PERMFILE109309

• Permit No: M2001001
• IBM Index Class Name: Permit File
• Doc Name: EXHIBITS FOR MLRB HEARING
• Section_Exhibit Name: EXHIBIT F #3 05/23/01
• Media Type: D
• Archive: No

100
90
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• ~ Sediment in Channels 201
1
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8 ~4 2
J ~ O 7 Diameter of padicles (mm)
Fine sand i Metlium Coarse
Sand f sand Very Granules
coarse sand Pebbles
7

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I Erosion (and transpcdalion) I / ~ f-
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195=; Ashworth and Fur4uson 1969). In (act, some in-
vrstigators argue that these particle-hiding effects are
su si;;niticant that the critical shear stress required to
untraln a particle increases only slightly; if at all, with
its diameter, a concept rcterred to as the tquol rnnhilihf
hgputh<~i: (Parker et al. 19S2; Andrews ]963; Andrews
and Erman 1966; \Vilcock and Southard 1955).
.\shwurth and Ferguson (1969) point out, however,
that if precise equal mobility held for the entire length
uE a channel, the dow•nstruam particle fining observai
along many ricers could occur only through abrasion
dunng transport or tvcathering during periods uE rest,
but this hypothesis is inconsistent with must studies of
dnt~~nstrram particle roduc[ion (Ashworth and
Fri;{uson 195N; N'rrrith~ 199?). In addition, [hc notion
uE ryual nutbility runs nattran• to a host of studies that
hoer ilcdrlP shoran drat selective entrainment occurs;
that i;, lar~ar partidas arr rntnined as shear strui in-
FIGURE 6.9
Portion of Hjulstrbm curve with size
grades B to H placed on diagram.
Compare figures 6.7 and 6.8.
(Rube/ 19391
creases. Thus, true equal mobility is probably not p~s-
sible except, perhaps, under extreme flood conditions
(Ashworth and Ferguson 1959; Komarand Shih 1993..
Nevertheless, there is little doubt that sediment char-
acteristics including sorting, layering, and particic•
shape and orientation intluence initial grain motion.
(Carling et al. 1992; Kumar and Zhenlin 1955; Koma:
and Shih ]992).
Bank Erosion
The processes uE entrainment determine the type
and magnitude of erosion that occurs on the chmutc~i
floor. It is incorrect, though, to assume that the urf.
significant erosion is vertically directed. Bank erosive.
tchich proceeds laterally, not onh• cuntributrs to'tL••_
sedimentary load but also, through its control nn char-.-
nrl taidth, everts a direct intlurnce on other channt: