Jefferson Parish, Louisiana: Jefferson Parish Watershed Management Plan and Balancing Water Campaign

Executive Summary

Jefferson Parish, Louisiana lies on a coastal floodplain of the Gulf of Mexico and has more water than land area. The parish is innovating to adapt to rising sea levels and more extreme flooding in the region, and created the Balancing Water Campaign to mitigate flood risk and improve its communities’ resilience. The approach to balancing water levels focuses on rethinking how to manage the impacts of stormwater and land subsidence to live with more water, while increasing natural drainage across the floodplain. The Jefferson Parish Watershed Management Plan was developed as a part of the Balancing Water initiative, to guide local decisionmakers with resilient floodplain management strategies for capital improvements, regulatory revisions, and land use, while emphasizing the use of green infrastructure and low-impact development. In addition, the parish is undertaking other complementary efforts like elevating flood-prone homes with the support of federal grants, and participating in the National Flood Insurance Program’s Community Rating System (CRS) program and a Jefferson Parish CRS Users Group to further local flood resilience initiatives.

 

Background

Jefferson Parish, Louisiana has a legacy of living with water, and increasingly with extreme flooding. The majority of Jefferson Parish is below sea level, and has more water than land area — with a total area of 665 square miles, of which approximately 370 square miles or 56 percent is water. 

Bordered by Lake Pontchartrain to the north, and the Gulf of Mexico to the south, Jefferson Parish is also divided into an East and West Bank by the Mississippi River in the northern section of the parish. The southern part of the parish is characterized by estuarine systems that lead in from the Gulf of Mexico. 

The coastal marshes, wetlands, and estuaries of Jefferson Parish contain numerous bodies of shallow water, providing nearly a quarter million acres of beneficial natural floodplain functions, such as water storage and filtration. Additionally, a levee and pump system is employed for drainage, which quickly removes stormwaters and provides immediate damage for communities. The parish has approximately 340 miles of canal waterways, drainage ditches, cross drains, culverts, and internal levee systems. This type of infrastructure and other changes to the hydrology of south Louisiana have reduced the supply of new sediment to offset the impacts of subsidence on coastal wetland loss. The subsidence rate in Jefferson Parish has become one of the highest in the world —- and continues to further increase the risk of severe flooding.

These risks are compounded by increasing threats from people and vulnerable development. Most of the population of Jefferson Parish (nearly 500,000) is in the New Orleans Metropolitan Area, which is highly urbanized, and has elevations of five feet below sea level to ten feet above sea level at higher natural ground.  

In addition, new development in the parish is occurring at record levels. According to Louisiana’s 2017 Coastal Management Plan’s Parish ProfilesJefferson Parish is home to approximately 7,000 repetitive flood loss or severe repetitive loss properties. And, as quantified by Flood Factor, there are 100,179 properties in Jefferson Parish that have greater than a 26 percent chance of being severely affected by flooding over the next 30 years — representing 64 percent of all properties in the parish.

To address these risks, Jefferson Parish has been undertaking different actions under an initiative called the Balancing Water Campaign to increase regional and local resilience to flooding and subsidence. 

 

Overview of the Balancing Water Campaign 

In 2015, the Jefferson Parish Floodplain Management and Hazard Mitigation departments created the “Balancing Water” Campaign for an updated approach to stormwater management that also addresses subsidence. Balancing Water is promoting a modification to the parish’s drainage system that would balance the storage of stormwater with the pumping of stormwater. Allowing some water to soak into the ground and fill the soil with moisture slows down the rate at which land subsides. Through the campaign, the parish proposes to “retrofit traditional infrastructure and to reshape existing undeveloped areas in ways that embrace the diverse landscape of Jefferson Parish.”

 

Jefferson Parish Watershed Management Plan 

As of 2021, Jefferson Parish has developed a new Watershed Management Plan as one part of the Balancing Water Campaign to bring both environmental and social benefits of sustainability and resilience to more extreme storm and flood conditions occurring in the region. The plan is based on an assessment of flooding impacts in the area watersheds that often incorporate future rainfall and sea-level rise scenarios, including some influenced by climate change. 

