Town Engineer Steve Harding of Sebago Technics provided the Town Council with a report on the Casino Beach Stormwater Outfall and Watershed Study at the December 11, 2023 council meeting.  As Town Manager Matthew Sturgis explained, the stormwater infrastructure at Casino Beach has been problematic for several years.  “Historically, we have had larger storms that have hit over the years that have led us to this point that is close to failure, so it is a very high priority,” Sturgis said.  The Town first requested Sebago Technics to undergo a study in 2020, but was delayed due to the pandemic.  The study of an existing 16-inch diameter submerged stormwater outfall located at Casino Beach, a private beach located at the northeast corner of the Town, was conducted this year in order to analyze capacity issues and provide improvement alternatives to mitigate the recurring outfall failure and beach erosion.  

Harding explained that problems stem largely from increased rates of runoff from a watershed approximately 54 acres, which is then conveyed to the beach manhole in a 30-inch diameter reinforced concrete pipe out-letting through the 16-inch diameter submerged outfall.  “This reduction in pipe size and capacity creates a choke point.  When the 16-inch pipe capacity is exceeded, runoff surcharges the manhole-blowing off its cover and eroding the beach,” the study states.  Increased occurrences of high-intensity rainfall across the northeast United States, has increased flooding events and beach erosion.

Several approaches to improve the situation, such as upgrading rerouting and storage, were analyzed through field investigations and hydrologic modeling of the watershed.  However, the stormwater modeling results showed that these options did not provide a, “Feasible, cost effective upgradient storage or a diversion solution to make a meaningful reduction in flows at the outfall,” the report states.  Other options involving 30-inch diameter overflow bypass pipe on the beach were ruled out due to anticipated conflicts with ledge, depth of cover issues, and beach erosion concerns.

Harding explained that the team at Sebago Technics arrived at a recommendation to replace the existing drainage structure on the beach and the 16-inch outfall pipe with, “A 36-inch pipe that would meet the hydraulic needs of the system,” Harding said.  In addition, create a new manhole structure at the upper edge of the beach (or possibly off the beach entirely) with a rim elevation approximately 10 feet above sea level, “To provide improved flow conditions and a more substantial solution to address future sea level rise,” the study states.  By bringing the outfall pipe out and allowing a proper discharge at low tide, challenges to properly drain at high tide are mitigated.  “We think that’s going to be an easier pipe not only to maintain and install, but also if there’s a problem you can get to it and actually work with the pipe,” Harding said.  All of these measures, Harding expects, will likely be accomplished with, “Land-based equipment and not have to engage in having a barge work on the project.”

Cost estimates for the project are in the range of $450,000, which includes a 30% contingency, “Given the location of the outfall replacement project and the variables to be considered in the final design and construction of the new outfall.”  The project will require applying and receiving permits from the Town’s Code Enforcement Officer, the Maine Department of Environmental Protection, and the U.S. Army Corps of Engineers.  The Maine Department of Marine Resources would also be contacted to determine the environmentally best time of year to complete the project.

Next steps include conducting a subsurface geotechnical investigation to determine where the ledge is, how deep it is, and assessing whether or not portion need to be removed.  From that point, producing the final design, initiate permitting steps, and resolve any access rights would follow.  Sturgis said that the Town has had communications with Cape Cottage Beach Association regarding the project and are open to further feedback, “We are definitely happy to take input people.”  Sturgis said that the he looks to complete the project within the current year’s budgetary season.

Photo courtesy of Sebago Technics