CEPD provided details on beach renourishment
The Captiva Erosion Prevention District was recently presented with the engineering design, storm damage benefits and projected costs of the island’s upcoming beach renourishment project.
At the June 13 regular meeting, APTIM Coastal Planning & Engineering outlined the “2018 Engineering Design and Storm Damage Benefits” report on the 2020-2021 project for the district’s commission. Since 1988, similar on-island projects have taken place about every eight years.
Thomas Pierro, director of operations for APTIM, pointed out that renourishment projects along Captiva’s beaches date back even further, with limited fill placements done in 1961 and 1981.
“This program has been in place for over 50 years,” he told the commissioners.
The most recent project took place in 2013 from October to December. Designed to address background erosion and traditional hotspot areas, it entailed a total of 965,000 cubic yards of sand placed over six miles of shoreline on Captiva and Sanibel – part of an interlocal agreement.
“This project is focusing on just Captiva Island,” Pierro said of the new project.
Since 1988, a total of 4.4 million cubic yards have been placed on the island. As of October, an estimated 2.74 million cubic yards – about 63 percent – of the sand remained on Captiva.
The upcoming project will place 900,000 cubic yards from Redfish Pass south to Blind Pass. It will benefit the same five zones as in 2013, with Zone 1 updated to extend from 1200 South Seas Plantation Road to 1141 Longifolia Court, rather than to 925-957 South Seas Plantation Road as it was before.
Pierro explained that the beaches and zones have historically been established in each study for the benefit analysis portion, which are then updated with each of the new beach renourishments.
The new project is also anticipated to last for 10 years, compared to eight years.
According to Pierro, the last project was “federally authorized,” which meant following guidelines involving a 40-foot berm and beach footage. Because the new project is not, he noted that the CEPD can try to fix three erosion hotspots – Zones 1, 3 and 5 – identified by the study with the project.
“We can put some sand down,” Pierro said, adding that the proposal is consist with the permit.
APTIM estimated that the construction costs for the 2020-2021 project will total $33.5 million, including 15 percent for contingency, based off of the previous projects projected and actual costs.
In addition, it will cost $2.72 million for engineering, design, administration and monitoring for nine years, for a total cost of $36.2 million. Pierro explained that the report takes into account the previous non-federal, cost sharing percentages – state and county – which were not yet finalized at the time.
With the cost share deductions, the estimated total cost for Captiva is $14.7 million.
David Swigler, senior project engineer for APTIM, outlined the storm damage benefits of the project for the commissioners. He reported that two models were used in the analysis, the U.S. Army Corps of Engineers’ Risk and Uncertainty Storm Damage Model and the SBEACH Storm Recession Analysis.
The Corps model estimates damage values in dollar amounts based on background erosion rates, storm erosion, erosion control structures and values of the upland buildings and infrastructure. The second model simulates beach profile changes during major storm events and provides storm recession values.
“We basically developed a range of storms,” he said.
Swigler reported that the estimated total storm damage without the project is $5.76 million, as compared to $3.74 million with the project – a storm damage reduction benefit of $2.02 million.
“But based on a 22-year time period,” he said.
Following questions from the commission on the numbers, Pierro explained that the $2.02 million benefit is per year over 22 years, so the total benefit of the project would be about $44 million.
APTIM anticipates having the final benefits analysis report completed by September.
A ballot referendum will go before voters on March 5 for the project; the previous ones passed.