Encyclopedia of Environmental Science and Engineering, Volume I and II

SEDIMENT TRANSPORT AND EROSION 1075

fd=^8 (40)

v  16 R^2 
^3 S^1 
^3 (41)

PQ=267. (42)

in which R  hydraulic radius (ft.); d  medium grain diam-

eter (inches); P  wetted perimeter (ft.) Q  dominant dis-

charge  PR (cfs.).

The dominant discharge in the case of canal flow is the

design flow. In the case of a natural stream it is the channel

forming flow which is often taken to be the bankfull dis-

charge^3 which has an approximate return period of, between

1.25 and 2.33, years.

Blench^43 advanced the work of Lacey and introduced

bed and side factors to better describe the depth and width of

a channel in regime. His equations are:

f b  v^2 
 y  bed factor (43)

f s  v^3 
 b  side factor (44)

and

S

ff

gQ c

= bs

+

() ()

.(/)

,

///

/

56 112 14

16

1

3 63 1 2330

(45)

in which c is the concentration in ppm; b  mean width

(ft—sec. units). The recommended f b is

fdb=+9 6 in 1 0 012.()(. )c (46)

1 2 4 6 1.0 2 4 6 1.0 2 4 6 1.0 2 4 6 1.0

MEAN VELOCITY ft/sec

0.1

1

10

100

1000

10,000

DISCHARGE OF SANDS, tons/day/foot of width

DEPTH

0.1 ft

DEPTH

1.0 ft

DEPTH

10 ft

DEPTH

100 ft

Sand Size

0.1 m.m.

0.2

0.4

0.8

FIGURE 12 Sand discharge (after Colby).

C019_001_r03.indd 1075C019_001_r03.indd 1075 11/18/2005 11:06:01 AM11/18/2005 11:06:01 AM