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Modeling by the U.S. Army Corps of Engineers shows it is possible to mine the ebb shoal of Big Sarasota Pass to renourish Lido Beach without a negative effect on the natural sys- tem that delivers sediment to Siesta Key, the Corps of Engineers says in its long-awaited report on the proposed $22 million Lido Beach Renourishment Project. The report's executive summary adds that the modeling demonstrated that the volume of sediment transported to the downdrift beaches "will not be affected because addi- tional sediment is brought into the system that had been immobile within the ebb shoal at Big Sarasota Pass." Further, the draft report released by the Corps of Engineers late on the morning of June 11 says Big Pass' ebb shoal has 23.3 million cubic yards of sand. The Corps of Engineers proposes to mine 1.3 million cubic yards, or about 6 percent, of the sediment from that shoal for the first renourishment in a 50-year- long project on which the agency is working with the City of Sarasota. The ebb shoal grew about 2.3 million cubic yards between 2004 and 2013, the report continues. The yearly accretional average between 1991 and 2013, it notes, was 113,000 cubic yards per year. The report explains that the Corps of Engineers staff in Jacksonville undertook multiple 1.5-year model runs to understand better how mining the Big Pass ebb shoal would potentially change the structure of the shoal over a longer period. Limitations in computer memory, processing speed and model capability meant the maximum model duration was less than two years, the report points out. "Results became less detailed and smoothed over time," it says, making them of "limited use for understanding fine-scale [structural] change and heterogeneity within the shoal." The Corps of Engineers' Jacksonville staff also examined the renourishment history of Lido Key and the introduction of sediment from offshore sources into the system to determine whether any correlation existed between the renourishment volume and ebb shoal growth, the report points out. The results showed the ebb shoal is accreting at a greater volume than represented just by the volume of sand placed on Lido Key. Therefore, the report says, "[N] ourishment volumes at Lido Key alone cannot explain the growth of the ebb shoal." Nonetheless, the report does note that the renourishment projects on Lido contrib- uted to the growth of the ebb shoal over the past decade. The executive summary also points out that modifications of Lido Key in the 1920s led to many of the present issues involving the island, "including the accelerated ero- sion from the southern shoreline," as well as "channel pressure on the northern interior shoreline of Siesta Key" and "ensuing erosion of the northwestern beaches of Siesta Key." MINING THE EBB SHOAL OF BIG SARASOTA PASS SHOULD HAVE NO IMPACT ON THE NATURAL SYSTEM THAT DELIVERS SEDIMENT TO SIESTA KEY, THE U.S. ARMY CORPS OF ENGINEERS SAYS By Rachel Brown Hackney Editor Sarasota News Leader June 13, 2014 Page 10