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-50 



-60 



-70 



-80 



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-100 



10000 20000 30000 40000 50000 60000 70000 80000 90000 100000 



Total event flow volume in the Nueces River (acre-ft) 



Figure 5: Fractional salinity response versus flow volume in Nueces River (measured at Calallen). 



Note: 1 acre-tt= 1.2336x10' I 



Nueces River was observed within the scatter of the data. That water diverted through the overflow channel 

 would not measurably affect the response of bay saUnity was not surprising, given the very small proportion of 

 flow volume diverted through the overflow channel compared with that in the river. 



Second, the rate of decrease of the fractional response (that is, the increase of negative values) with increasing 

 flow in the Nueces River appeared to asymptotically trend to -100%. Considering that the mean water level 

 volume of Nueces Bay is about 49,344 10' m' (40,000 acre-ft) (Ward 1997), one might have expected the 

 fractional responses to equal -100 percent for flow volumes exceeding this 12,336 10' m'. But this was not the 

 case, probably because the definition of an "event" may encompass some of the period of salimty recovery. 

 Moreover, there were also hydrographic processes that enabled water from lower in the bay (and containing 

 higher salinity) to infiltrate back into Nueces Bay during the event period, including tides and wind forcing. 

 Finally, the adjective effect of the Nueces River depended not only upon its volume, but also the period over 

 which this volume is delivered. 



Finally, for total event flow volumes in the Nueces River of less than 12,336 10' m' (10,000 acre-ft), the 

 fractional salinity response became extremely noisy, and even became positive for a significant number of the 

 events. Restating this observation in another way, below a threshold volume in the river, other non- 

 hydrological factors become equally or more important in affecting the salinity of Nueces Bay, and the apparent 

 value of this threshold is around 12,336 10' m'. Similar threshold-type controls on salinity were theoretically 

 expected and have been found to operate when salinity and flow data are adequate to characterize the response, 

 such as in Trinity Bay in the Galveston system. Although quantification of this threshold was not relevant to 

 evaluating the effects of the subject demonstration project, it may be important in devising operating strategies 

 for future such diversions. 



Appendix B ♦ B-11 



