Bayou became negative immediately after stage in the 

 river began to receded beginning October 13 

 (Figure 3-8). 



Due to significant runoff from the large amounts of 

 tropical moisture and associated precipitation in the 

 upper Nueces Basin during this period, the Nueces 

 River again began to rise, cresting on October 21 

 (Event 25). This crest resulted in an estimated daily 

 flow rate of 73.6 m'/s (2,600 cfs) in the Nueces River 

 at Calallen, the highest flow rate attained during the 

 demonstration period. The corresponding water 

 elevation in Rincon Bayou was also the highest daily 

 stage recorded during the study, 2.22 m (7.28 ft msl), 

 which was 0.48 m (1.56 ft) higher than the next highest 

 event daily peak (Event 36). Because of this. Event 25 

 was the only event to witness the Nueces River 

 meaningfully exceed the natural {i.e., without-project) 

 diversion threshold of the upper Nueces Delta, which 

 was 1.64 m (5.40 ft) msl. As a result, the estimated 

 amount of delta inflow over the natural river bank 

 (1,204 10' m\ or 976 acre-ft) was about 50% as much 

 as that which was gauged through the overflow 

 channel (2,560 10' m', or 2,075 acre-ft). It was during 

 this event that the road crossing at the lower end of the 

 Rincon Overflow Channel washed out (Figure 3-12). 



Events 26 and 27 concluded the fall occurrence of 

 1998, resulting in two more smaller peaks in river and 

 diversion flows as the greater watershed finally drained 

 the accumulated runoff of the preceding months. 



FaU1999: Events 35 and 36 



Hurricane Bret was the first major hurricane of the 

 Adantic 1999 season (Figure 3-13). The storm formed 

 in the southern Gulf of Mexico and moved slowly 

 northward along the Mexican Coast. As it approached 

 south Texas, it rapidly intensified into a Category 4 

 hurricane. Landfall was made as a Category 3 storm on 

 August 23, in a remote area between Brownsville and 

 Corpus Christi (Event 35). The storm surge from Bret 

 was substantial, and combined with the 14.43 cm 

 (5.68 inches) of local precipitation that fell on August 

 22 and 23, the Rincon gauge recorded a maximum 

 elevation of 1.76 m (5.79 ft) msl (August 23). This 

 value was the highest value recorded during the study 



Figure 3-12: Discharge into the tidal flats area through 

 the road crossing at the north end of the Rincon 

 Overflow Channel during Event 16 (June 27, 1997). 



Each of the 10 corrugated HOPE culverts shown were 24"- 

 diameter. This structure was subsequently washed out 

 during Event 25 (October 1998). 



Photo courtesy of the Bureau of Reclamation. 



period without a corresponding flow ev^ent in the 

 Nueces River. Once the low pressure system had 

 moved on-shore, the surge tide and local runoff in the 

 upper delta began to drain out, resulting in a net 

 negative flow through the overflow channel for Event 

 35 (Figure 3-9). 



As a result of heavy rainfall in the watershed associated 

 with Hurricane Bret, particularly in the southwestern 

 portion, the Nueces River again responded with a large 

 hydrograph beginning on September 5 (Event 36). 

 The amount of diverted flow through the overflow 

 channel was the second largest recorded for any event, 

 with a net flow of 1,052 10' m' (853 acre-ft) over 

 17 days. The salinity of Nueces Bay, which had already 

 been lowered by the landfall of Hurricane Bret some 

 three weeks before, continued to decrease as a result of 

 the event. 



Chapter Thm ♦ 3-19 



