Figure 10.12. Rillito River system vicinity map.
Undeveloped land in the study area generally has little protective cover and supplies large
quantities of sediment to the river system. However, extensive erosion control measures
established for urban development and the creation of impermeable areas in these tributaries
has reduced the sediment supply to the river system. As urbanization continues there will be a
long-term decrease in sediment supply that will have a significant influence on the
geomorphology of the river system.
The four bridge sites in the study area are at Dodge Boulevard, Swan Road, Sabino Canyon
Road, and Tanque Verde Road (Figure 10.12). Measures have been taken at Craycroft Road
to stabilize the crossing during the low flows and, as a result, the crossing is acting as a grade
control on Pantano Wash. Stabilization measures have not been successful on the north side
of Craycroft and no grade control has formed. Complex hydraulic conditions exist at the
confluence of Tanque Verde Creek and Pantano Wash during the 100-year flood. Divided flow
occurs with flood water spilling laterally into Pantano Wash from Tanque Verde Creek during a
flood from that watershed, or flood water spills to Tanque Verde Creek during a flood from the
Pantano watershed.
The bridges across the Rillito River and Tanque Verde Creek span a variety of channel
conditions. The sedimentation and erosion processes due to the proposed bridges will depend
on the extent to which the bridge influences the hydraulic conditions in the river (primarily the
velocity and depth). Conversely, the changing form of the channel due to lateral migration or
long-term changes in the channel profile can alter the hydraulic conditions at the bridge. The
Dodge Boulevard bridge is assumed to be the downstream control for the study reach. This
assumption is valid because the bridge crosses a channelized section of the Rillito River which
has little influence on the water surface elevation in the channel for the 100-year flood. The
downstream boundary hydraulic condition is assumed to be uniform flow.
Swan Road also crosses the Rillito River at a channelized section and has little effect on
upstream water surface. Craycroft Road is one of two crossings discussed in detail later. The
Sabino Canyon bridge crosses the defined channel on the Tanque Verde Creek. At the bridge
10.18
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