. The ecology of delta marshes of coastal Louisiana : a community profile. Marsh ecology -- Louisiana; Wetlands -- Louisiana. These meteorologically driven water level changes are common events. Tropical storms are much more unusual . When they occur water levels can be dramatically elevated. The water level height/fre- quency curve for Shell Beach, southeast of New Orleans (Figure 12), shows that wind tides as high as m have been recorded, and tides occur about once every eight years. On a coast with a slope of about mm/km (Byrne et al. 1976) a tide can cause flooding hund
. The ecology of delta marshes of coastal Louisiana : a community profile. Marsh ecology -- Louisiana; Wetlands -- Louisiana. These meteorologically driven water level changes are common events. Tropical storms are much more unusual . When they occur water levels can be dramatically elevated. The water level height/fre- quency curve for Shell Beach, southeast of New Orleans (Figure 12), shows that wind tides as high as m have been recorded, and tides occur about once every eight years. On a coast with a slope of about mm/km (Byrne et al. 1976) a tide can cause flooding hundreds of kilometers inland. The ecological effects of such flooding can be dramatic. GEOLOGICAL PROCESSES The Mississippi River, the largest river systan in North America, drains an area of 3,344,560 km^ (Coleman 1976). The average discharge of the river at the delta apex is approximately 15,360 cimecs with a maximum and minimim of 57,900 and 2,830 cijmecs, respectively. Sediment discharge is generally about ^^ kg annually. The sediments brought down by the river to the delta consist primarily of clay, silt, and sand. The sediments are 70 percent cl ay. The river has had a pronounced influence on the development of the northern Gulf of Mexico throughout a long period of geologic time. In the Tertiary Period (70 - 1 million years before the present) the large volumes of sediment < UJ CO z O CD <. 100 50 OCCURRENCES/100 YEARS Figure 12. Tide levels at Shell Beach, in the Pontchartrain-Lake Borgne basin, associated with nine major storms (Wicker et al. 1982). brought down by the Mississippi River created a major sedimentary basin, and many of the subsurface deposits, especially those that formed in localized centers of deposition, have been prolific hydrocarbon-produci ng reservoi rs. In more recent geologic times, changing sea levels associated with the advance and retreat of inland glaciers during the Pleistocene Ice Ages have strongly influenced the sedimentary patte
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