Nueces River into the vicinity of the upper delta. 

 However, as became evident, other hydro- 

 meteorological processes would also effect similar 

 responses in these variables. 



Criteria for Event Delineation 



After inspection of the entire period of record on both 

 intertidal and intratidal scales. Ward (2000) formulated 

 criteria to identify an event based upon the separate 

 hydrographic behaviors of each of the key response 

 parameters. These response variables included stage 

 (in Nueces Bay, in Rincon Bayou and the super- 

 elevation of Rincon over Nueces Bay), flow (in the 

 Nueces River and in Rincon Bayou) and salinity (in 

 Nueces Bay) (Table 3-2). It should be emphasized that 

 these criteria were ultimately arbitrary but were utilized 

 to ensure an objective selection of candidate events for 

 analysis. Precipitation was not treated as a separate 

 hydrographic variable, though it was certainly an 

 important hydrographic element in understanding the 

 response of the delta ecology. The reason for its 

 exclusion as a defining parameter was that it provided 

 no in forma tion/)«'rj'(? on the response of the Nueces 

 Estuary or Delta. A similar argument was made for the 

 exclusion of wind as a defining criterion. 



Once these criteria were established, the daily data for 

 the period of study was manually inspected (Ward 

 2000). Individual occurrences within the record which 

 met at least one of the six criteria were identified as 

 hydrographic events. Then, for each event, the 

 24-hour mean data for aU hydrographic variables 

 during the event were separated and transferred for 

 individual analysis. The duration period for each event 

 was at least that for which the defining criterion was 

 satisfied, though often a longer event period was 

 chosen to be sure that the complete response of the 

 bay or delta was included in the analysis. When several 

 hydrographic events overlapped (i.e., when several 

 variables each satisfied criteria separately and 

 simultaneously), the event duration was at least the 

 period from the first occurrence of the criterion 

 threshold for the earliest parameter to at least the last 

 such threshold for the latest parameter. 



The greatest difficxilty reported in separating such 

 events was met when a time series of events occurred 

 in which the response of one parameter overlapped 

 that of the next. For example, a series of river 

 hydrographs might occur, each of which raised the 

 Rincon stage or CalaUen flow above the threshold 

 defining an event, and a new surge of inflow occurred 



Table 3-2: Criteria used to define hydrographic events in the data record by response variables. 



Source: Ward 2000. 



Response 

 Parameter 



Location 



Defining Criteria of a Hydrographic Event 



Flow 



Stage 



Salinity 



Nueces River A 24-hour mean (daily) flow in the Nueces River at Calallen exceeding 



14.2 mVs (500 cfs). 



Rincon Bayou A 24-hour mean (daily) flow in Rincon Bayou, either positive or negative, 



exceeding 0.28 mVs (10 cfs). 



Nueces Bay A 24-hour mean (daily) stage in the water elevation of Nueces Bay exceeding 



0.30 m (1 .0 ft), referenced to the consistent CBI datum from Ward (1997), 

 established by "empirical leveling". 



Rincon Bayou A 24-hour mean (daily) stage in the water elevation of Rincon Bayou exceeding 



0.61 m (2.0 ft), relative to Rincon gauge datum, which is 422 cm above the 

 consistent datum for CBI gauges. 



Super-elevation The difference of Rincon Bayou minus Nueces Bay daily stage values 

 exceeding 0.15 m (0.5 ft), referenced to common datum. 



Nueces Bay Change in salinity concentrations of Nueces Bay exceeding 5 ppt over a five 



day period. 



Chapter Three ♦ 3-5 



