The first report by an expert scientific panel convened to answer questions about using river sediment diversions to rebuild the coast focuses on a central issue:  The inherent uncertainties in these historically unprecedented projects.

The report released Wednesday makes 18 recommendations for the state Coastal Protection and Restoration Authority to consider as it moves forward. The 50-year, $50 billion Master Plan for the Coast features at least a half-dozen large diversions south of New Orleans.

The panel acknowledged the “complexity of the science and engineering” and the lack, to date, of engineered diversions big enough to use as models. In the panel’s words, the uncertainties are “a highly relevant and pressing topic for consideration.”

“Addressing uncertainty in impact assessments and building uncertainty into model outcomes is necessary not only for determining the potential effectiveness of diversions, but also for developing operational strategies and managing expectations in the future,” the report said.

The panel also stressed the state’s need to do research that will reliably anticipate impacts on the environment as well as on “management endpoints” — a reference to the fishing industry.

The most vocal opposition to diversions has come from fishers concerned that rerouted river water will reduce salinity near the outflow of diversions and relocate their target species. Some researchers also have raised questions about the land-building ability of the diversions — whether it’s enough to outpace sea-level rise and subsidence in the area.

The panel met for the first time last month and heard from a wide range of state and federal agencies and environmental groups as well as diversion opponents.

Its next meeting is April 30 at the Lindy C. Boggs International Conference Center in New Orleans.

Recommendations for addressing the uncertainties are categorized by varying time frames, such near-term, long-term, as well as whether they are ongoing or project-specific. The recommendations fall into six general areas:

Bob Marshall

From 2013 to 2017, Bob Marshall covered environmental issues for The Lens, with a special focus on coastal restoration and wetlands. While at The Times-Picayune, his work chronicling the people, stories...