Researchers compare diversion, dredging plans
A new study is asking policy makers to expand their thinking about the costs and benefits of two coastal restoration techniques: diverting sediment and freshwater from rivers versus creating marshes primarily through dredging.
The research suggests marsh creation projects, though more expensive on the front end, may in some cases generate a higher benefit-cost ratio than sediment diversions over a 50-year time span, Rex Caffey recently told the state Coastal Restoration and Protection Authority.
Caffey is a professor and director of the Center for Natural Resource Economics and Policy at LSU Agricultural Center and Louisiana Sea Grant.
The topic of river diversions has become more controversial in the last few years as fishermen and others question what large amounts of freshwater will do to fisheries stock.
A group of fishermen, some politicians and parish officials are pushing for smaller diversions but more marsh creation. The state has maintained that marsh creation is an important part of the restoration plan, but large river diversions are essential in certain areas as well.
Caffey and co-authors Hua Wang, of LSU, and Daniel Petrolia, of Mississippi State University, looked at the benefits and costs of each coastal restoration method and compared the dollar value of benefits if projects were at similar locations and size during the same time span.
The study appeared in the April issue of Ecological Economics as an examination of the economic trade-offs between a slower diversion-based approach and a more expensive but quicker dredge-based marsh creation approach.
The study concludes that the sooner the restoration happens the more economic benefits the project will provide. In some situations, the economic benefit of having immediately created land through marsh creation outweighs the additional cost of the technique compared to river diversions.
Conventional wisdom about diversions of freshwater and sediment from the Mississippi and Atchafalaya rivers is that it makes sense as a restoration tool because the river is what built large portions of south Louisiana in the first place.
However, the conventional wisdom of the economic efficiency of diversions is accurate only if a number of assumptions are made, Caffey said.
Those assumptions include:
- that diversion-benefit projections in the 2012 state coastal master plan are correct.
- that the estimated cost of sediment diversions is correct.
- that an acre of wetland in 50 years is worth the same as an acre restored today.
As the state continues designing a sediment diversion to be located in Myrtle Grove in Plaquemines Parish, officials should also look at a wider spectrum of cost and benefits over time.
“Diversions clearly have a place, but the front-loaded benefits of marsh creation shouldn’t be dismissed because it’s not natural,” Caffey said.
That’s not to say marsh creation has been ignored within the state’s 50-year, $50 billion plan for coastal restoration and protection. That plan calls for $20 billion estimated for marsh creation while $3.8 billion is estimated for the construction of sediment diversions.
However, that hasn’t stopped diversion proponents and opponents from trying either to vilify the report or to hold it up as a reason why diversions shouldn’t be built, Caffey said. The report doesn’t do either.
Jerome Zeringue, chairman of the Coastal Protection and Restoration Authority, said the diversions in the study are freshwater diversions, but that’s not the same as what a sediment diversion combined with sediment dredging could do over time.