9493

• UCREFRP Catalog Number: 9493
• Author: Gaeuman, D., P. R. Wilcock and J. C. Schmidt.
• Title: High Flow Requirements for Channel and Habitat Maintenance of the Lower Duchesne River between Randlett and Ouray, Utah.
• USFW Year: 2003.
• USFW - Doc Type: \
• Copyright Material: NO

FINAL REPORT, November 2003
High-flow Requirements for the Duchesne River

error, such that gross volumetric uncertainty for any individual polygon (bVg) was estimated as
the square root of the sum of squared contributing errors and uncertainties:

8Vg = ~&a: +(A.8HY

(5)

where A is the area of erosion or deposition. Gross volumetric uncertainties for erosion volumes
( 8 Vgl ) within each channel subdivision, i, were found by summing bVg for all erosion polygons

in each subdivision, i. Gross volumetric uncertainties for deposition volumes ( 8 V~ ) were

similarly found by summing bVg for all depositions polygons in each subdivision. Gross
volumes are reported as a percent of the measured erosion or deposition in each subreach (Table

7).

Uncertainty in Estimated Changes in Gravel Storage
Uncertainty in estimated changes in gravel storage is produced primarily by uncertainty in
the thickness of gravel in the alluvial deposits. Planimetric errors are considered to have little
effect on the calculation of changes in gravel storage (Ham and Church 2000). A local positional
error that produces a false erosion polygon on one river bank also produces a false deposition
polygon on the opposite bank, even in the absence of real channel movement. The magnitudes
of total local erosion errors and local deposition errors are similar, so that net differences
between the reported areas of erosion and deposition not affected by the planimetric error.
Equation 5 then reduces to:

8V=A.8H

(6)

where bV is the uncertainty in the volume of erosion of deposition in a specific polygon.
Uncertainty regarding gravel deposit thicknesses exists independently for the eroded .
sediments and for the deposited sediments. Both sources of uncertainty must be considered
when evaluating changes in gravel storage. The total uncertainty for estimated storage changes
on the scale of channel subreach (Table 7) is then the combined uncertainties associated with the
estimated volumes of erosion and deposition:

8 D.Si = ~(8V; Y + (8V/y

(7)

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