Crossover

West Bank RM

89

East Bank RM 79.5

Total

3.5 miles 0 miles 3.5 miles

2057 Crossover

West Bank RM

95.5

East Bank RM 91

Total

6.5 miles 9.5 miles 16 miles

Miles of work required as crossover point moves upriver in future years

MRL Future Needs

Slide 15

85.5

95.5

77.5 79.581.5

70

91

89

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Slide 16

ISAAC EOC Briefing Mississippi River Update

West Point a la Hache

IHNC Lock

Carrollton

Baton Rouge

12.4 ft

11.3ft

12.4ft

Still Rising….

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Slide 17

Mississippi River Surge Levels from Venice to Red River

RM 302

RM 8West BayPoint a la HacheAlliance

CarroltonBonne Carre

Baton Rouge

Donaldsonville

St. FrancisvilleRed River Landing