Table 10.9. Equilibrium Slope Calculations, Dominant Discharge.
Slope in ft/ft
Location
Actual
Present
25 Percent
50 Percent
Supply
Reduction
Reduction
Cross-Sections 32-47 (Pantano)
0.0060
Too much gravel mining to accurately estimate
Cross-Sections 31-24 (Pantano)
0.0035
Reach assumed in equilibrium at present slope
(supply reach)
Cross-Sections 47-54
0.0033
Reach assumed in equilibrium at present slope
(Tanque Verde)
(supply reach)
Cross-Sections 46-45
0.0048
0.0032
0.0026
0.0020
(Tanque Verde-Sabino)
Cross-Sections 44-27
0.0036
0.0036
0.0030
0.0023
(Tanque Verde)
Cross-Sections 26-23
0.0043
0.0033
0.0027
0.0023
(Rillito Craycroft)
Cross-Sections 22-18 (Rillito)
0.0037
0.0032
0.0026
0.0020
Cross-Sections 17-14
0.0043
0.0032
0.0026
0.0020
(Rillito Swan Road)
Cross-Sections 13-1 (Rillito)
0.0039
0.0031
0.0025
0.0020
Meander wave length, channel width and radius of curvature ( λ, B, and rc) pairs were plotted
for each meander loop. These points were plotted on logarithmic scales and on linear scales.
Straight lines were fitted and the following equations were obtained and adopted for the lower
13 miles (21 km) of the Tanque Verde Creek:
λ = 2.6 rc
λ = 2.75 B1.35
rc = 1.06 B1.35
These relationships are used to determine appropriate channel widths and bend shapes at the
Sabino Canyon Road Bridge site.
Sabino Canyon Road Bridge (Figure 10.15) is currently located on a bend with a curvature that
creates several problems. At low flows, scour occurs at the outside of the bend (south side)
because of high velocity and secondary currents. This phenomena is evident in the present
channel cross section under the bridge. At flood flows, the problem is nearly the opposite. The
north side of the bridge is attacked because of the tendency of the thalweg to straighten in the
bend. The amplitude of the meander bend is 300 ft (91 m). Therefore, the lateral migration
tendency is on the order of 300 ft (91 m).
These facts point to the necessity for engineering control measures to be taken at Sabino
Canyon Road Bridge in order to prevent future failure of the structure from lateral migration.
Possible measures are bank stabilization and channelization.
10.2.4 Level 3 - Sediment Routing for the 100-Year Flood
The long-term trends of the Tanque Verde, Pantano, Rillito River system were determined
using a sediment routing procedure. This analysis determined the aggradation and
degradation for subreaches in the respective river systems, based on sediment supply from the
upstream reaches and local hydraulic conditions throughout the system. Subcritical hydraulic
conditions were assumed for all backwater computations.
10.31
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