Mississippi River Delta Subsidence Caused by Compaction

On February 17, 2008, Torbjorn E. Tornqvist of Tulane University and other researchers published a letter in the journal Nature Geoscience entitled Mississippi Delta subsidence primarily caused by compaction of Holocene strata. The research findings suggest that the Mississippi delta is sinking as much as one fifth of an inch per year, but that the sinking is mostly limited to the upper layers of sediment while the land beneath is more stable.

This research suggests that the high rate of subsidence is largely the result of compaction of the shallow sediment deposits from the last 10,000 years in the upper few hundred feet near the surface of the earth. These findings suggest that flood control structures that penetrate through the shallow sediment deposits and rest on the more stable foundation below would not subsidence as quickly.

News articles reporting on this research include: Science Daily in an article entitled Post-Katrina Rebuilding? Mississippi Delta Both Spongy and Stable published on February 22, 2008; and New York Times in an article in a section entitled Observatory with the article title Support for a Theory As to Why Land Sinks Along the Gulf Coast by Henry Fountain published on February 19, 2008.

Erich P Rapp

Corps Seeks Reimbursement for Mississippi River Dredging from Coastal Restoration Budget

Although efforts to stem coastal wetland loss in Louisiana are already grossly underfunded, the Corps of Engineers is seeking reimbursement for a part of the cost of dredging the Mississippi River to maintain the navigation channel from the budget for coastal restoration projects authorized and funded pursuant to the Breaux Act. See the editorial in the New Orleans Time Picayune on Monday February 18, 2008 and the related article in the New Orleans Times Picayune on Thursday February 14, 2008.

The Mississippi River Commission, which is related to and controlled by the Corps of Engineers, is taking the position that the State of Louisiana and the Corps of Engineers must pay for any increase in dredging costs that result from any coastal restoration project in Louisiana that diverts water and sediment from the Mississippi River.

Officials for the State of Louisiana believe that the transfer of this cost to the Breaux Act coastal restoration projects will effectively shut down the restoration projects.

Interestingly, Garret Graves, the Chairman of the Louisiana Coastal Protection and Restoration Authority and member of the Breaux Act task force suggested that perhaps the Corps should be responsible for the damage to the Louisiana coastal wetlands that resulted from the Corps management of the Mississippi River.

Melanie Goodman, the Corps' Breaux Act program manager replied that actions related to navigation "a century ago" which are damaging the coastal wetlands in Louisiana are in the past and not subject to reimbursement.

Of course, this entire blog is dedicated to the idea that the Corps is making decisions and undertaking actions everyday that adversely impact the Louisiana coastal wetlands and that the continuing series of interconnected decisions dating back many years is, in fact the responsibility of the Corps of Engineers and the federal government.

The Corps' two part defense is that it did not know they were damaging the coastal wetlands of Louisiana many years ago when they built dams and levees on the Mississippi River and its tributaries. This is, of course, not true. The Corps has known since the 19th century that the coast of Louisiana was subsiding and that the sediment from the Mississippi River offset the subsidence.

The additional implication from the Corps' claim about the past is that the Corps is not taking new actions today that adversely impact on the coast of Louisiana. This is also not true. The Corps makes management decisions about the Mississippi River and its tributaries such as the Missouri River and the Ohio River, everyday that deny or reduce sediment transport to the coast of Louisiana. In many ways, an analytical disconnect exists between management of the more northern portions of the Mississippi River drainage basin and the coast of Louisiana. The analysis of Corps projects in the Missouri River or the upper Mississippi River or the Ohio River almost never consider the impact of these projects on sediment transport to the coast of Louisiana, and those decisions and actions continue day after day and year after year up to the present and likely far into the future. The Corps' suggestion that the damage they have caused to Louisiana's coast is the result of actions far in the past is simply not true. It is also the result of events planned and executed in the present.

Erich P. Rapp.

Governor Issues Executive Order on Coastal Restoration Coordination

On January 23, 2008, Governor Bobby Jindal signed an executive order requiring all state agencies to comply with the Comprehensive Master Plan for a Sustainable Coast. This plan describes the coastal and hurricane protection priorities recognized by the Coastal Protection and Restoration Authority of Louisiana which Authority includes the Louisiana Department of Transportation and Development, Louisiana Department of Natural Resources and the Governor's Office of Coastal Activities. The executive order requires all state agencies to adhere to the projects and priorities listed in the state's master plan for coastal protection and restoration. 

Erich P Rapp.

Why Moving Water Transports Sediment and Also Cleans Clothes

When I have questions about basic geology, I refer to Physical Geology by Charles C. Plummer, David McGeary, and Diane H. Carlson. It is an introductory college text with great explanations for everything geology related with many pictures and diagrams. 

For example, why does flowing water transport or carry sediment? The answer is on page 28,

"In a water molecule, the two hydrogen atoms are tightly bonded to the oxygen atom. However, the shape of the molecule is asymmetrical, with the two hydrogen atoms on the same side of the atom. This means the atom is polarized, with a slight excessive positive charge at the hydrogen side of the molecule and a slight excessive negative charge at the opposite side. Because of the slight electrical attraction of water molecules, other substances are readily attached to the molecules and dissolved or carried away by water. Water has been called the universal solvent. Dirt washes out of clothing; water, in blood, carries nutrients to our muscles and transports waste to our kidneys and out of our bodies."

Of course for our purposes in this blog, streams and rivers also transport sediment.

Erich P Rapp.