Spatial Design and Channel Geometry. In the quantitative geomorphic analysis, groups of
cross sections were aggregated to form a typical cross section for a study reach. The
geometric properties (area, wetted perimeter, top width, and hydraulic radius) of this section
are determined for a series of depths. Normal depth for a given discharge, channel roughness
and slope are then calculated and the hydraulic parameters (velocity and hydraulic depth) are
used in the sediment transport relationship to determine the transport capacity in the reach. An
A water surface profile calculation is made based on the sections utilizing HEC-2 (HEC-RAS).
Hydraulic conditions in the main channel and overbank areas are based on output from HEC-2
Bed Material Size Distribution. Sediment size is one of the most important parameters used in
evaluating sediment transport. A thorough sediment sampling survey was conducted on the
river system, consisting of 41 bed material samples. Variation of the size distribution within
these segments of the river did not follow an identifiable trend, and therefore an average size
distribution was used and the variation from the average size distribution was assumed to be
sampling error. Three size distributions were used to cover the river segments from Dodge
Boulevard to Pantano Wash (including Pantano Wash), Pantano Wash to Sabino Creek and
Sabino Creek to Agua Caliente Wash. Figure 10.21 shows the size distributions used for
design on various segments of the river system. The size distribution of Pantano Wash is
included to illustrate its similarity to the Rillito River size distribution.
Figure 10.21. Rillito-Pantano-Tanque Verde bed sediment distribution.
A large percentage of sediment falls in the coarse sand and fine gravel range with less than 10
percent classified as medium gravel. Very coarse gravels are not present. From an analysis
based on Shields' criteria, all sizes present can be easily transported by the mean annual flood.
Formation of an armoring layer on the bed is unlikely since coarse, nontransportable particle
sizes are missing from the distribution.