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Table of equations, mainly for
rivers.
Basic |
|
|
Force balance |
SF = 0, or SF = ma |
The second form is used if there are any accelerations |
Hydro or litho static pressure |
P = r g d |
r is the material density, and d is the depth of burial |
Shear and normal stress in a fluid |
|
|
Shear stress, parallel to slope at some depth (depth perpendicular to slope, but often just the vertical depth is used.) |
t = rgd sina |
See notes on slope angles and depths |
Normal stress, perpendicular to slope |
s = rgd cosa |
|
Reynolds number |
Re = r v d / m |
Where v is a flow
direction velocity and d is a cross stream dimension |
Froude number |
Fr =
v / ( g d )1/2 |
|
Stoke’s setting velocity |
w = (rs - rf) g D2 / ( 18 m ) |
|
Shear velocity |
U* = ( tb / rf)1/2 |
|
Bernoulli pressure/velocity |
DPw = - (Dv)2
/2 |
|
Shield’s parameter |
Q
= tb / (rs - rf) g D |
This equation can be
inverted to get the critical shear stress tc to get
a particle moving |
Mannings equation |
V = R2/3 S1/2 / n |
R is the cross-section
area divided by the wetted perimeter, S is slope and n is tabulated, this
equation is written for MKS units only |
Chezy eqn. |
V = C R1/2 S1/2 |
|
MPM equation for sediment load |
qs = A (tb - tc) 3/2 |
Bedload or total load per
unit width of channel |
Super-elevation in meander bends |
Dz = v2 w / (gR) |
W is the channel width,
and R is the bend radius |
Alluvial diffusion equation |
|
If the second term is ignored, this is
just the simple diffusion equation, and can be thought of in terms of
behavior just like the rainsplash equation |
Bedrock kinematic equation |
|
This is a kinematic wave
equation with velocity Eqw. |