Model help:FallVelocity

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The CSDMS Help System


This model is used to calculate Particle fall velocity.

Model introduction

This model calculate fall velocity for spheres. Uses formulation of Dietrich (1982).

Model parameters

Parameter Description Unit
Input directory path to input files
Site prefix Site prefix for Input/Output files
Case prefix Case prefix for Input/Output files
Parameter Description Unit
kinematic viscosity of water (ν) m2 / s
Submerged specific gravity of sediment (R) -
Grain size (D) mm
Acceleration due to gravity (g) -
Parameter Description Unit
Model name name of the model -
Author name name of the model author -

Uses ports

This will be something that the CSDMS facility will add

Provides ports

This will be something that the CSDMS facility will add

Main equations

  • Explicit particle Reynolds number
[math]\displaystyle{ Re_{p} = {\frac{\sqrt { R g D } D}{\nu}} }[/math] (1)
  • Dimensionless fall velocity
[math]\displaystyle{ R_{f} = exp \left ( -b_{1} + b_{2} ln \left ( Re_{p} \right ) - b_{3} \left ( ln \left ( Re_{p} \right ) \right ) ^2 - b_{4} \left ( ln \left ( Re_{p} \right ) \right ) ^3 + b_{5} \left ( ln \left ( Re_{p} \right ) \right ) ^4 \right ) }[/math] (2)
  • fall velocity
[math]\displaystyle{ R_{f} = {\frac{v_{s}}{\sqrt { R g D }}} }[/math] (3)


b1, b2, b3, b4, b5 are all parameters from Dietrich(1982).

This formulation is only valid for Reynold’s numbers less than or equal to 2.5·106. If Rep is greater than this upper limit, the function will alert the user, and exit the program.


An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations:

See also: Help:Images or Help:Movies


Gary Parker


Dietrich, E. W., 1982, Settling velocity of natural particles, Water Resources Research, 18 (6), 1626-1982.