WSP06982

• File Number: 8220.101.10
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powel-Glen Canyon Adaptive Management
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2003
• Author: Melis-Topping
• Title: Testing Laser-Based Sensors for Continuous In Situ Monitoring of Suspended Sediment in the Colorado River Arizona
• Water Supply Pro - Doc Type: Report/Study

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Fi~. I Map of the Colorado RI....er downstream from Gkn Canyon Dam

environmental management. One major objective of the monitoring programme is to
identify key periods when the ecosystem's sand supply is sufficiently enriched for
artificial floods to rebuild sand bars. Typically, this is done by estimating the system-
wide sand mass balance between influx from tributaries and export from Grand
Canyon. Daily measurements of suspended transport using isokinetic samplers from
cableways are currently required to estimate monthly-ta-seasonal sand flux below the
dam. Collection of these samples is logistically complicated. costly, and provides
limited spalial and temporal resolution with respect 10 the variability of sand transport.
The objcctive of this paper is to evaluate the potential for using L1SST technology to
increase the spatial and temporal resolution of suspended-transport monitoring in the
Colorado River.

RESULTS ANIlIlISCUSSIO:\

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Initial point data collected at a fixed-depth, near-shore site were obtained by averaging
16 measurements al 2.min intervals during a 24-h deployment starting at 23:00 h GMT
on 19 July. 2001. These data were collected using a L1SST-lOO "Type-B" sensor
(baser In.~itu .s:caltering and Iransmissometry) mdllllfactured by ISequoia Scientific.
Inc. in BeHevue. Washington. USA. The Type-B is a laser-diffraction based sensor
designed to detect suspended particles over a size range of 1.3-250 11m. An additional
descnption of this technology is reported by Agrawal & Pottsmlth (2001). The L1SST.
100B used in July 2001, ~'as previously evaluated under laboratory and tield
conditions and its performance is reported by Gartner ('1 al. (2001).
The 720 L1SST pomt measurements collected at the Grand Canyon gauge in July
2001. compare well with cross-sectional integrated suspended-sand and silt & clay
data collected at a cableway near the test site using a D-77 isokinetic b."lg sampler (Fig.
2). During the July 200 1 test. lluctuatmg releases from Glen Canyon Dam ranged from
about 32Q---480 mJ S.1 (typical diurnal pattern of discharge related to hydropower
generation .11 the dam). In addition to accurately trackmg the sand concentration. the
L1SST.IOOB also recorded the physically-expected increase in sand-concentration
\'ariance as llow increased. With peak values ranging from 50 to 140 mg 1"1 (Fig. 2(a)).
Concentrations of silt and clay obtained by the L1SST-IOOB were a raclor of nine less