The second study was conducted by Irlbeck and Ward 

 (2000), who used river over-banking events into the 

 upper Nueces Delta (i.e., Rincon Bayou) to generally 

 represent delta inflow. After analyzing the flow regime 

 characteristics of deltaic inundation events, it was 

 concluded that the magnitude of such events has also 

 decreased during the period of 1940 to 1999. Again, in 

 the context of reservoir construction, it was reported 

 that change in the annual mean flow into the delta 

 from the river during the period after the construction 

 of Lake Corpus Christi (1958 to 1982) was large (a 

 decrease of about 39%), and that the change during the 

 period after construction of Choke Canyon Dam (1982 

 to 1999) was very dramatic (a decrease of over 99%) 

 (Irlbeck and Ward 2000). 



The comparative results of these two investigations 

 (Table 2-1) show a marked difference in the response 

 of the Nueces Delta to reductiotis in stream flow over 

 the past sixty years when compared to that of the other 

 two periods (1958 through 1981, and 1982 through 

 1999) (Figure 2-16). The distribution of large 

 precipitation events were also found to be less frequent 

 during the drought years of the late 1940's and early 

 1950's than in the latter two periods, which were not 

 significandy different from each other (Medina 2000). 



This information is relevant because this first period, 

 which was used as the baseline for calculating percent 

 changes in estuary and delta inflow by Asquith et al. 

 (1997) and Irlbeck and Ward (2000), respectively, likely 

 under-represents to some degree the actual baseline 

 conditions for freshwater inflow to the Nueces Estuary 

 and Delta. In addition, the second period, which 



1940-1957 1958-1981 1982-1999 



H Sablnal H Beeville 5 NE 



n Corpus Christi CD Cotulla 



Figure 2-16: Mean annual precipitation of available 

 data at four gauges about the greater Nueces River 

 watershed. Source: Medina 2000. 



Note: 1 inch = 2.54 cm 



showed the smallest percent change in both analyses, 

 also experienced the largest mean watershed 

 precipitation (Figure 2-16). 



Changes in Ecology 



The history of the Nueces Estuary is not dissimilar 

 from that of many other estuaries, in that it includes 

 man-made alterations such as diverting or removing 

 freshwater sources, creating channels, extracting 

 sediments, disposal site of waste materials and 

 harvesting plants and animals. These changes have 



Table 2-1 : Summary of mean annual flow of the Nueces River into the Nueces Estuary (1 940 to 1 996)' and upper 

 Nueces Delta (1940 to 1999)^ Time periods in both studies were based upon the construction dates of large reservoirs in 

 the watershed. 



2-18 ♦ Study Area 



