freshwater into the tidal flats. The first ocairrence was 

 during Event 16, when such discharge was observed in 

 the field, and the second was during Event 25, when 

 the road structure at the north end of the channel was 

 washed out into the tidal flats (Figure 3-15). Based 

 upon comparable event stages, super-elevations and 

 flow volumes, it was strongly suspected that the 

 Rincon Overflow Channel also passed some amount of 

 diverted fresh water during Events 17, 18 and 36, 

 although this was not visually verified. 



Figure 3-15: The Rincon Overflow Channel. The road 

 crossing structure, as shown from the air during Event 16 

 in June 1997 (above), w/as washed out during Event 25 in 

 October 1998, as shown in June 1999 (below). The 

 HOPE culverts (foreground of the lower photo) were 

 24"-diameter, and the livestock (background of the 

 lower photo) were Red Brangus. 



Ptiotos courtesy of the Bureau of Reclamation. 



Figure 3-16: The low water crossing at the head of the 

 upper Rincon Bayou channel. The integrity of this 

 structure, although significantly over-topped during Event 

 25 (October 1998), remained unchanged throughout the 

 demonstration period. Each HOPE culvert was 

 36"-diameter. The photo was taken on June 1999. 



Photos courtesy of thie Bureau of Reclamation. 



Low Water Crossing 



The low water crossing at the head of Rincon Bayou 

 performed exceptionally well. All flows diverted from 

 the river (either naturally or through the Nueces 

 Overflow Channel) passed through this structure 

 (Figure 3-16). On at least one occasion (Event 25), a 

 significant amount of water passed over the top of the 

 crossing, with no damage visible. At the end of the 

 demonstration period, the structure was essentially the 

 same as at the beginning. 



SUMMARY 



The demonstration project features significandy 

 lowered the minimum flooding threshold of the upper 

 Nueces Delta, and thereby increased the opportunity 

 for larger, more frequent hydrographic events. Based 

 on observations and data analysis during the 

 demonstration project, such events were categorized 

 into three general types: small "exchange" events, 

 "positive-flow" events and "tidal flat inundation" 

 events. 



3-22 ^* Hydmgraphy 