The plan includes comprehensive recommendations for mitigating flood loss damages from these projected environmental changes and future development. A framework of strategies to facilitate the plan’s implementation are categorized by focal areas for capital improvements, regulatory revisions, and land use. Across all focal areas, the parish emphasizes the use of green infrastructure strategies for the community or an individual property owner to encourage more low-impact development methods to decrease floodwater and runoff volume, while providing substantial environmental and community benefits well into the future. 

The parish consulted with FEMA coordinators in scoping the specific hydrologic and hydraulic analyses most relevant to the Jefferson Parish watershed. Based on FEMA-recommended criteria, the Watershed Management Plan presents an analysis of the existing and future conditions of flooding on over 50 percent of the parish inside the levees for 10-year, 25-year, and 100-year storm events using a hydrograph approach. 

Jefferson Parish participates in FEMA’s National Flood Insurance Program (NFIP) and Community Rating System (CRS) program. The Watershed Management Plan was designed to meet the requirements for the CRS’s Activity 450: Storm Water Management. The parish utilized the FEMA publication, CRS Credit for Stormwater Management, 2020 to guide the development of this plan. The objective of stormwater management, as described in the CRS guide, is “to prevent future development from increasing flood hazards to existing development, to protect existing hydrologic functions within the watershed, and to maintain and improve water quality.”

The Watershed Management Plan is a Louisiana Silver Jackets product. Since 2015, the Louisiana Silver Jackets team has been composed of federal and state government representatives from agencies like FEMA, the U.S. Army Corps of Engineers, and the Louisiana Coastal Protection and Restoration Authority to increase efficiency across different levels of government to develop more comprehensive solutions to floodplain management. MSMM Engineering, LLC was also contracted by the U.S. Army Corps of Engineers to assist Jefferson Parish in developing this plan to conform with the standards established by the NFIPm, CRS Credit for Stormwater Management.

Recommendations

The Watershed Management Plan recommendations are based on flooding impacts identified through modeling existing and future conditions, along with the flood mitigation features and program management needs to ensure the resiliency of the parish’s stormwater control systems. Additionally, some recommendations from FEMA’s CRS Credit for Stormwater Management criteria were included to support adaptation to flooding in Jefferson Parish. Many of the recommendations are already in the process of being implemented, and others are complementary to existing flood management programs.

The recommendations are offered in the categories of: Capital Improvement Program, Regulatory Revisions or Reinforcements, and Land Use Identification Modifications, and are listed below. The plan further explains and validates each recommendation as specific to Jefferson Parish. 

Capital Improvement Program 

  1. Increase the capacity of pumping systems and generator systems.
  2. Expand the use of Pump-to-the-River strategies.
  3. Maximize the use of low-impact development facilities.
  4. Ensure the capital improvements plan incorporates future development and redevelopment.
  5. Work with state and federal partners for external levee system maintenance and upgrades.
  6. Consider opportunities to advance compartmentalizing polders.
  7. Plan for increased flood protection to a 500-year standard.

Regulatory Revisions or Reinforcements 

  1. Stormwater Management Regulation Revisions.
  2. Consider storm impact mitigation and fill prohibition including controlling the volume of runoff to pre-development conditions for the 10-, 25-, and 100-year storms in design criteria ordinances as part of storm impact mitigation.
  3. 100-year design storm using NOAA Atlas 14.
  4. Private detention/retention inspection and authority.
  5. Adopt qualifying ordinances that prohibit development, alteration, or modification of existing natural channels.
  6. Provide a dedicated funding source for implementation of the watershed management plan.
  7. Incorporate municipalities into watershed planning
  8. Perform periodic updating of the watershed master plan to ensure the plan is no more than five years old.
  9. Continue and enhance community outreach educating residents of the importance of flood insurance and proactive measures property owners can take to reduce community flood impacts.

 Land Use Identification Modifications

  1. Parks and Recreation facilities (Identify parks and recreation facilities that can be designated as stormwater mitigation areas.)
  2. Wetlands and Open Space areas (Identify existing wetlands or other natural open space areas that can be preserved so that natural attenuation, retention, or detention of runoff is provided.)

