DEMONSTRATION PROJECT 

 STUDY AREA 



Approximate Scale 

 Kilometers 



^^"■^^ 



Figure 7-1 : Selected stations used for analysis of long-tetTn salinity changes in Rincon Bayou. 



be termed a "reverse estuary," because the gradient was 

 opposite what would be expected from a natural 

 (undisturbed) system in which salinity concentrations 

 would be lowest in the upper delta {e.g., at Station 66). 

 For the period after the demonstration project, the 

 salinity gradient reverted to a more natural pattern for 

 much of it's reach, particularly within the upper and 

 middle Rincon Bayou segments (or the first 5 km from 

 the IH 37 bridge) (Figure 7-2b). This change was due 

 to increased diversions of fresh water through the 

 demonstration project features. Without the 

 demonstration project, average salinity concentrations 

 in upper Rincon channel during the second period 

 would have remained strongly hypersaline (likely 

 greater than 50 parts per thousand (ppt) instead of the 

 observed range of 21 to 28 ppt. 



As expected, the demonstration project had no obvious 

 effect on the salinity pattern of the Nueces River, nor 

 was it designed to (the project was found to only divert 

 approximately 2% of total river flow during a given 



hydrographic event (Ward 2000)). During both 

 periods, salinity concentrations in the river channel 

 increased with distance downstream as riverine fresh 

 water (e.g., at Station 68) mixed with salt water from 

 Nueces Bay (e.g., at Station 7) (Figure 7-2). 



From comparison of the actual average salinity values 

 in the river and bayou between both periods (i.e.. 

 Figures 7-2a and 7-2b), it is apparent that salinity 

 concentrations were generally higher during the after- 

 project period than before the project. For example, in 

 the Nueces River, this difference was about 3 parts- 

 per-thousand (ppt) in the middle of the river 

 (Station 4b) and about 8 ppt in the open bay 

 (Station 7). This observation does not indicate that the 

 demonstration project increased average salinity 

 concentrations in the river but more likely is 

 attributable to a greater freshwater influences on the 

 river from both river flow and precipitation during the 

 period before the project than after (Figure 7-3). 



Chapter Seven ^ 7-3 



