Estuary, even though it was stable in the Aransas Bay 

 ecosystem to the north and the upper Laguna Madre to 

 the south (Montagna et al. 1998). 



Because of contention regarding the amount of fresh 

 water dedicated to the bays and estuary from the 

 reser\'oir system, releases had not been made for that 

 purpose since Choke Canyon Reser\^oir filled. In 1992, 

 the Texas Natural Resources Conservation 

 Commission (TNRCC) implemented an operating plan 

 requiring minimum mandator)' inflows on a monthly 

 schedule totaUng 186,274 10^ m' (151,000 acre-ft). As 

 part of the same order, TNRCC also created the 

 Nueces Estuary Advisory Council to provide oversight 

 of the releases and monitor the operating plan, and to 

 make recommendations for improving the plan. In 

 April 1995, the original TNRCC order was revised to 

 adopt a "target" minimum monthly inflow plan instead 

 of a mandatory inflow amount. This change, which 

 resulted in an annual inflow target of 112,258 10^ m^ 

 (91,000 acre-ft), was intended to mimic natural 

 hydrographic conditions in the Nueces Basin while 

 providing some relief to the water customers of the 

 resen'oir system. 



THE RINCON BAYOU 

 DEMONSTRATION PROJECT 



Beginning about 1993, a consortium of local, State and 

 Federal entities began investigating alternatives to 

 restore fresh water to the greater Nueces Estuary. In 

 1993, as part of this initiative, the Reclamation 

 undertook a temporary demonstration project to 

 provide detailed scientific information regarding the 

 freshwater needs of the delta and its response to 

 changes in freshwater inflows. The Rincon Bayou 

 Demonstration Project had two primary objectives: 



1) To increase the opportunity for natural 

 freshwater flow events into the upper Nueces 

 Delta; and 



2) To monitor any resulting changes in the hydro- 

 graphy and biological productivity of the delta. 



Project Features 



The area selected for the demonstration study 

 encompassed the northwestern portion of the upper 

 Nueces Delta, or that area generally north of Rincon 

 Bayou and west of the eastern-most railroad crossing 

 (Figure 1-4). This area represents both the historic 

 location of river inundation events and the western 

 limit of the Nueces Estuary {i.e., the tidally influenced 

 portions of Rincon Bayou and a large area of tidal 

 flats). 



Water Diversion 



Reclamation decided on a final demonstration project 

 design after reviewing several different alternatives. 

 The selected alternative provided an uncomplicated 

 means of increasing the opportunity for freshwater 

 diversion and distribution in the upper delta, while 

 preser%'ing the natural "event" mechamsm to which the 

 system had adapted. The physical aspects of the 

 project included two principal features: the Nueces 

 Ch^erflow Channel and the Rincon Overflow Channel 

 (Figure 1-4). 



The primary feature of the demonstration project was 

 an overflow channel (Nueces Overflow Channel) 

 excavated from the Nueces River to the headwaters of 

 Rincon Bayou (Figures 1-4 and 1-5). The channel was 

 located approximately 60 m downstream of the 

 Interstate Highway 37 (IH 37) bridge along the north 

 bank. The design dimensions of the Nueces Overflow 

 Channel were approximately 274 m long and 12 m 

 wide, with a bottom elevation of 0.6 m (2.0 ft) mean 

 sea level (msl). This bottom elevation was selected so 

 as to prevent regular tidal exchange between the 

 Nueces River and the upper delta. However, early into 

 the demonstration period, the channel's effective 

 bottom elevation was lowered by flow events and tidal 

 exchange to approximately mean sea level. Minor 

 excavations were also made at two sites along the 

 headwater channel of Rincon Bayou to remove 

 channel-constricting sediment deposits, thereby 

 allowing a higher diversion volume during flood events. 

 Construction of the channel was completed 

 on October 26, 1995. The purpose of the Nueces 

 Overflow Channel and associated channel 



1-4 



Introduction 



