KEY WEST, FL – The Monroe County Board of County Commissioners has taken another step to address sea level rise. On Tuesday, at its monthly meeting, the BOCC approved a contract for the Engineering Design and Permitting Services for the County’s “Sea Level Rise Pilot Project,” which is targeting two areas in the Keys that already have dealt with the effects of tidal flooding.
The project is for specified roads in the Twin Lakes subdivision in Key Largo and the Sands Subdivision in Big Pine Key. The project covers about one mile of total road length. The intent of the design is to lessen the severity of flooding and decrease predicted flood damage. The contract is with WSP USA, and is not to exceed $517,518.
“This is good news and shows the progressiveness of the County,” Commissioner Heather Carruthers said. “I don’t know many other communities that are engineering now to deal with sea level rise.”
The County already has included sea level rise adaptation efforts in six roadway or drainage rehabilitation projects since 2015. This is the first project that has been undertaken specifically to address sea level rise.
In January 2017, the County adopted an interim standard methodology for adapting transportation infrastructure for sea level rise based on the Sea Level Rise Pilot Project Report. Using this methodology, the roads in the pilot project will be raised to a target elevation that would result in residents experiencing on average fewer than 7 days of tidal flooding per year through 2040 (the lifespan of the roadwork). The elevations will differ in each area. But by using the methodology, everyone will receive the same level of relief from flooding.
It is costly to raise roads. In addition to the design and permitting fees, the construction for the pilot project is estimated to run about $3.5 million (including storm water). The Pilot Study examined raising roads to different elevations, and the associated costs of each, in order to balance the high cost of adaptation with the predicted relief from flooding at a particular elevation.
There are about 144 road miles countywide that are at risk of tidal flooding in the County’s preliminary modeling efforts using the SE Florida Climate Change Compact’s projections.
The pilot project design will include replacing passive gravity drainage through swales and trenches with an engineered storm water collection treatment and disposal system that requires pumps, generators, electricity, retaining walls and deep drainage wells. It also will require long-term maintenance. The engineered system is required because as water levels rises and cannot drain by gravity, the water needs to be collected and properly treated before being disposed.
WSP USA, Inc. anticipates the design to take about 15 months to complete. This timeframe includes a 6-month period to obtain all required permits. The construction, which will be put out to bid, will take about 12 months.
The information gained during the design of these pilot road projects will be used in the countywide roads adaptation plan to prepare for sea level rise. The solicitation to create this countywide plan for the 300 miles of County-maintained roads is being issued this month.