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The Gulf Intracoastal Waterway as a Distributary of Mississippi River Water to Coastal Louisiana Wetlands

East-west trending ship channel, 12-20 ft deep, at least 200 feet wide; in study area built mid-1930's Parallels upland/wetland interface near upland boundary; crosses marshes and swampsCrosses south flowing Lower Atchafalaya River and Wax Lake Outlet in south-central Louisiana. Map of GIWW in coastal Louisiana.

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The Gulf Intracoastal Waterway as a Distributary of Mississippi River Water to Coastal Louisiana Wetlands

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    1. The Gulf Intracoastal Waterway as a Distributary of Mississippi River Water to Coastal Louisiana Wetlands Christopher M. Swarzenski US Geological Survey Baton Rouge

    2. East-west trending ship channel, 12-20 ft deep, at least 200 feet wide; in study area built mid-1930’s Parallels upland/wetland interface near upland boundary; crosses marshes and swamps Crosses south flowing Lower Atchafalaya River and Wax Lake Outlet in south-central Louisiana

    3. Map of GIWW in coastal Louisiana

    9. Comparison of GIWW discharge with that of controlled river diversions (average Jan-Jun) GIWW Across Jaws 8,040 cfs At Bay Wallace 9,440 cfs East of B. Lafourche 1,750 cfs Controlled River Diversion Caernarvon 2,100 cfs Davis Pond 2,340 cfs

    12. Long-term salinity patterns at Sister Lake

    13. Conclusions THE GIWW CAPTURES WATER FROM THE NORTH SOUTH FLOWING LOWER ATCHAFALAYA RIVER (ITSELF MAINLY MISSISSIPPI RIVER WATER) PASSIVLEY AND ROUTES IT TO POINTS EAST AND WEST 50 OR MORE MILES DISTANT THE GIWW IS INTRODUCING MORE RIVER WATER AND SUSPENDED SEDIMENTS TO DELTA PLAIN MARSHES THAN THE LARGEST MAN-BUILT CONTROLLED RIVER DIVERSIONS THE FRESHWATER IN THE GIWW INFLUENCES SALINITY IN MANY PARTS OF THE COAST, DEPENDING ON TIMING OF SPRING PULSE AND SEASONAL SEA LEVEL VARIATIONS AN IMPORTANT ATTRIBUTE OF THE GIWW FLOW IS MAINTAINING HEAD DIFFERENCES WITH COASTAL SURFACE WATERS, IMPEDING SALT WATER ENCROACHMENT

    14. THE THEORY IS THAT RIVER WATER INFLOW WILL REBUILD OR PERHAPS SUSTAIN THE DETERIORATING MARSH LANDSCAPE THE REALITY PROBABLY IS A BIT MORE COMPLICATED WHAT ABOUT WETLAND BUILDING ?

    15. WHAT ABOUT WETLAND BUILDING ?

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