c 



CO 



O 



ro 



<D 

 05 

 TO 



CD 



Q 



17 



16 



15 



14 



13 



12 



11 



10 



9 



8 



7 



6 



5 



4 



3 



I I ^* 



::=^^» :: -' - 



20000 40000 60000 80000 100000 



Corrected daily discharge at Mathis (cfs) 



120000 



Figure 5: Regression analysis of corrected daily Mathis discharge and daily stage at Calallen. 



Note; 1 (rfs = 0.0283 m'/s; 1 ft = 0.3046 m 



Correlating Calallen Stage to Estimated Stage at the Point of Diversion 



Stage or flow data for the Nueces River downstream of Calallen Dam is extremely limited, but were available 

 from the Rincon gauge for a period of approximately i'A years. This gauge was located in the headwater 

 channel of Rincon Bayou, approximately 310 m downstream from the point of natural diversion of Nueces 

 River. Therefore, the concurrent period shared by the Calallen and Rincon gauges (daily flow and stage records 

 from May 1996 through December 1999) was used to correlate Calallen stage to estimated stage at the point of 

 diversion. This included one modification to the original Rincon data set prior to the correlation. 



At higher stage values, the Rincon gauge experienced a minor head loss during discharge events, which was 

 estimated to be as much as 0.08 m (0.25 ft) by the Bureau of Reclamation using a hydraulic model (2000). The 

 Rincon stage data was therefore corrected using this model to represent stage at the point of natural diversion 

 before being correlated with Calallen gauge data. 



Once the Rincon data set had been corrected, the relationship between daily Calallen stage values and corrected 

 daily stage data at the point of diversion was determined through linear regression (Figure 6). Not used were 

 data from several anomalous stage events recorded at the Rincon gauge (October 1996, November 1996, April 

 1997, June 1998, and May 1999) which were not associated with discharge at Calallen. In addition, data from 

 two previous maximum stage events were used as estimates of the extreme conditions. First, during the flood 

 of 1919, the maximum stage of the Nueces River recorded at Calallen by the USGS was 4.16 m (13.65 ft), and 

 at the Interstate Highway bridge (representing point of diversion) was 3.75 m (12.3 ft) (Texas State Highway 

 Department 1956). Second, during the 1967 flood, the maximum stage recorded at Calallen was 5.02 m (16.48 

 ft) (Corpus Christi Times 1967), and at the bridge was 4.63 m (15.2 ft) ^exas State Department of Highways 

 and Public Transportation 1983). 



This relationship therefore allows the use of Calallen daily stage data as the independent variable to solve for the corresponding 

 estimated daily stage at the point of natural diversion. The entire estimated Calallen stage data set was then converted 

 to estimated stage at the point of diversion using this relation. 



Appendix C ♦ C-9 



