Floodwaters resulting from heavy rain or tropical storm events often trap St. Tammany Parish residents in their neighborhoods and deny emergency vehicles access to provide help. The community sought to make its coastal zone more resilient to flood events and address this public safety issue. Staff members from St. Tammany Parish, the Louisiana Department of Natural Resources, and the NOAA Office for Coastal Management worked together on a five-year strategy to utilize funds from the Coastal Zone Enhancement Program (Section 309 of the Coastal Zone Management Act) to address this need.
The first step was to build a project team of planning and permit staff members, engineers, coastal program staff members, and department heads. The project team partnered with Louisiana Sea Grant’s Law and Policy Program to conduct an inventory of existing policies, ordinances, and rules and regulations addressing hazard risk reduction, and determine any gaps that could be corrected with new or improved policies.
Louisiana Sea Grant developed a white paper that included findings from the inventory and gap analysis, and examples of actions that local coastal programs could take to enhance resilience. Louisiana Department of Natural Resources and NOAA Office for Coastal Management staff members met with the project team to review the findings and identify new policies and procedures that could be helpful. The project team decided to focus on modifying an existing subdivision ordinance to require higher elevation of roads in new developments.
The project team looked at historical surge information from Hurricane Gustav, which made landfall nearby in 2008, to determine how high to elevate new roads. They discovered that most roads at or above six feet of elevation did not flood during the event. During Gustav, the United States Geological Survey stream gauge reading at Mandeville on Lake Pontchartrain was 6.25 feet. The team looked at ADvanced CIRCulation, or ADCIRC, applications that model tides and wind-driven circulation and provide analysis of hurricane storm surge and flooding. The six- foot road elevation was equivalent to the ADCIRC water surface elevation from a 10-year storm event at that location. A road elevation of six feet would leave three inches on the crown of the road, which is passable by most vehicles.
The team decided that this change to the parish subdivision ordinance would increase the resilience of new development in the coastal zone, improve emergency response capabilities, and reduce maintenance costs long term. However, St. Tammany Parish Council members had concerns about whether the change would discourage new development. In weighing the costs and benefits of this action, the project team found the price of fill needed to elevate new roads would not be high enough to impede development. They also convinced the council members that environmental and public safety benefits outweighed any detrimental economic benefits.
After a series of council, planning commission, and public meetings, the ordinance was adopted. From start to finish, this effort took four years. Most of the outreach conducted for this project has been focused on sharing these results with other parishes in the Louisiana coastal zone and with other Louisiana coastal managers to help increase resilience efforts.
