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NEW ORLEANS—On the one-year anniversary of Hurricane Katrina, the focus is no longer just on the damage done, but also on the progress made since coastal areas of the United States, including New Orleans and Mississippi, were devastated on Aug. 29, 2005. By the start of this year’s hurricane season on June 1, 2006, the U.S. Army Corps of Engineers (Corps) had achieved at least a pre-Katrina flood- and storm-level protection by repairing and restoring 169 miles of Mississippi River and New Orleans area levees and floodwalls.

To improve the levee protection system along the coast, the Corps is raising levee heights, in some cases as much as 7 feet, and upgrading or replacing existing flood I-walls with improved designs. The Corps expects these improvements to provide 100-year protection to about 98 percent of the population in the New Orleans area.
Working with city, state, and other Federal agencies, the Corps will continue to upgrade New Orleans’ flood and storm protection through 2010. According to the Corps’ timeline, restoration of undamaged and subsided areas and previously unconstructed portions of authorized projects will be completed between June 1, 2006 and September 2007. December 2007 will mark the completion of the final technical report that analyzes higher levels of protection. In 2010, the levees’ flood protection as meeting the National Flood Insurance Program’s 100-year protection level will be certified, as well as additional improvements, such as permanent closure and pumping stations at the outfall canals; navigable floodgates to protect the industrial canal; storm-proofing of existing pump stations; selective armoring of levees; incorporating a portion of non-federal levees in Plaquemines Parish; and restoring ecosystems.

The Corps recently awarded a contract to DMJM Harris to evaluate methods to reduce demand for capacity on the three outfall canals at Orleans Ave., London Ave., and 17th Street, which currently are the primary outlets to drain rainfall from New Orleans’ streets. According to the Corps, DMJM Harris will work with officials from Jefferson Parish and the New Orleans Sewage & Water Board to explore interior drainage options, including pumping rainwater to the Mississippi River and developing temporary detention areas.

In late June, the Corps announced that it expects completion in the fourth quarter of 2006 of a detailed chronology of the "planning, economic, policy, legislative, institutional, and financial decisions that influenced the design, scale, configuration, construction, governance, and maintenance" of the New Orleans flood protection system as it existed prior to Aug. 29, 2005. "The Hurricane Protection Decision Chronology will enable the Corps and the nation to fully understand the long history of federal, state, and local decisions that led to the design and construction of the New Orleans-area flood and storm damage reduction system," said Maj. Gen. Don T. Riley, Corps director of Civil Works.

Design concerns

In addition to completed investigations sponsored by the Corps and by the National Science Foundation (see CE News, July 2006, page 12), a reconnaissance team led by the U.S. Commerce Department’s National Institute of Standards and Technology (NIST) identified the following needs:

  • credible scientific and engineering information for guiding the repair and future upgrade of the New Orleans flood-protection system;
  • risk-based storm surge maps for use in flood-resistant design of structures, including roads and bridges; and
  • evaluation of and possibly modification to the Saffir-Simpson hurricane scale’s treatment of storm surge effects due to hurricanes.

In its June report, NIST said that "existing flood hazard maps … are outdated and not consistent with the risks posed by storm surge in these coastal areas." Among NIST’s 23 recommendations for improvements to design, construction, and maintenance of coastal infrastructure is the development of risk-based storm surge maps for several mean recurrence intervals, incorporating storm surge height and current velocity and the associated wave action.

Another group of experts, assembled by the American Geophysical Union (AGU), recommended that designers of flood-control systems take into account the amount of sea level rise and subsidence expected during any structure’s design life. "As a result of subsidence," the AGU experts reported, "new Federal Emergency Management Agency (FEMA) Base Flood Elevations maps that will be available for the area in 2007 may not be accurate; yet those maps will form the basis for flood control and establish levels for rebuilding."

Meanwhile, the Louisiana Recovery Authority stated that for residents to be eligible for its State Homeowner Assistance plan, all reconstruction work must meet or exceed the latest available FEMA Advisory Base Flood Elevations (ABFE) and meet the legal requirements of the State Uniform Construction Code. FEMA previously stated that these advisories must be used for any rebuilding projects using certain FEMA grant dollars, thus the advisories apply to both public infrastructure projects as well as to mitigation grants.

In ABFEs issued in April for Jefferson, Orleans, and St. Bernard parishes, as well as portions of Plaquemines and St. Charles parishes in southern Louisiana, FEMA recommended that "substantially damaged homes and businesses protected by levees elevate 3 feet, or follow what is shown on the current effective flood insurance rate map (FIRM), whichever is higher." FEMA said that its flood-recovery guidance takes into account storm data, as well as coastal land loss, degradation of coastal barriers, and subsidence. The ABFEs, however, are interim products while new, preliminary FIRMs are being completed.

The New Orleans Community Support Foundation selected a team of planning and redevelopment experts led by Omaha, Neb.-based HDR to facilitate neighborhood-based planning efforts as part of the Unified New Orleans Plan. Fifteen teams were selected from 65 applications, and New Orleans residents participated in the team-selection process for specific neighborhoods. HDR teamed with HOK Planning Group and New Orleans-based partners Mathes Brierre Architects; communications consultants Jeanne P. Nathan of Creative Industry, Inc and CBM Group; and urban designers Wisznia Associates and Robin Riley.

HDR’s related experience includes developing renewal plans for Gulfport and Moss Point, Miss., as part of the Mississippi Renewal Forum (www.mississippirenewal.com). The Gulfport charrette helped produce a New Urbanist SmartCode, making the city one of the first in the nation to consider this customized, form-based coding, instead of conventional use-based zoning.

Bridge replacements

Highways and bridges along the Gulf Coast also were ravaged during Hurricane Katrina, resulting in the need to repair and improve portions of this vital infrastructure. Ground recently was broken for the new I-10 Twin Span Bridge, which will replace the Twin Span Bridge between New Orleans and Slidell, La. According to the Louisiana Department of Transportation and Development, it is the largest public works project in the history of Louisiana at a cost of $803 million. It is funded completely with federal money. To allow the bridge to withstand a higher storm surge, it will have an elevation of 30 feet—21 feet higher than the old bridge. The new bridge also incorporates reinforced concrete walls to increase the structure’s storm-surge resistance and to minimize effects from a barge collision. It is the first bridge in Louisiana built entirely with high-performance concrete.

The Mississippi Department of Transportation awarded a $266.8 million bridge-replacement contract to Granite Construction Company, Watsonville, Calif., in a joint venture with Archer Western Contractors of Atlanta, to replace the U.S. 90 bridge over St. Louis Bay. The design-build contract includes removal of what remains of the old bridge. Now under construction, the new Bay St. Louis Bridge will be higher—about 85 feet high at its highest point—eliminating the need for a drawbridge. It also will be wider, with four, 12-foot-wide travel lanes separated by a concrete median barrier, an 8-foot-wide inside shoulder, a 10-foot-wide outside shoulder, and a 12-foot-wide pedestrian/bicycle lane on its south side.