METHODS 



As previously discussed, the Nueces Delta has been a dynamic system in the past, experiencing changes from 

 both natural and man-made causes. During the past 60 years, the major attributes of the delta Hke general 

 topography, railroad crossings and channel locations have not changed significandy, while smaller 

 modifications, such as flooding thresholds, have occurred. However, lacking the information necessary to 

 define more subde changes in the study area or to analyze their effects, the assumption was made for the 

 purposes of this analysis that the delta's physical characteristics during the entire period under study have 

 essentially resembled those observed in the field during 1993. 



Data Sources 



Available data included daily discharge and stage 

 records for several gaizges on the Nueces River 

 operated and maintained by the United States 

 Geological Survey (USGS) (Figure 3). 



Mathis Gauge 



Station 08211 000, the Nueces River Near Mathis, 

 Texas (Mathis gauge), is located on the Nueces River 

 0.96 km downstream of Wesley Seale Dam (Lake 

 Corpus Christi). The gauge receives flow from 

 approximately 43,512 km^ or 98.4%, of the 

 watershed. Daily discharge and stage data were 

 available from August 1 939, to present. The 

 maximum daily stage value recorded at the Mathis 

 gauge was approximately 3,546 cubic meters per 

 second (mVs) (125,000 cfs) on September 25, 1967. 



Calallen Gauge 



Station 08211500, the Nueces River at Calallen, 



Texas (Calallen gauge), is located on the Nueces 



River 0.64 km upstream from Calallen Diversion 



Dam, approximately 2.3 km upstream from the 



bridge on Interstate Highway 37 and some 54.6 km 



downstream from the Mathis gauge. This gauge 



receives flow from approximately 44,071 km^, or 99.7% of the watershed. Unpublished daily stage data were 



available for the period of April 1920 through July 1950 from the USGS District office in Austin, Texas. 



Reliable daily discharge and stage data are published from October 1989, to present. The Calallen gauge is 



operated as a low-flow gauge, with daily discharges published only for days when instantaneous maximum 



discharge does not exceed 72.8 m^/s (2,570 cfs) (Gandara et al. 1996), which corresponds to a daily stage value 



of about 2.48 m (8.14 ft). However, higher daily stage values up to 4.13 m (13.55 ft) were available from the 



unpublished record. Datum of the gauge is 0.84 ft above mean sea level. 



Rincon Gauge 



Station 0821 1503, Rincon Bayou Channel near Calallen, Texas, (Rincon gauge) was installed and operated by 

 the USGS at the request of the U.S. Bureau of Reclamation as part of their Rincon Bayou Demonstration 

 Project. The objective of this project was to increase the opportunity for freshwater flow events into the upper 

 Nueces Delta. The main feature of the demonstration project was a 305-meter (m) overflow channel excavated 

 from the Nueces River at the point of natural diversion to a small headwater of Rincon Bayou. The Rincon 

 gauge is located in this headwater channel approximately 310 m downstream from the north bank of the 

 Nueces River. Daily stage, discharge and precipitation data are available from May 1 996 through December 

 1999. The maximum daily stage value recorded at the Rincon gauge was 2.21 m (7.25 ft) on October 21, 1998. 

 Datum of the gauge is at mean sea level. 



Figure 3: Diagram of the lower Nueces River 

 showing the location of selected stream flow 

 gauging stations.. 



C-6 V Analysis of the Historic Flow Reffme of the Nueces River into the Upper Nueces Delta 



