transport divergence from the central erosional headland and sediment accumulation 

 downdrift of flanking barrier islands and tidal inlets both east and west of the erosional 

 headland. The Caminada-Moreau coast is a low barrier beach, approximately I m above 

 msl. This beach is a thin, continuous washover sheet with Holocene marsh outcropping on 

 the lower beach face, reflecting a negative sediment budget and rapid coastal erosion. 

 Increasing downdrift sediment abundance leads to the development of small channels, 

 washover fans, and low, hummocky dune fields which eventually coalesce further 

 downdrift to forma higher, more continuous offshore terrace, and eventually, a foredune 

 ridge (Figure I I). Downdrift flanking barrier islands migrate laterally, in the direction of 

 longshore sediment transport, by erosion at the updrift ends and accretion downdrift. 

 Washover sheets and multiple shallow breaches are common on the updrift or erosional 

 ends of these islands. Downdrift, longshore bars become more prominently developed in 

 the nearshore zone, and toward the eastern end of the system bars become attached. In 

 these downdrift zones, active beach ridge progradation is taking place. Recurved spit 

 morphology formed during the growth of Timbalier Island and Grande Isle indicates the 

 importance of an updrift sand source in the Caminada-Moreau erosional headland (Figure 

 12). 



Shoreline Changes 



In the erosional headland/flanking barrier stage, the greatest shoreline erosion 

 problems are within the erosional headland itself and on the updrift ends of the flanking 

 barrier islands (Figure 10). Along the Caminada-Moreau coast, erosion rates are 10 to 20 

 m/yr. Figure 13 shows the pattern of shoreline change from the Late Lafourche barrier 

 system between 1887 and 1978. Note the rapid shoreline retreat of the 

 Caminada-Moreau coast. Shoreline erosion and coastal spit progradation have smoothed 

 the earlier irregular shoreline of 1887 and closed all of the distributaries except Belle 

 Pass. The severest erosion is in the vicinity of Bays Marchand and Champagne. The 

 Orthogonal Grid Mapping System (OGMS) data from 1934-78 shows that this erosion 

 pattern is continuing. At Bay Champagne, the greatest rate of shoreline retreat 

 measured for the 44-year period was 22.3 m/yr, with erosion decreasing eastward to 9.6 

 m/yr at Bayou Moreau. Field measurements along the Caminada-Moreau coast made in 

 1979 by the Louisiana Barrier Island Project show that tropical cyclones accounted for 

 over 70% of the total annual erosion in that year (Figure 14). 



In the Belle Pass area, erosion rates average 18.6 m/yr prior to 1954; after 1954, 

 the OGMS data show shoreline erosion slowing, switching to accretion sometime after 

 1969. The sedimentation pattern changed in response to jetty construction at Belle 

 Pass. Jetties 152 m long and 61 m wide were constructed at Belle Pass in 1934 to 

 improve the navigation channel at Bayou Lafourche. In 1968, the jetties were expanded 

 to 218 m long and 140 m wide, and the Bayou Lafourche navigation channel was dredged 

 to a depth of 6 m, width of 90 m, and extended 2 km offshore (Dantin et al. 1978). These 

 improvements created a formidable barrier to longshore sand transport and sediment 

 bypassing to the west around Belle Pass to the Timbalier Islands. The first jetty system 

 appears to have had little effect on the local sediment-dispersal pattern. The shoreline 

 continued to erode at rates averaging 18 m/yr, with no significant sand accumulation 

 updrift of the jetty system. In fact, the jetty system had to be extended landward 

 several times to keep pace with the retreating shoreline. It was after the 1968 

 improvements that the sedimentation began taking place along the eastern side of Belle 

 Pass. Accretion rates there have averaged 5.5 m/yr since 1969, representing a sink for 

 material that would otherwise be transported further west to the Timbalier Islands. 



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