area of the wetlands. According to Zack (1973). max- 

 imum seepage occurs when surface water levels are 

 highest, i.e., during the spring, and late summer to 

 early fall. Less important recharge sources are 

 through fractures associated with faulting from salt 

 domes, and inter-aquifer exchange in localized areas 

 where separating clay layers become thin or non- 

 existent. 



The most important ground-water aquifer in the 

 Chenier Plain is the Chicot Aquifer, which was formed 

 during the Pleistocene age. I'his aquiter supplies more 

 than 90% of all ground water pumped in the Chenier 

 Plain (Guevara-Sanchez 1974). in the hydraulic center 

 of this aquifer, Calcasieu Parish and vicinity, extensive 

 clays separate the Chicot Aquifer into three distinct 

 layers: 60 m (197 ft), 150 m (492 ft), 210 m (689 ft) 

 sands. Massive beds of sand and gravel ranging from 

 15 to 250 m (49 to 820 ft) in total thickness are over- 

 lain by extensive, impermeable clay beds. Alternating, 

 interfingering lenses of sand and mud are found in the 

 shallow subsurface of southeastern Texas. The verti- 

 cal and lateral distribution of sand in this region 

 suggests that the Chicot Aquifer may comprise several 

 local aquifers separated by mud intervals that are 

 locally well-developed (Guevara-Sanchez 1974). The 

 deposits slope gently gulfward 1 to 3 m/km (2 to 6 ft/ 

 mi) and increase in thickness from less than 30 m 

 (98 ft) in northern Louisiana to more than 2,150 m 

 (7,054 ft) beneath the Gulf of Mexico. Thickness 

 increases from Lake Calcasieu east to Wliite Lake and 

 then decreases to the Atchafalaya Basin. To the west 

 the beds become thinner, although localized vari- 

 ability is much greater than to the east of Lake Cal- 



casieu. Aquifers of the Chicot reservoir have been 

 tapped by offshore wells and contain freshwater 

 beneath the Gulf of Mexico near the shoreline be- 

 tween Cameron and the Atchafalaya river. 



Older Miocene and Phocene aquifers, although 

 large, are used only indirectly. The Pliocene aquifers 

 are directly connected to the Chicot reservoir in many 

 areas; therefore, an indirect withdrawal is taking 

 place. Due to the numerous interconnections in south- 

 east Texas, the PHocene and Pleistocene aquifers are 

 collectively known as the Gulf Coast Aquifer. 



2.5.1 USAGE OF GROUND WATER 



Cyclical, and continuous ground-water pumping 

 takes place in the Chenier Plain. Irrigation require- 

 ments are cychcal (spring and summer): municipal 

 and industrial needs are continuous. Ground-water 

 withdrawal volumes by activity are presented in parts 

 3.2.3 and 3.2.6. In the Chenier Plain and immediate 

 vicinity the total withdrawal is 2 x lO'm^ (7.06 x 

 lO^'ft ) per yr, with irrigation accounting for 74% 

 of the usage, industry 17%, and municipalities and 

 rural areas 9% (Louisiana Department Pubhc Works 

 1971, Baker and Wall 1976). Pumping has been in- 

 creasing annually: in the Lake Charles area the rate 

 of increase is about 2.8 x lO^m^ (9.89 x 10''ft^) per 

 yr (Harder et al. 1967, fig. 2-8). Based on the esti- 

 mated freshwater recharge rate for aquifers currently 

 being pumped in southwestern Louisiana (Jones et al. 

 1956) and extending this rate to the Texas area of re- 

 charge, use exceeds recharge by 1 x lO'm^ (3.53 x 

 10''ft^)peryr. 



160 



120_ 





o 



c 

 e 



80_ 



40_ 



O U- 



. -.^'700»oot" Sand 

 ..1210ml 

 :V 2 00 foo t" Sand 160 ml 



•^ *- 



It 



\ 



40 



45 



50 



55 



Year 



60 



65 



70 



75 



T 



% 



Figure 2-8. Volume of water pumped from different sand strata in the Lake Charies area from 1935-65 (Harder 

 etal. 1967). 



22 