Regulatory Controls

The Watershed Management Plan integrates both land use and environmental planning in order to address flooding and stormwater impacts. The quantity and rate of stormwater runoff is increasing across Jefferson Parish, along with new development, which compounds these flooding vulnerabilities. Better storage, monitoring, and management of stormwater runoff can be supported through land use and stormwater regulations that maintain the hydrologic cycle, and focus on preventing the increased risk of flooding in the future. As described in the plan, a common approach to maintaining the hydrologic cycle is to specify that post-development infiltration of a site must be equal to the pre-development infiltration, for example.

Another important watershed management strategy and priority recommendation is to improve the resilience of the Hurricane Storm Damage Risk Reduction System (HSDDRS) to a performance rating of greater than the 100-year storm event for the parish’s area levees. The HSDRRS is designed to protect the Greater New Orleans area from the 100-year or one-percent-annual-chance flood. FEMA specifies that all levees must have a minimum of three feet of freeboard against one-percent-annual-chance flooding to be considered a safe flood protection structure. The HSDRRS meets the FEMA freeboard requirement, but does not yet incorporate 500-year storm models.

Green Space and Infrastructure

The Catouatche Polder within Jefferson Parish has predominant resilience to flooding due to extensive wetland coverage. The U.S. Fish and Wildlife Service, National Wetlands Inventory shows approximately 9,700 acres of freshwater forested/shrub wetlands and 1,800 acres of freshwater emergent wetlands in the Catouatche Polder, with only 11 percent impervious surface. Jefferson Parish  also has 43 parks that provide open spaces with typically low impervious cover and in many cases, provide some detention value to the overall drainage network.

While the Watershed Management Plan was developed based on the CRS accreditation criteria and guidance, the CRS does not actually use the words “green infrastructure” due to the wide interpretation given to this term. However, the CRS does provide credit for green infrastructure design generally, such as protected open space corridors or connected riparian networks that maintain natural ecological processes and water supply. In the plan’s recommendations, the wide array of “green” strategies are narrowed to principles consistent with CRS stormwater management goals.

 

Additional Resilience Efforts

In addition to the plan, the parish is also undertaking additional complementary resilience measures under or a part of the Balancing Water Campaign.

Adaptation Strategies

In 2021, Jefferson Parish received $11.2 million from the Federal Emergency Management Agency (FEMA) to renovate or elevate 69 flood-prone homes.1 This will continue to fund an existing flood mitigation program in which homes facing repetitive flooding can be raised two feet above base flood elevation. The funding covers costs inclusive of site preparation, design, permitting, construction, and inspection. Approximately 1,500 homes have already enrolled and were elevated. This approach allows for these residents who participate in the program to remain in their homes and live with the water, rather than relocate, or try to continue to keep water out entirely.  

There are region-wide structural adaptations that also bolster resilience to flooding by moving the water. As described in the Jefferson Parish Stormwater Watershed Management Plan, the protection system in the Greater New Orleans area includes levees, floodwalls, floodgates, outfall canals, locks, surge barriers, and pump stations. “A perimeter levee system protects the area from the coastal surge and Mississippi River flooding. Pump stations are located along the perimeter levee to discharge local runoff into the exterior lakes or the Mississippi River. Local pump stations perform the same function along interior levees and discharge to marshy areas designated to collect flood water from developed areas.”

Jefferson United Mitigation Professionals Users Group

Jefferson Parish, including the City of Gretna, City of Harahan, City of Kenner, City of Westwego, and the Town of Jean Lafitte participate in the Community Rating System (CRS) and the Jefferson United Mitigation Professionals (JUMP) CRS Users Group.  JUMP has developed a Multi-Jurisdictional Program for Public Information (PPI), which serves as an official strategy for education and outreach for the residents of Jefferson Parish across jurisdictions to face flooding hazards in an informed, united fashion. The better access residents have to information about flooding vulnerabilities and mitigation strategies, the more they can prepare and to take actions to reduce their risk and bolster resilience.

 

 

Publication Date: May 20, 2022

Related Resources:

Sectors:

Resource Category:

Resource Types:

  • Adaptation plan
  • Organization

States Affected:

Impacts: