Table 5. Water exchange indices and average white shrimp production estimates for each study 

 site. 



Site 



Cross-sectional 

 area of water 



control structure 

 Water at the most 

 area constricted point 8 

 (ha) (m 2 ) 



Water 

 exchange 

 index^ 

 (m 2 :ha) 



Average 

 white shrimp 

 production 



Elevation and 

 description of water 

 control structure 



Non-weired 

 Grand Bayou 



26.5 



2.78 



1:9.5 



28.7 



Base of structure 

 152 cm below marsh 

 level. 12.2-m-long, 

 183-cm-wide wooden 

 chute. 



Low-level weir 

 Grand Bayou 



26.5 



0.5 



1:53.0 



8.1 



Weir crest set 30 cm 

 below marsh level, 

 165 cm long. Weir 

 located in a wooden 

 chute same as above. 



Little Pecan 

 Lake 



174 



1.17 



1:148.7 



14.3 



Base of structure 

 127 cm below marsh 

 level 9.1 -cm-long, 122- 

 cm-diameter corrugated 

 aluminum culvert with 

 flap-gate and stop-log 

 bay (weir crest length 

 231 cm). 



8 Cross-sectional area below marsh level. 

 b Calculated using data from the first two columns. 

 c Data taken from Table 3. 



to that for a fixed-crest weir semi-impoundment (Rogers et al. 1987). Water exchange at the 

 fixed-crest weir site was affected differently compared to the other sites where exchange occurred 

 through a 122- to 162-cm-deep water column. Therefore, water exchange at the fixed-crest weir 

 site cannot be accurately compared with that from either of the other sites. 



The 162-cm-deep unobstructed wooden chute at Grand Bayou and the 122-cm-diameter culvert 

 at Little Pecan Lake were relatively similar in regard to the mechanism by which they reduced 

 water exchange. For these sites, exchange indices may be used to compare the extent to which 

 water exchange was reduced. 



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