FLOOD06421

• County: Statewide
• Basin: Statewide
• Title: Highways in the River Environment
• Date: 2/1/1990
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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D
50

= sediment riprap size for which 50% by weight of the particles are

smaller; similarily D ,D ,D represent sizes for which 65, 84,
65 84 90
and 90% of the particles are smaller

= mean sediment size a distance x downstream from reference location

D
50
X

D
50
o

= mean sediment size at the reference section

D = effective mean diameter of sediment or riprap
m
D = sediment size or riprap size
s
dA = differential area for the fluid entering the control volume
1
dA = differential area for the fluid leaving the control volume
2
d = thickness of riprap layer
rr
ds = displacement of a fluid particle during time dt
d = scour depth
s
dt = differential time interval
E = energy of a system
E = ratio of bed layer thickness to flow depth a/y
o

e

= energy per un it mass

e ,e I
1 2
e ,e = moment arms; of forces acting on a rock particle
3 4
e = eccentricity coefficient
c
F ,F = pressure force acting at section one and two
1 2
F (n), F (n) = functions for the transverse velocity distribution in bends
1 2
r B = buoyant force on a particle
r b = force exerted at the boundary
r = critical Froude number for the beginning of motion of sediment
c
r D = drag force on a particle
r d = drag force on a rock particle
r f = fluid force on a particle
r = gravitational force on a particle
g
r i = Ii ft force on a rock particle
F = external forces between particles
n
Fr = Froude number

r
s
r
v
r
x

= shear force
= shear force on a particle
= force acting in the x direction

xxxi