PHILADELPHIA (September 26, 2017) – Today the U.S. Army Corps of Engineers’ Philadelphia District posted this update on its ongoing temporary mitigation measures related to storm water management in the City of Margate, N.J.:
OVERALL PROJECT PURPOSE. Work is part of the Absecon Island storm damage reduction project, which involves building a continuous dune and berm system for Atlantic City, Ventnor, Margate, and Longport, and constructing two new seawalls along with rebuilding the historic Atlantic City boardwalk along Absecon inlet. When complete, this project—the result of a partnership between the New Jersey Department of Environmental Protection (as non-federal sponsor) and USACE—will greatly reduce the risk of damages from coastal storms for all four municipalities.
INTERIM MEASURES FOR STORM WATER MANAGEMENT. After severe rainfall at the end of July 2017 (more than 5 inches fell on Margate in less than 24 hours) brought about excessive and persistent ponding behind the dunes, the Corps took action to address and fix this problem.
- Within the next few weeks we designed and installed a series of interim measures to improve drainage from the city’s pre-existing storm water management system.
- Concurrently, we began working with NJDEP and the City to develop an alternative long-term storm water management design, consisting of a manifold system and outfalls, to be constructed at full federal expense.
- The interim measures, which include the use of sump basins, temporary outfall pipes, and pumps when necessary, are in place north of Nassau Avenue—as they can only be installed where the dune and berm are complete. To date, we have installed three temporary outfall pipes. As construction progresses through Margate, we will add the interim measures within each subsequent completed section.
- Within the active construction area—currently Nassau to Rumson Avenue—we have been (and will continue) pumping as needed to ensure no significant ponding remains after any rain or high tide event.
- Through two recent 2-inch-plus rain events in early September, the systems in place functioned as designed and no significant standing water remained after either of those events.
IMPACT OF HURRICANES JOSE AND MARIA. In anticipation of high tides and waves coming in from Jose last week and potentially from Maria this week, dredging operations had to be halted for safety and all beachfill operations are on hold.
- The Corps made ready all available pumps onsite and attempted to protect the temporary drainage outfalls south of Iroquois Avenue by building up a dike of sand in front of each, as backflow preventers to be installed in the pipes had not yet been delivered.
- However, on Sept. 19 the extreme tides and waves associated with Jose broke through, pushing water back up through the temporary pipes to pond behind the newly constructed dunes.
- The surge and waves at the shoreline pushed the water level up over the berm, at an elevation (7.25 feet above mean sea level) significantly higher than the street end scuppers (bulkhead drain openings) throughout Margate. This increased ponding in the active construction zone and behind the temporary outfalls, as the pipes had filled with sand, and would not allow the water to drain back out as the tide receded. We were, however, able to pump down the water the following day.
- As the waters rose above the level of the scuppers, this caused widespread flooding of the streets and ponding on the beaches well south of the active construction area. But north of Iroquois Avenue, where the dune and berm were complete and backed-up temporary outfalls were not an issue, there was no significant street flooding noted.
GOING FORWARD. At this point the installed temporary outlet pipes have been cleared of sand or will be within the next few days.
- Until the backflow preventers are installed, we will employ temporary gates on the seaward end with temporary plugs on the intake end behind the dunes to block the pipes during elevated tides.
- With elevated storm tides forecast to persist over the next two weeks, likely to cause further intermittent ponding behind the dune, we will continue to pump out water when and where necessary. (In some areas south of Iroquois, elevated groundwater levels may slightly delay pumping until the groundwater table returns to normal.)
- North of Iroquois, groundwater will fill the sump system, resulting in only minor ponding until the pumps kick on, removing the water that accumulates above the water table to the ocean.
- USACE and its contractors are working this situation 24/7. We remain committed to adaptively managing these storm water challenges within Margate until the coordinated long-term storm water management solution is installed.
- Our engineers have been working with the City and NJDEP on design aspects of that system, which will include collection basins near each street-end bulkhead, tied together with a lateral manifold system carrying the storm water out to the ocean through outfall pipes. (This type of system is commonplace throughout many New Jersey oceanfront communities.)
- USACE continues to prioritize finishing construction of this dune and berm system, so that it can begin fulfilling its intended purpose of helping protect the people and properties of Margate and its Absecon Island neighbors from storms such as Sandy, Harvey, and Irma, or the many unnamed nor’easters that routinely visit New Jersey’s coastline.
Release no. 17-024