Thereafter, weir management will be a combination of science, accepted methods, and trial and 

 error. 



WATER LEVELS AND FLOW 



Water levels at the 5-ppt isohaline line are to be maintained at levels ranging from 15 cm below 

 marsh elevation to 6 cm above marsh elevation. Water level and tide data have been collected in 

 Grand Bayou for several years, and this data collection will continue in Grand Bayou and in marsh 

 soils at the evapotranspiration data collection site. These data will supply water-level information 

 before and after weir placement and provide information needed to manage water levels and flow. 



Temporary closures of the boat bay and other bays will be allowed if salinities exceed 5 ppt. 

 The effects of weirs on flow direction and volume in this system are unknown at this time. 

 Estimated decreases in vertical plane area at Grand Bayou and Lamberts Bayou will be 88.2% and 

 91.0%, respectively. After the first year, waterflow may be managed to facilitate a viable drawdown 

 from the eastern reaches of the marsh and allow ingress from the west, because waters flowing into 

 the system should be at lower volumes and channels leading to the east will start to fill with 

 sediment. 



SALINITY 



Isohaline lines of 12 and 5 ppt were determined using Chabreck's (1972) vegetative survey. 

 Salinity data has been collected since 1966 for six stations within the Grand Bayou waterway (ECl- 

 EC6). In October 1987, four more stations were established in Grand Bayou to determine 

 saltwater movement further east into the marsh (EC7-EC10). Eleven stations were established 

 along Highway 27 (H27 1-278) to determine saltwater movement to the eastern fringe of the East 

 Cove marsh. Salinity stations were also established at each weir site and 0.4-0.8 km inland from 

 each site to determine directional saltwater flow into the system. Data is collected every 2 weeks 

 with a Yellow-Springs Instrument Co. model 33 salinity meter. 



Long term salinity averages from EC1, EC6, and EC5 indicate a decrease in salinities from the 

 mouth of Grand Bayou to the headwaters of East Prong (Table 1). However, there are 2 periods 

 when salinities are higher at EC5 than EC6. These are April through May and September through 

 November. It is assumed that the seasonal decrease in precipitation, increase in Calcasieu Lake 

 salinities, and continuing evapotranspiration are causes of increased open water salinities further 

 inland. Recent data from EC7, EC9, and H277 indicate this trend; yet, it is not known if this data 

 is representative of the long term average (Table 2). Data from Station H277 indicate it is a 

 brackish water system until February. Station H277 is the furthest point northeast into the 

 watershed. 



Based on plant salinity tolerance data (SCS 1977), long term monthly salinity averages are at 

 stress levels for many historic and presently surviving plants (Table 3). Many of the plants once 

 common to this marsh have disappeared with increased levels of water salinities, according to 

 Berton Daigle, a life-long native of this area (pers. comm.). Three factors to consider when 

 comparing these data and observations are (1) salinity data are averages and not the maximum 

 salinities which have occurred, (2) salinity data are open-water salinities, not marsh-soil salinities 

 that may maintain a higher salt content, and (3) average plant salinity tolerance data used here 

 have rather large standard deviations and may reflect the variable water regime at the time of 

 sampling plant stress levels. 



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