The dredge option allows for simulated dredging of any part of the model, either at a specified rate or to a given level. The start and completion times of the dredging operations are variable. To activate dredging, include a block with the dredging details in the sediment datafile (.sed). This option can be specified anywhere after the General System Parameters. Overall, Flood Modeller allows three methods to update cross-section bed. For more details, refer to the Method for updating cross section shape.
Method 1:
No changes are required in the cross-section datafile.
Dredging is applied uniformly across the entire section.
When dredging to a level, the specified level is the minimum elevation in the section.
Methods 2 and 3:
‘DREDGE’ markers must be placed in the cross-section data to define the lateral limits of dredging.
A pair of ‘DREDGE’ markers is added to any cross-section, with the first marker defining the left extreme and the second marker defining the right extreme (See example figure below)
Cross-section points at and between the ‘DREDGE’ markers will be lowered during the simulation.
The 'DREDGE' markers should not be placed at the extreme edges of a section, especially when dredging to a level is specified. Otherwise dredging will result in the channel shape being lost altogether and a horizontal bed at the dredged level will be produced.
Dredging can be specified for cross sections at upstream boundaries or immediately downstream from junctions or structures. Dredging at these locations will affect the cross-section shape and the flow predictions, but it will not affect the sediment balance due to the algorithm used to relate sediment loads with bed level changes (see under 'Sediment continuity equation' earlier in the manual). An example of the structure of this section of the dredging block, starting with the keyword 'DREDGE', is shown in the figure below.
A sample sediment datafile with Dredge option is attached here for help.
Datafile Format - Dredge Option
Line 1 keyword 'DREDGE'
Line 2 n1, itype, [tm]
Line 2 labeli, start_time, end_time, itype_value
Where
n1 = number of ensuing node labels
itype = integer defining the method of dredging. Enter one of the following:
1 dredge to constant level
2 dredge at constant rate
tm = optional keyword or value for units of time in following data set. Can be any numerical multiplier or one of the following: seconds (default), minutes, hours, days, weeks, months (30 days) or years.
labeli= node labels of dredged sections
start_time= start time of dredging in units of tm
end_time= end time of dredging in units of tm
itype_value= if itype = 1, required bed level in m
if itype = 2, dredge rate in m/time (in units of tm)