6.2. Prepare Data
6.2.1. Coefficient of friction
The plugin will export the roughness according to these priorities:
If
reach.coefficient_of_friction
is set then it is converted (1/coefficient_of_friction
) and exported to SWMMElse if
reach.wall_roughness
andreach.clear_height
are set, it is converted ((1/(4 * SQRT(9.81)*POWER((32/re.clear_height/1000),(1/6))*LOG(((3.71*re.clear_height/1000)/(re.wall_roughness/1000)))))
) and exported.Else if
reach.swmm_default_coefficient_of_friction
is set then it is usedElse a default value of
0.01
is setSee
vw_swmm_conduites.sql
for details
Bemerkung
The formula to convert from Strickler to Coolebrook is documented in *ATV-DVWK STANDARD ATV-DVWK-A 110E, Hydraulic Dimensioning and Performance Verification of Sewers and Drains September 2001*
6.2.1.1. Populate default coefficient of friction
The table tww_swmm.reach_coefficient_of_friction
contains default coefficient of Strickler for the reach materials.
The file ../project/qml/reach_coefficient_of_friction.qml
is the layer definition, that you can import in your QGIS project.
If the default values don’t match your needs you can edit them.
The function SWMM Set default coefficient of friction
will put in tww_od.reach.swmm_default_coefficient_of_friction
these default values.
You can choose if you want to overwrite or not the values existing in this attribute.
Launch SWMM Set default coefficient of friction
:
Overwrite existing default values
: If checked the values stored inswmm_default_coefficient_of_friction
will be overwrited with new values.