The dispersion coefficient, D, is used for both the Advection-Dispersion and the Sediment Transport modules. It is described as a function of the mean flow velocity, V, as shown below.
Where ‘a’ is the dispersion factor and ‘b’ the dispersion exponent. Typical value ranges for D: 1-5 m2/s (for small streams), 5-20 m2/s (for rivers).
Both the ‘dispersion factor’ and the ‘dispersion exponent’ can be specified. If the dispersion exponent is zero then the dispersion coefficient D becomes constant (equal to the dispersion factor). By default the dispersion is zero (i.e. there is only advective transport and no dispersion).
The ‘Minimum dispersion coefficient’ and the ‘Maximum dispersion coefficient’ parameters are used to control the range of the calculated dispersion coefficients.
Global dispersion values are defined in this group. Global values are defined in all branches and calculation points unless Local values are defined additionally.
Dispersion factor
The dispersion factor equivalent to parameter a in equation (9.2) is defined here.
Exponent
The dispersion exponent equivalent to parameter b in equation (9.2) is defined here.
Minimum disp. coefficient
Using equation (9.2), the dispersion coefficient value is depending on the velocity that vary during the simulation. This parameter defines the lowest allowed value of the dispersion coefficient during simulation.
Maximum disp. coefficient
Using equation (9.2), the dispersion coefficient value is depending on the velocity that vary during the simulation. This parameter defines the highest allowed value of the dispersion coefficient during simulation.
MIKE HYDRO uses the values specified under global values except for those locations were local values have been specified. To add or remove these locations to the table use the Append and Delete buttons (‘+’ or ‘-’): When a local value item is included, a line is added to the local values table, where the following specification must be defined:
Branch Name
Name of the river branch with local dispersion values.
Chainage
Chainage in river with local dispersion values.
Dispersion factor
Local value of the dispersion factor.
Exponent
Local value of the dispersion exponent.
Minimum coef.
Minimum value of the dispersion coefficient at the location.
Maximum coef.
Maximum value of the dispersion coefficient at the location.
The advection-dispersion properties at a given location can be displayed in the Property View if the checkbox of the specific row in the table is checked. When several table items are checked, it is possible to unselect all of them at the same time by clicking on the “Clear selection” button (‘x’).
