8252

• UCREFRP Catalog Number: 8252
• Author: Allred, T. M. and J. C. Schmidt.
• Title: Channel Narrowing of the Green River Near Green River, Utah
• USFW Year: 1999.
• USFW - Doc Type: History, Rates, and Processes of Narrowing.
• Copyright Material: NO

21

The Rate and Process of
Vertical Accretion

Discharge measurement data were used to reconstruct the formation of

the inset right bank near the present cableway. Cross sections were plotted for

those times when the right bank was inundated, and these data provide a

detailed picture of the rate of vertical accretion for this deposit (Fig. 16b). Little

accretion occurred between 1965 and 1983 because the deposit was rarely

inundated. Ground surface in 1965 and 1973 was determined from the cross-:

section notes and corresponds to the two organic layers exposed in the trench.

The elevation determined for each time was the average for the nearly

horizontal surface at the right bank (Fig. 16b). These data show that accretion

rapidly occurred on the bank-attached bar between 1957 and 1965.

The trend in the rate of vertical accretion shown in Figure 16a is

consistent with Wolman and Leopold's (1957) conceptual.diagram, although the

rates of accretion are different. The gray areas on Fig. 16a indicate periods of

inundation and are the only possible periods of deposition. Figure 16 also

illustrates that large magnitude floods of rarer recurrence can lead to episodes

of rapid deposition, as seen in the 1983 flood. Accretion is episodic, and the

smooth curve of Wolman and Leopold (1957) disguises the incremental nature

of inundation and subaerial exposure, and masks the variable nature of
overbank deposition.