7780

• UCREFRP Catalog Number: 7780
• Author: Brooks, J. E., et al.
• Title: San Juan River Seven Year Research Program Summary Report 1992.
• USFW Year: 1992.
• USFW - Doc Type: \
• Copyright Material: NO

prepared for the San Juan River from Navaj o Dam to Lake Powell .
This base map was developed from USGS quadrangle data at 1:24000
scale with river channel alignment taken from 1986 and 1988 aerial
photography. The digitized data form the basis for geo-referencing
field data and for the graphical information system (GIS) being
developed to store, analyze and present data.
One 4 RM reach (RM 133.5 to RM 129.5) was mapped at 1:2400 with 0.3
m (1.0 ft) contour intervals. The digital base map for this reach
will be used for geo-referencing detailed habitat mapping. The
1992 aerial photographs used to develop the base map will be used
for field mapping.
Geomorphic Characterization - The San Juan River was characterized
by data analysis in four broad areas; (1) channel bed slope, (2)
channel pattern, (3) instream channel features, and (4) cross-
section form. The goal was to identify similar geomorphic reaches
that would allow subsampling and extrapolation to the whole.
Bedrock geology in the area is important in locally restricting
lateral movement, but rarely controls bed elevation from Navajo
Reservoir to Bluff (RM 68). In this reach, channel bed elevation
is mainly controlled by cobble and gravel of Pleistocene origin.
Below RM 68, the channel is primarily bedrock controlled.
The San Juan River gradient is moderately uniform when considering
long reaches (> 20 km). The average gradient of typical reaches
varies from about .0014 to .0021, with a mean of about .0015.
Locally, the slope varies greatly as the river passes over cobble
or bedrock control, resulting in flatter reaches separated by steep
short reaches.
Three mile running average channel sinuosity was calculated for the
study reach. The data indicate that in the lower reaches of the
study-area (RM 52 to RM 70), the river sinuosities were highest,
reaching a maximum of 5.0 and a minimum of 1.2. The sinuosity in
this reach is canyon induced rather than an indication of meander
within a river basin. Throughout the remainder of the study area,
the sinuosity varied greatly with ranges from 1.0 to 1.7 and an
average of about 1.2. There are four locations of markedly
increased sinuosity upstream of RM 70. The areas occur just below
Navajo Dam at RM 208, at about RM 176, RM 140 and RM 121.
There are two areas of extensive braiding (RM 140 to RM 130 and RM
160 to RM 150) with minor areas at RM 190 and RM 185. The
remaining areas had only limited island formation and braiding
activity., These data are consistent with the surface areas of
secondary channels as mapped by the USBR studies.
The Remote Sensing and Geographic Information Section of
Reclamation reported instream channel features at a flow rate of
128 m3/sec (4,530 cfs) and these data were included in the
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