Developing a Daily Stage Record for the Nueces River at the Point of Diversion 



The analysis of the Nueces River's flow regime and associated delta flooding characteristics over the past 60 

 years required a daily stage record for the Nueces River at the point of natural diversion, which was not 

 available. The "point of natural diversion", for the purposes of this investigation, was generaUy defined as the 

 2,000-m reach of the north bank of the Nueces River from Interstate Highway 37 downstream to where it 

 sharply bends to the south (Figure 4). In lieu of actual gauge data for this reach of the river, an artificial stage 

 record was developed from correlations of data collected at other gauges in the lower Nueces watershed. This 

 simulated daily record was then used to generally represent flow conditions at the point of diversion. 



Figure 4: The "point of diversion" along the north banl( of the Nueces River. The location of the five 

 natural depressions in the river bank which contribute to delta inflow during a flood event are indicated by 

 arrows (Bureau of Reclamation 2000). 



Although measures were taken to minimize the error Ln the manufactured data record, the accuracy of specific 

 quantitative values estimated by this method is debatable. However, this method does provide a reasonable 

 estimate of general hydraulic conditions in the Nueces River and upper delta during the period under review, 

 and therefore was considered to be acceptable for use in analyzing qualitative {i.e., relative) differences in flow 

 event characteristics. Furthermore, this analysis was exclusively focused on the upper Nueces Delta, or that 

 northern portion of the delta primarily influenced by Rincon Bayou. No attempt was made to characterize the 

 flow regime of the lower (or southern) portions of the delta. 



The procedure used to create a daily record of discharge into the upper Nueces Delta from daily Mathis 

 discharge data included two basic steps. First, gauge data was used to correct and correlate Mathis discharge 

 with stage values at Calallen (the Mathis gauge provided the longest reliable daily flow and stage data for the 

 longest continuous period of record on the lower Nueces watershed, or from August 1939 to present). Second, 

 gauge data was used to correlate daily Calallen stage with stage values at the point of diversion. 



Appendix C ♦ C-7 



