FLOOD00867

• County: Statewide
• Title: Determination of Channel Change for Selected Streams, Maricopa County, Arizona
• Date: 1/1/2002
• Prepared For: Maricopa County Arizona
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

Table 1. Channel properties at selected streams, Maricopa County, Arizona-Continued
Cross- Channel properties
section Change In
number and Dale Reference Width, in area from Change in area,
(or) elevation, in Hydraulic Area, in initial survey, In percent
feet radius, In feet square feet
local Ion feel In square feet
09517280 Tiger Wash near Agulia, Arizona
08-1 s-{)5 8 113 3.0 338
01HJ1-70 8 123 2.3 287 -51 -15
09-19--72 8 120 2.2 270 -68 -20
06-20-95 8 118 3.3 396 58 17
08-10-97 8 120 3.3 401 63 19
lo-D9--97 8 117 3.9 469 131 39
09510000 Verde River below Bartlett Dam, Arizona
01--04-93 7.5 195 4.9 965
01-19-93 7.5 190 4.2 804 -161 -17
01-21-93 7.5 175 4.5 749 -216 -22
02-15-95 7.5 151 5.7 873 -92 -10
04-28-95 7.5 140 4.4 617 -348 36
09514200 Waterman Wash near Buckeye" Arizona
09-16-64 5 192 2.3 448
09-16-66 5 174 2.8 484 36 8
11-11-71 5 190 1.7 330 -118 -26
lo-D5-82 5 169 1.2 205 -243 -54
11-30-96 5 162 1.7 283 -165 -37
08-14-97 5 171 2.0 342 -106 -24

To provide a datum for measuring channel
geometry at a cross section, a reference elevation
was established at each site for this study. The
amount of change at a cross section was calculated
relative to its reference elevation. The reference
elevation for each cross section was high enough
to include the area of the greatest scour and fill but
low enough to eliminate large areas of the cross
section that may experience no scour or fill, such
as at the edges of the flood plain. Given that the
deepest and fastest sections of any cross section
usually convey the most flow, use of the reference
elevation emphasizes channel change in the main
channel only. This methodology allows for the
comparison of the channel geometry determined
from current-meter measurements with that from
channel surveys. Because the reference elevation
remains constant between measurements, changes
in channel geometry are the result of channel scour
and fill only, but only represent a small portion of
the cross section during flood flows. Cross-section
measurement date, reference elevation, hydraulic
radius, width, and cross-sectional area are given
for each site (table I). The change and percent

change in cross-sectional area were computed on
the basis of data for the first measured cross
section (table 1). A positive change in cross-
sectional area represents scour or an increase in
cross-sectional area, and a negative change re-
presents fill or a decrease in cross-sectional area
compared with the first measured cross section.

Point-of-Zero-Flow Method

As a part of routine discharge measurements
and gaging-station inspections, hydrographers
often determine the PZF. The PZF is the gage
height at which flow begins. The PZF can be
highly variable in sand channels because the
control for the gaging station can shift as a result
of low flows. In this study, the PZF was used to
represent the channel elevation. Although the PZF
is not an exact representation of a channel-bed
elevation, it does show fluctuations in channel
elevations through time and the relation of the
channel-bed elevation to floods.

Methods of Determination of Channel Changes 7