Table 10.8. Rillito River Near Tucson, Arizona Log-Pearson Type III Frequency Analysis
by USGS.
95 Percent Confidence Limit
Exceedance
Return
Expected
(One-Sided Test)
Period (yr)
Discharge (cfs)
Lower (cfs)
Upper (cfs)
0.5000
2
5,000
4,240
5,800
0.2000
5
9,300
7,670
11,100
0.1000
10
12,500
10,100
15,600
0.0400
25
17,200
13,300
22,000
0.0200
50
21,100
15,800
27,300
0.0100
100
25,200
18,400
33,000
0.0050
200
29,800
20,900
39,200
0.0020
500
35,700
24,400
47,800
Figure 10.16. Flood events at Rillito River near Tucson, Arizona (drainage area 915
square miles).
Hydraulics. A complete rigid boundary hydraulic analysis was conducted prior to the moveable
bed analysis. Water surface profile calculation from Dodge Boulevard to Agua Caliente Wash
(Figure 10.12) was conducted using the Corps of Engineers HEC-2 program (today the Corps'
HEC-RAS program would be used). The cross sectional data were modified to reduce the
number of cross-sections and make the spatial resolution of the water surface computation
compatible with the sediment routing model. The main channel roughness was reduced to
near the lower limit of the river flow regime expected during the 100-year flood. The hydraulic
conditions are predominantly subcritical up to Sabino Creek. The reach from Sabino Creek to
Agua Caliente Wash increases in gradient and a mix of subcritical and supercritical hydraulic
conditions is possible.
10.25
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