PANEL DISCUSSION 



CAUSES: CHANGES IN DISPERSAL OF FRESH WATER AND SEDIMENTS 



Gerald G. Bordelon, Moderator 



Johannes van Beek, Richard Hatton, Ron Boyd, John Wells, 

 Clark Lozes, and Raphael Kazmann, Panelists 



Gerald Bordelon: The presentations ranged from a doomsday to a new birth, starting out 

 with a snorl<el and little worry to some good hope. 



David Soileau: There has been concern about the potential adverse impacts of the 

 proposed Avoca Island levee extention on the marshes to the east, but the Corps of 

 Engineers has pointed out the potential beneficial impact on the tupelo-cypress and 

 bottomland hardwood areas to the north of the marshes. Dr. van Beek, what is your 

 opinion on this from a hydrological viewpoint? 



Johannes van Beek: The hydrological issue is whether the Avoca Island levee extension 

 will reduce water levels in the areas north of Morgan City and in the Verret Basin. 

 The answer is yes it will, initially, in so far as those water levels are controlled by 

 the stage of the Atchafalaya River as felt at the Amelia Channel. This will only be 

 a temporary effect, however, because of the effects of other processes, namely 

 subsidence and increase in stages in the Atchafalaya River due to channel 

 development and delta progradation. Flooding in the basin east of the Atchafalaya 

 Basin is not due to backwater flooding alone, but due to backwater flooding 

 superimposed on tides, increased water levels due to onshore winds and large 

 rainfalls in the basin accelerated by channelization for the purpose of agricultural 

 drainage. 



Joel Lindsey: Ring levees around developed areas have been proposed as an alternative 

 to the Avoca Island levee extension. Which would be the most cost-effective means 

 of flood protection? 



Johannes van Beek: That is difficult to answer because of the term "cost-effective." 

 While we do not yet have all the answers, we have learned quite a lot about deltaic 

 processes and have documented changes. We have at least the nominal 

 understanding necessary to suggest future directions. This involves planning for land 

 use on a statewide basis and a commitment to those plans. It means if we have to 

 relocate people, we will do it. Eventually we will be forced to that anyway, because 

 we cannot stop what is happening along the Louisiana coast. We can buy time, but 

 we cannot stop delta cycles. We can initiate new ones, but this too requires human 

 adjustment. 



David Mekasski: What would be the effect of opening the Bonnet Carre spillway on a 

 regular basis to marsh and shoreline accretion in western Lake Pontchartrain? 



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