Sediment Properties

If reservoir sedimentation is included in Basin Modules the following Sedi­ment properties must be defined:

·         Density

·         Porosity

·         Settling velocities

Density is assumed equal for all sediment types. By default the model uses a density of 2650 kg/m3, which is the density for quartz.

Porosity (the volume of pore-space in sediment) is assumed equal for all sed­iment types. By default the model uses a porosity of 0.4 which is the typical porosity of naturally deposited, non-cohesive sediments.

The sediment can be defined by one or more grain size classes in the table. Each grain size class must be assigned a settling velocity. To add a sediment grain size class click the ‘+’ in the tool bar above the sediment class table and specify the associated settling velocity.

Table 12.1 shows some average settling velocities for various grain sizes

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Table 12.1          Sieved diameter ds, Spherical diameter dv, fall (or sedimentation) diam­eter df and associated settling velocities w in water with a temperature of 10ºC and 20ºC.Source: Engelund & Hansen, 1972: ‘A monograph on sediment transport in alluvial streams’

ds (mm)

dv (mm)

df (mm)

w (10ºC) (m/sec)

w (20ºC) (m/sec)

0.089

0.10

0.10

0.005

0.007

0.126

0.14

0.14

0.010

0.013

0.147

0.17

0.16

0.013

0.016

0.208

0.22

0.22

0.023

0.028

0.25

0.25

0.25

0.028

0.033

0.29

0.30

0.29

0.033

0.039

0.42

0.46

0.40

0.050

0.058

0.59

0.64

0.55

0.077

0.084

0.76

0.80

0.70

0.10

0.11

1.25

1.4

1.0

0.15

0.16

1.8

1.9

1.2

0.17

0.17

 

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Note that the sediment properties are global values used throughout the entire model. It is not possible to make spatial variation of definitions for sedi­ment fraction properties.