Corps Offers Plan To Raise Nola Levees
According to a pair of reports released December 9 and published in the Federal Register December 13, the U.S. Army Corps of Engineers is proposing spending about $3.2 billion on the New Orleans area’s Hurricane and Storm Damage Risk Reduction System (HSDRRS) over the next 50 years to combat “consolidation, settlement, subsidence, sea level rise and new datum” which could otherwise render the system insufficient to protect against a 100-year storm (or one that has a 1 percent chance of striking the area in any given year). The Corps built the HSDRRS system, at a cost of more than $14 billion, after Hurricane Katrina flooded much of the greater New Orleans area in August 2005.
Levees and floodwalls within the system were built to meet the height needed to provide protection from a 100-year storm beginning in 2011. However, due to the sandy soil in the New Orleans area, settling within the system began immediately after construction was complete. Furthermore, because the system was built over a period of time, settling varies throughout the system. What’s more, the original HSDRRS authorization did not provide for future levee or floodwall lifts, thus the extensive need for levee lifts and floodwall modifications.
In the two General Re-evaluation Reports, the Corps outlined its Tentatively Selected Plan (TSP) for “system-wide periodic levee lifts, floodwall modification and floodwall replacement to the projected 100-year level of risk reduction through the year 2073.” The two reports cover the Lake Pontchartrain and Vicinity (LPV) project and the West Bank and Vicinity (WBV) project, which collectively comprise the HSDRRS.
For LPV, the Corps is proposing lifts along 50 miles of levees along the existing levee alignment, along with 18.6 miles of floodwall modification and replacement. The LPV TSP also includes targeted foreshore protection measures. The total estimated cost for LPV during the life of the plan is $2.6 billion.
For WBV, the TSP calls for 65.6 miles of levee lifts along the existed levee alignment, with 0.8 miles of floodwall modifications and replacements, at a total estimated cost of $600 million.
The Corps will hold multiple meetings in January 2020 to receive public comments on the two proposals. The agency is also receiving written comments through February 7, 2020. Comments should be sent by mail to U.S. Army Corps of Engineers, New Orleans District, c/o Bradley Drouant, P.E., CEMVN-PMO-L Room 361, 7400 Leake Ave., New Orleans, La. 70118. Comments may also be submitted by email to CEMVN-LPVGRR@usace.army.mil for LPV-related comments and to CEMVN-WBVGRR@usace.army.mil for WBV comments.
The final report is expected in the latter part of 2021. The TSP spans a 50-year period between 2023 and 2073. The timing is significant, with the New Orleans area flood protection system up for recertification in 2023. Certification of 100-year flood protection directly impacts flood insurance rates within the system.
The LPV project is spread across the parishes of St. Charles, Jefferson, Orleans and St. Bernard—all between the east bank of the Mississippi River and the south shore of Lake Pontchartrain. LPV ties in with the Mississippi River and Tributaries (MRT) levee project at the west and east ends of the system, with the MRT protecting the area from riverine flooding.
The Corps calculated a benefit-cost ratio for the LPV project of 2.6 to 1. Based on current data for levee subsidence, the LPV TSP calls for 11 lifts along 17 miles of levees from 2023 to 2033; four lifts along 24 miles of levee between 2023 and 2043; 15 lifts along 61 miles of levee between 2044 and 2053; and three lifts along 6 miles of levee between 2054 and 2065. The Corps will lay out a plan for floodwall modification and rebuilds in its final report in 2021.
The WBV project is spread across the parishes of St. Charles, Jefferson, Orleans and Plaquemines and includes perimeter levees and floodwalls to the south, “co-located” river levees on the west bank of the Mississippi River where the river levee provides dual protection from riverine flooding and storm surge inundation, and interior levees and floodwalls on the Harvey and Algiers canals.
The Corps notes that the new design to meet 100-year protection through 2073 increases the area where the WBV levee coincides with the MRT levee and moves the “crossover point” for the HSDRRS and the MRT levees upriver 10 miles from Mile 85.5 to Mile 95.5.
The adjustments are due to both anticipated subsidence within the system and a mid-level forecast for sea level rise in the next 50 years.
The Corps anticipates a benefit-cost ratio for the WBV project of 2.4 to 1.
The two General Re-evaluation Reports and associated Environmental Impact Statements were authorized in the Water Resources Reform and Development Act of 2014. The studies are in partnership with the plan’s non-Federal sponsor, the Coastal Protection and Restoration Authority Board of Louisiana (CPRA). The non-Federal sponsor will bear 35 percent of the total project cost, though that burden will be shared among the area’s flood protection authorities and levee districts.
For more information on the studies or to view the reports, visit the New Orleans District’s website at mvn.usace.army.mil and search “LPV” or “WBV.”