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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 45 (1995), Pages 113-122

Historical Shoreline Dynamics Along the Chenier Plain of Southwestern Louisiana

Mark R. Byrnes, Randolph A. McBride, Qiang Tao, Lisa Duvic

ABSTRACT

A computer-based shoreline mapping methodology, within a framework of a geographic information system, was used to compile and analyze changes in historical shoreline position between Sabine and Southwest Passes in southwestern Louisiana for the period 1883 to 1994. Regional patterns of change depict systematic shifts between shore retreat and advance in relation to sediment supply from the westward-directed Atchafalaya River mudstream and erosion of marsh/chenier deposits, as well as shoreline orientation relative to storm and normal wave conditions. Net shoreline position change for the period 1883 to 1994 illustrates seven cells of accretion and erosion and one cell showing no net change. The western 17 km of coast (5 km east of Sabine Pass to west Ocean View Beach) illustrates net advance of 3.5 m/yr. Moving east, the next 15 km of coast (Ocean View Beach to the eastern end of the revetment along Highway 82) shows net retreat at 1.2 m/yr. A 2-km segment of coast bracketing Holly Beach shows no net change, but an 8.5-km length of coast east of this area has been retreating at a rate of 1.4 m/yr since 1883. Shoreline change from 0.7 km west of the Calcasieu Pass jetties east to the old Mermentau River mouth has averaged +2.7 m/yr; however, the 63-km segment of coast east of this area shows net retreat at a rate of 8.7 m/yr. From western Mulberry Island to Cheniere au Tigre, shoreline advance has been dominant at 2.8 m/yr, whereas east of this zone to Southwest Pass average shore erosion at 2.9 m/yr is illustrated. Although shoreline retreat is dominant over much of the chenier plain (average change rate for the period of record is -2.6 m/yr), long-term trends indicate net shoreline advance between Sabine and Calcasieu Passes (0.7 m/yr) and average shoreline retreat between Calcasieu and Southwest Passes (3.8 m/yr) since 1883.


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