Examination of Deltaic Processes of Mississippi River Outlets-Caernarvon Delta and Bohemia Spillway in Southeastern Louisiana

摘要

Deltaic processes of the Mississippi River Delta have been severely limited by artificial river levees, which prevent overbank flows during Spring floods. To counteract the effects of severing the connection between the river and the delta, focus has been placed on reconnecting the river to the delta by the creation of artificial outlets or diversions. The Caernarvon Freshwater Diversion and the Bohemia Spillway are two legacy diversions located on the east bank of the Mississippi River south of New Orleans. The Caernarvon Freshwater Diversion was designed to deliver up to 8000 cfs from the Mississippi River. The sediment load in the diverted water is carried into the Caernarvon Diversion outfall area known as the Big Mar Pond. Turbidity measurements were taken from December 2009 through 2012 and used to calculate the total suspended solids (sediment load) delivered to the receiving basin. In total, approximately 264,000 yd~3 of sediment was delivered to the receiving basin. Often, the diversion is not operated when sediment spikes are present and therefore does not maximize potential sediment capture. Despite this variability in operation of the diversion, and the fact that the Caernarvon Diversion was built to minimize sediment capture, there has been enough accumulation in some areas to permanently support emergent wetland plant life on a new sub-delta. Total wetland growth of the sub-delta in Big Mar Pond from 1998 to 2011 was 600 ac. Of this total, 581 ac were new growth since 2004. This pattern is similar to that documented for other larger diverted flows, such as the Wax Lake Delta, where there is an initial delay in wetland growth as mineral soil platforms vertically accrete to a threshold on which emergent vegetation can survive.