There are three main drainage outfall canals in the City of New Orleans. These canals are a critical element of New Orleans’ flood control system, serving as drainage conduits for much of the city. Levees line the sides of the canals and floodwalls are situated on the top of each levee. The canals run south-to-north near the Orleans Parish lakefront between the Jefferson Parish line and the Inner Harbor Navigation Canal (IHNC; also known locally as the Industrial Canal). The 17th Street Canal extends 13,500 feet from Pump Station 6 to Lake Pontchartrain along the Jefferson Parish line. The Orleans Avenue Canal, between the 17th Street Canal and the London Avenue Canal, runs approximately 11,000 feet from Pump Station 7 to Lake Pontchartrain. The London Avenue Canal extends 15,000 feet north from Pump Station 3 to Lake Pontchartrain about halfway between the Orleans Avenue Canal and the IHNC.
Following Hurricane Katrina, the Corps constructed Interim Closure Structures at the mouths of the three outfall canals to provide the 100-year level of storm surge risk reduction. These structures were completed prior to the 2006 hurricane season, the first full hurricane season after Hurricane Katrina, at a cost of about $400 million.
The interim closure structures at the three outfall canals are composed of both gated structures and various pumps. These pumps move rainwater out of the canals, around the gates and into Lake Pontchartrain during a tropical weather event. The 17th Street Canal consists of 18 hydraulic pumps, 11 direct drive pumps, 14 bridge pumps, and has a pumping capacity of 9,200 cubic feet per second (cfs).
The Orleans Avenue Canal consists of 10 hydraulic pumps and has a pumping capacity of 2,200 cfs. The London Avenue Canal consists of 12 hydraulic pumps, 8 direct drive pumps, and has a pumping capacity of 5,200 cfs.
The decision to close the gates is based on predicted storm surge and water elevations in Lake Pontchartrain. Once the Corps makes the decision to lower the gates, local officials are notified. Once conditions improve, the gates will be raised as soon as possible.
17th Street Canal Seepage
The Corps continues to monitor the seepage occurring along the 17th Street Outfall Canal. Based on our assessments and continued observation, this seepage is coming through joints between the concrete and metal sheetpile component of the floodwall. While understandably disconcerting to the residents, this seepage does not threaten the integrity of the floodwalls or their ability to perform as designed. Following Hurricane Katrina, the Corps remediated the canals so that they are stronger and more robust. Additionally, with the construction of the Interim Closure Structures, these walls are no longer the first line of defense against storm surge and serve primarily as internal drainage water management. During an event, the ICS (to be replaced by the Permanent Canal Closures and Pumps this month) block surge from Lake Pontchartrain from entering the canals while the water levels within the canal are not allowed to exceed the maximum operating water level of 8 feet.
During construction, the contractor for PCCP positioned its on-site offices and parking lot at the site prone to seepage. The contractor cleared the area and added gravel to prepare the site for the trailers. With PCCP construction in its final stage, the Corps has removed the trailers and graded this area to remove the parking lot. While not causing or exacerbating the seepage, this work likely has contributed to it being more visible than in recent years. The Corps will restore this worksite to pre-construction condition before we can return it to the local sponsor by placing clay fill in the area to account for the impacts of the construction offices and parking lot. While not the reason for doing the work, it is possible that this additional layer of clay may also help with the seepage. We will continue to coordinate these efforts with the Southeast Louisiana Flood Protection Authority-East.
Questions can be directed to the Construction Hotline at 877-427-0345.