Consultant finalizes critical Big Pass dredge analysis

A county-ordered peer review of the proposed dredging of Big Pass states the U.S. Army Corps of Engineers has not provided enough verifying documentation to demonstrate the controversial project should move forward.

The Army Corps, in tandem with the city of Sarasota, is working on a long-term plan to renourish eroded portions of the Lido Key shoreline with sand from Big Pass, which has never before been dredged. That proposal has been met with concern from county officials and residents on Siesta Key, worried about the project’s impacts on the island to the south.

In April, the county hired coastal engineering firm Atkins to conduct a third-party analysis of the project. After releasing a draft of the report last month, the consultant submitted its final report today.

Although the analysis does not provide a conclusive statement on whether Siesta Key would be impacted by the project, it does state definitively that insufficient evidence exists to address the county’s concerns.

“The report documents no adverse impacts,” the report states of the Army Corps-provided information.” However, the deficiencies in the documentation of the data and model create uncertainty in this regard.”

"The report documents no adverse impacts; however, the deficiencies in the documentation of the data and model create uncertainty."

The report is frequently critical of the Army Corps’ supporting evidence. On several fronts, Atkins suggests the project needs more modeling or updated data before it can be safely concluded the dredging will do no harm. Questions pertain to plans for two sand-retaining groins on Lido Key, the source of the sand in the Big Pass ebb shoal and the historical environmental data used in the models.

Atkins believes there is a higher degree of risk because the sand for the project would be “back-passed” from a southerly source. Most renourishment efforts use sand from a source that would follow the natural path of sediment movement — which, in the case of Lido Key, would necessitate a sand source to the north.

Although the report supports some renourishment effort for Lido Key, it does not agree with the Army Corps’ conclusion that no other sand source could be located. Because the proposed dredging would be the first step in a 50-year renourishment effort, Atkins suggests a different sand source could be used initially as the Army Corps works to bolster its data.

“We recognize the need to nourish Lido Key and believe that there are ways to provide an intermediate nourishing while studies are validated or, if needed, additional studies implemented,” the report states.

Even if the Army Corps is able to provide the requested verification, the report suggests an alternative sand source should be used for renourishment — or at least a smaller amount of Big Pass sand than the proposed 1.3 million cubic yards.

City and county employees were unavailable for immediate comment on the report. City Engineer Alex DavisShaw was skeptical about the lack of specifics present in the draft report, but said she would hold off on any response until Atkins released its final report.

If the project moves forward with the requested data, Atkins recommends close monitoring of how the renourishment impacts the sediment transport system. If the Army Corps moves ahead without providing the requested data, Atkins encourages the creation of predefined mitigation plans and funding sources in case something goes awry.

“Without those assurances, we recommend that the county should consider actions to hold a responsible entity accountable for activities that directly or indirectly result in impacts,” the report states.