The dream that we can make enough freshwater diversions from the Mississippi into the Barataria Basin to the west and Breton Sound to the east to reverse land loss is a fantasy.
A pair of geologists at Louisiana State University issued a report last week, noting that we have deprived the Mississippi River of the sediment necessary to counter the raise in sea level and rebuild the Louisiana coast.
The researchers have concluded that the 8,000 dams we have built in the Mississippi Basin are the culprits. Any sediment that may flow out of the uplands into the tributaries gets trapped behind the dams.
We built the 26 dams on the Upper Mississippi to turn it into a profitable navigation channel. All the sediment that comes out of the uplands is trapped behind the dams. The Corps of Engineers must dredge the navigation channel constantly to maintain its 9-foot depth.
There are six on the Missouri, which flows through soft, erodible sedimentary rocks and supplied the Mississippi with 60% of its sediment before the construction of its dams in the 1950s.
Take the Niobrara River, which flows to the Missouri at Niobrara, Nebraska. It heads neat Lusk, Wyoming and flows along the northern margin of the soft, erodible Sand Hills in Nebraska, turns north, and empties into the Missouri.
It is a river that somehow has not been dammed or channelized, but it has still been changed by the construction of the Gavins Point Dam downstream from its confluence with the Missouri. The dam turned the Missouri into a lake and raised the level of the Missouri 2.9 meters at the mouth of the Niobrara.
Note: When a fast moving stream meets a still body of water, it deposits its sediment in the still body of water and forms a delta. That’s what the Niobrara does with the sediment eroded from the Sand Hills when it meets the lake-like Missouri. This is the case with other tributaries of the Missouri. It is all retained behind the Missouri River dams.
Before the construction of the dam, the Missouri carried away all that sediment to the Mississippi, which delivered it to a still body of water: the Gulf of Mexico and built the Louisiana coast.
Now what sediment the Mississippi does carry to the Louisiana Coast does not get to it because we have built levees clear to Venice, Louisiana to prevent the river from flooding and depositing its sediment on the coast. Hence, we have to design freshwater diversions to deliver sediment to the wetlands, which are starving for lack of freshwater and sediment. But, now we are finding those won’t work.
 Etheridge, F.G., Skelly, R.L., Bristow, C.S., “Avulsion and Crevassing in the sandy, braided Niobrara River complex response to base-belel rise and aggradation,” In Fluvial Sedimentology by Norman Dwight Smith and John Rogers, found in Google Books http://books.google.com/books?id=7i_pWcmzRZ4C&pg=PA181&lpg=PA181&dq=Niobrara+Missouri+River&source=bl&ots=94teq3rvPZ&sig=_Ua9y4paapkbENbXSDPBU6r6rhQ&hl=en&ei=pS5KSoq_K4f-NZ-c-fIN&sa=X&oi=book_result&ct=result&resnum=6.