periods of salinity stress have limited active growth and 

 reproduction in the Nueces Delta, leading to lower 

 biological productivity and less species diversity. 



This demonstration project was designed to increase 

 the opportunity for freshwater flow events &om the 

 Nueces River into the upper Nueces Delta assuming 

 that resultant hydrographic changes would beneficially 

 affect the ecology of the upper delta. Reclamation 

 initiated the demonstration project in 1993 with the 

 excavation of two overflow channels and then 

 monitored the changes in hydrography, the water 

 column, benthic communities and vegetation 

 communities. 



CHANGES IN HYDROGRAPHY 



During the 50-month period when the overflow 

 channels were open, over 8,810 10' m' (7,142 acre-ft) 

 of water was diverted from the Nueces River into 

 Rincon Bayou. Of this total amount, only about 

 1,204 10' m' (976 acre-ft) wovdd have been diverted 

 without the demonstration project features. Therefore, 

 the total volume of freshwater inflow to the upper 

 Nueces Delta was increased by about 732% from what 

 would have occxirred without the project. 



In addition to increased inflow, the demonstration 

 project features also increased the distribution of firesh 

 water within the tidal flats of the upper delta. On five 

 different occasions during the demonstration period, 

 the tidal flats of the upper marsh were supplied with 

 diverted fresh water. Without the project features, no 

 natural inflow event would have direcdy freshened 

 these areas. 



These changes occurred because the demonstration 

 project features lowered the minimum flooding 

 threshold for the Nueces River firom 1.64 m (5.4 ft msl) 

 to about m mean sea level. This change not only 

 allowed more frequent river diversions into Rincon 

 Bayou and the upper delta, but also provided the 

 opportunity for other non-riverine elements Uke wind 

 and tide to force frequent exchanges between the upper 

 delta and the Nueces River. As a result, near continual 

 (daily) exchange between the river and delta was 



observed during the demonstration period. Before the 

 project, such interactions were limited to only 

 extremely infrequent river inflow events. 



EFFECTS ON SALINITY 



The demonstration project gready lowered short-term 

 salinity concentrations in the upper and central 

 segments of Rincon Bayou, as indicated by results of 

 the hydrographic analysis (Chapter 3) and subsequent 

 biological response analyses (Chapters 4 through 6). 

 The demonstration project also affected the overall {i.e., 

 long-term) salinity gradient of Rincon Bayou. 

 Unpublished long-term saUnity data from selected 

 stations in the Nueces Delta and Nueces Bay were 

 obtained from Dr. Terry VCTiidedge (University of 

 Alaska Fairbanks) and Dr. Paul Montagna (University 

 of Texas Marine Science Institute) (Figure 7-1).). 

 These data covered the period of January 1992 through 

 December 1999 and were made available from projects 

 sponsored by the Texas Water Development Board, 

 City of Corpus Christi, Corpus Christi Bay National 

 Estuary Program and Texas Sea Grant Program. This 

 8-year interval was divided into two nearly equal 

 periods before and after the Nueces Overflow Channel 

 was completed (October 26, 1995). The before-project 

 period was about 3.8 years long, and the after-project 

 period was about 4.2 years long. 



The average salinity at each selected station was 

 calculated for each month. Monthly averages at each 

 station were then averaged for each period before and 

 after the demonstration project to smooth the year-to- 

 year variation and compare means. These values were 

 then plotted along their respective channel segment 

 lengths, beginning at where the Interstate Highway 37 

 (IH 37) bridge crosses the Nueces River to a point in 

 Nueces Bay just west of White Point (Figure 7-2). 



In the upper and central segments of Rincon Bayou, 

 the average salinity gradient changed dramatically after 

 the opening of the Nueces Overflow Channel. During 

 the period before the demonstration project, there was 

 no regular interaction with the Nueces River and 

 salinity concentrations in the delta were highest in 

 upper Rincon Bayou (Figure 7-2a). This condition may 



7-2 ^ Synthesis and Conclusions 



