Abstract 



The Rincon Bayou Demonstration Project significantly lowered the minimum flooding threshold of 

 the upper Nueces Delta, thereby increasing the opportvinity for larger, more frequent diversions of 

 fresh water from the Nueces River. During the 50-month demonstration period, the amount of 

 fresh water diverted into the upper Nueces Delta was increased by about 732%. Five fireshwater 

 inflow events were sufficient to activate the project's Rincon Overflow Channel and inundate, to 

 varying degrees, the tidal flats of the upper delta. These tidal flows would not have otherwise been 

 direcdy fireshened. As a result, in a relatively short period of time (only 4.2 years after the opening of 

 the project's Nueces Overflow Channel), the average salinity gradient in the upper delta reverted to a 

 more natural form, with average salinity concentrations in upper Rincon Bayou becoming the lowest 

 in Nueces Delta. 



The effects of the demonstration project on the ecology of Rincon Bayou and the upper Nueces 

 Delta were positive to the environment. Single-celled plant communities in the water column 

 (phytoplankton) and on the surface of the sediments (microphytobenthos) evidenced increases in 

 primary productivity with the reduction of salinity concentrations. Benthic communities (composed 

 of bottom-dwelling organisms) evidenced increases in abundance, biomass and diversity. And, 

 vegetation communities evidenced increases in plant cover and decreases in bare area. In summary, 

 it was observed that freshwater inflow controlled, to a great extent, the ecological fiinction of the 

 upper delta ecosystem by regulating critical biological mechanisms. 



A significant degree of ecological function was returned to the Nueces Delta and Nueces Estuary 

 ecosystems by the demonstration project. Prior to the project, persistendy high salinity 

 concentrations severely inhibited the function of the Nueces Delta, and the delta's natural 

 contribution to the greater estuary ecosystem was limited to infrequent periods when natural flow 

 events occurred. With the restored regular interaction between the Nueces River and Rincon Bayou, 

 fresh water and nutrients were more consistendy introduced into the upper delta. As a resvilt, 

 estuarine habitat in the delta component of the Nueces Esmary improved in both quality and 

 quantity, and foraging opportunities for many estuarine species were increased. 



