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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Test/nx Ia.~er-bast'd senwn for continUOUS In SIlU monilorHlg o[suv-.ended .w'd,menl 5

-lISST2S8POiI\lT I.lEASUREII.IENT (NO C....1.I8AATION)
o CROSS-SECTlONAU. Y I,..TEGAATEO WITH o..n SAMPLER
-OISCHARGEOI' WATER

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Fig. 5 Comparison of local ML~pended+sediment concenlrallons (1.3-250 j.Im)
measured allhe Grand Canyon gauge using L1SST-25 and [)..77 bag ~mp[er during
the mulli.....eek fall 2001 lest. DlliCharge dala are from the Gr.md Canyon gauge.

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L1SST-25 provided the most compelling results as to how well these optical
Instruments perform during continuous deployments (Fig. 5). Even during September
200t. when the LlSST-25 was technically oUl-of-rnnge (laser transmission <2(010),
these non-calibrdted data generally tracked the 0-77 samples.
Although the non-calibrated test results from the LlSST -25 compare well with
cross-section measurements for total concentration (once the volume to mass
conversion was made, Fig. 5). the LlSST-25 provides no possibility for separating
measurements of sand from finer panicles (the sand split is made at 63 11m). This
L1SST -25 limitation presents a serious shortcoming for monitoring deploymt'nts where
sand transpon is of primary concern. such as the Colorado River. During the 2002 field
tests, the manufacturer developed a L1SST -25 lirnlware upgrade to segregate sand
from liner-panicle data and made it available for testing (L25X). The July 2002 sand
concentrations derived from the L25X compared very well with cableway sample data
(R' = 0.86).
During relatively brief periods when the river below the da.m becomes greatly
enriched with tine sediment from tributary inputs, LlSST overestimates the
concentration of flOe panicles (Fig. 5). Such errors occur owing to multiple scallenng
associated with abundant fines. a phenomenon that tends to bias counts on the outt'r
rings of the detector array. Multiple scallenng has been identified as a significant
source of concentration error when laser transmission falls below 20% (Agrawal &
POllsmith. 2001). To monitor such periods. a method was devised that allowed the
L1SST to electronically control a programmable automated pumping sampler. The
protocol is as follows: when L1SST measures laser transmission below the 20~.o