Potential for Restored Freshwater Inflow into the Upper Nueces Delta 



One way of assessing the potential for how the Rincon Bayou Demonstration Project might restore freshwater 

 flows to the upper Nueces Delta is to assiime that it had been in place in the past, and compare the results with 

 what actually occurred. Event magmtude, duration, frequency' and timing were therefore analyzed assuming that 

 the demonstration project features had been in place since the completion of Choke Canyon Reservoir 

 (Period III), which was generally assumed to represent realistic future conditions. The results from this 

 "restored" condition, when compared to those of the historical condition, would then give an indication of the 

 restorative potential of the project. 



Magmtude 



The restored event magnitude for Period III, when compared with average monthly volumes that historically 

 flowed into the upper Nueces Delta during Periods I and II, was almost imperceptible (Figure 15). The largest 

 average monthly discharge amount (May) was only 1,208 10' m' (980 acre-ft), which represented only a fraction 

 of the average for the same month during Periods I or II (2.5% and 16.8%, respectively). 



However, in the limited context of present 

 conditions {i.e.. Period III only), the restored 

 event magnitude compared much more 

 favorably, increasing the estimated average 

 monthly discharge by several rimes over 

 what had occurred without the 

 demonstration project. When analyzed 

 annually, the restored event magnitude 

 increased by over 633% from the historical 

 Period III amount (Table 6). 



Duration 



Table 6: Summary of restored annual event magnitude In the 

 upper Nueces Delta. Mean discharge value rounded to the nearest 

 10 acre-ft. 



Period 



1982-1999 



Restored 



Mean Total Discharge 



per Year 



(acre-ft) 



Percent Change 



from Historic 



Period III 



Conditions 



3,420 



633% 



Note: 1 acre-ft = 1 2335 10^ m' 



Restored event duration, xmlike restored magnitude, compared very favorably with the historical duration of 

 events flowing into the upper Nueces Delta (Figure 16). Both seasonal peaks were strongly evident, and the 

 spring peak (May) was approximately the same duration as that of the Period I. The restored event duration 

 even slightly exceeded the historical duration of both Periods I and II for seven (7) of the twelve (12) months of 

 the average year, and in only two months was it lower than the historical Period II values. The only notable 

 limitation of the restored event duration was that of the fall peak, which only attained an average of 2.5 days 

 (October), compared to the historical fall peak of 4.8 days (September) in Period I and 4.2 days (October) in 

 Period II. 



From the perspective of present conditions 

 (Period III) only, the restored event 

 duration also greatly surpassed historic 

 levels (Table 7). The restored annual event 

 duration increased by over 578% from that 

 historical (without-project) level to 

 26.0 days. 



Table 7: Summary of restored annual event duration in the upper 

 Nueces Delta. 



Period 



1982-1999 



Restored 



Mean Number of Event 



Days per Year 



Percent Change 



from Historic 



Period III 



Conditions 



26.0 



578% 



Note: 1 acre-ft = 1 2335 10^ m^ 



C- 1 8 ^ Analysis of the Historic Flom Re^me of the Nueces River into the Upper Nueces Delta 



