WSP08097

• File Number: 8507
• Description: Rio Grande Project
• State: CO
• Basin: Rio Grande
• Date: 2/1/1961
• Title: Final Report Hydralic Model Studies
• Water Supply Pro - Doc Type: Report/Study

In the field system, that is in the Rio Grande in the reach from

Langtry to Del Rio, it is visualized that a condition varying between

the two extremes cited above probably occurs. ~ing floods, tributaries

may contribute considerable q.uantities of alluvial material to the main

river. When the flow in the tributaries recede significantly and sedi-

ment inflow to the main river stops, the transport capacity of the resi-

dual flow in the main river is probably still sufficient to transport the

available fine sediment material downstream over the structure. It is pos-

sible also that an unbalance may occur in nature as it did in the

2-ft flume, where the sediment supplied by a number of tributaries may

eq).1al or exceed the total transport capacity of the main river thus caus-

ing deposition in the river channel. This is not likely to occur in the

reach of the Rio Grande from Langtry to Del Rio, especially with fine sedi-

ment. It is possible for this to occur, however, with large materials

(cobbles and boulders) and if the location of the structure in the river

is very near heavily contributing tributaries.

The hydrograph studies also indicated variation of the discharge

coefficient with both discharge and upstream aggradation. (Note changes

of C and p with time on Fig. 11). Results of studies conducted with

changing values of p, where p is the height of the weir above the up-

stream bed, are given in Fig. 12.

The values of C vary with both p and unit discharge q, for

q less than 1.3 cfs per ft in the model (approximately 14.5 cfs per ft

prototype). When the bed was level with the crest, C remained essen-

tially constant. The change in the discharge coefficient was probably

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