on Rincon Bayou near Calallen (Station 0821 1503) (Rincon gauge) of 0.81 for the 3 years of coincident data. 

 After May 15, 1996, daily precipitation was obtained by the Rincon gauge. 



Flow (Nueces River) 



Daily values for flow in the Nueces River were obtained from the U.S. Geological Survey (USGS) on the 

 Nueces River at Calallen (Station 08211500) (Calallen gauge). Because no reliable field observations of 

 discharge values were available above 77.87 m'/s (2,750 cfs), all daily flow values in excess of 77.87 m'/s were 

 estimated by extrapolation (Irlbeck and Ockerman 2000). 



Flow (Rincon Bayou) 



For dates before the opening of the Nueces Overflow Channel (October 26, 1995), daily flow data into Rincon 

 Bayou from the Nueces River were estimated from daily stage values recorded at the Calallen gauge using the 

 method described by Irlbeck and Ward (2000). No daily data were available from the period of October 26, 

 1995, through May 15, 1996, when the Rincon gauge was installed. From that date through the end of the 

 record, flow data reported for Rincon Bayou was the total net daily flow gauged at the Rincon gauge. 



It is important to note that, during the demonstration period, the Nueces River did not exceed the natural 

 flooding threshold for the delta, which is 1.71 m (5.60 ft) (Bureau of Reclamation 2000), except for on three 

 occasions. This means that, except for these four events (Events 16, 18, 25 and 36), the only water exchanged 

 between the Nueces River and Rincon Bayou passed through the Nueces Overflow Channel. During the three 

 excepted events, an additional amount of water entered Rincon Bayou naturally via the low depressions along 

 the bank of the river, and was estimated using the hydraulic model developed by Reclamation (2000). 



Stage 



Water level data for the Nueces Bay and Rincon Bayou were obtained from the Texas Coastal Ocean 

 Observing Network (TCOON) marine monitoring system of Texas A&M University-Corpus Christi Conrad 

 Blucher Institute (CBI) and the USGS Rincon gauge, respectively. The super-elevation of water levels, 

 determined by subtracting the Nueces Bay stage from the Rincon Bayou value, was used to determine the 

 predominant influence on stage in upper Rincon Bayou. On an instantaneous basis, the super-elevation is the 

 direct force for discharge through the Nueces Overflow Channel. 



Salinity 



Salinity data were obtaitted from the CBI SALT03 gauge of the TCOON system. 



Observations 



Freshwater Flow 



A principal objective of this demonstration project was to increase the opportunity for partial diversion of flow 

 events in the Nueces River through the Nueces Overflow Channel into Rincon Bayou and the upper delta. The 

 project would thereby periodically increase water levels and inundate regions of the upper marsh, while at the 

 same time reduce salinity concentrations, all of which were considered to be ecologically beneficial. Since the 

 purpose of the demonstration project was to divert a portion of a flood hydrograph on the Nueces through the 

 diversion channel, a logical inquiry was the proportion of such a flood so diverted. The bulk event data can be 

 used to address this question. 



Upon examination of the relation between the total flow voliune in the Nueces River (for events which met the 

 criteria) and in the Nueces Overflow Channel, it became obvious that there was a general association between 

 the two. The volume diverted increased generally with the flow in the river, and the actual proportion of the 

 flow amount diverted was on the order of 2 percent of that in the river (Figure 3). But this relation, such as it 

 was, evidenced considerable scatter. In further analysis, the data was segregated by water level in Rincon Bayou 

 at 0.3-m (1-ft) intervals. Within each class of water levels, the volume transported through the Nueces 

 Overflow Channel proved to be substantially independent of the volume in the Nueces River. This was 

 somewhat surprising. 



B-8 ♦ Hydrograph)/ of the Nueces Delta and Estuary: 1992-1999 



