of the chenier plain relative to the cycle of land building and land loss? (2) What 

 connection exists between the developing Atchafalaya River delta and chenier plain 

 sedimentaion? and, (3) What is the future for the land building in Louisiana's western 

 coastal parishes? 



PRESENT STATUS 



Development of the chenier plain according to the broad brush model presented 

 above might be expected to produce a modern shoreline either uniform in character or at 

 least gradational from east to west. In fact, the coastline from Marsh Island to the 

 Texas border shows as much variability as any in Louisiana. Kaczorowski and Gernant 

 (1980) have recognized three distinct types of modern shorelines to which we add a 

 fourth. The Type I shoreline is one of perched beaches with exhumed marsh cropping out 

 in the surf zone (Figure 2A). Beaches consist of shell hash and sand in variable 

 proportions, typically fronted by a storm berm less than 0.75 m in elevation and backed 

 by washover deposits extending not more than 100 m into a brackish marsh back-barrier 

 environment. This type of shoreline fronts more than one-half of the chenier plain coast. 



The Type II shoreline is one of unvegetated mudflats and can be divided into two 

 subcategories on the basis of sand content and origin. The first contains less than 5% 

 sand and shell and is composed of a fluid mud derived from an offshore source (Figure 

 2B). These mudflats are not permanent features and today appear to be localized in a 

 20-km stretch of coast extending from the mouth of Freshwater Bayou Canal west to 

 Rollover Bayou. The second type of "mudflat" may contain greater than 30% sand and 

 shell and is found updrift (east) of the jetties at Calcasieu and Sabine passes. These 

 essentially artificial accumulations reflect an interception of locally derived and 

 reworked sediments. 



The Type III shoreline is a sand/shell beach which differs from the Type I in that it 

 represents a reactivated relict deposit (Figure 2C). Such deposits are found at intervals 

 along the modern coast wherever the present surf zone truncates or parallels a chenier 

 ridge. These beaches are most common in the western part of the chenier plain where 

 the spacing between ridges is closer. Coarse material eroded from deposits up to 3,000 

 years old is entrained in the modern longshore drift system and nourishes Type I beaches 

 to the west. Type III beaches exhibit a large range in morphology, show up to 4 m of 

 relief, and may contain relict dune fields such as that at Chenier au Tigre on the eastern 

 margin of the Chenier Plain. 



The Type IV shoreline is one in which no continous beach exists. Brackish marsh 

 headlands extend into the gulf at intervals of 20 to 50 m and shelter crescentic pocket 

 beaches which contain minor accumulations of shell hash and organic debris (Figure 2D). 

 With the exception of the Type II mudflats, all of these shorelines are erosional and have 

 historically retreated between 3 and 10 m/yr (Adams et al. 1978). Relatively stable 

 sections are located at Chenier au Tigre in the east and between Calcasieu and Sabine 

 passes in the west. 



Areas of Type II mudflat accumulation along the coast of the eastern chenier plain 

 were determined from color infrared photographs taken in October 1974 and October 

 1978 (NASA Missions 74-293 and 78-148, respectively), from 1974 orthophotoquads, and 

 from aerial and ground reconnaissance in 1974, 1979, and 1981. Results of these photo 

 and ground comparisons, together with assessments by Adams et al. (1978) for 1954-69 

 are shown in Figure 3. 



42 



