FMA Challenge 1 (1D-2D linked): Difference between revisions
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==Use of Scenarios to Modify 2d Grid Resolution==
A 15ft (~4.5m) 2D grid resolution is extensively used for urban modelling, and in this case provides a good trade-off between resolution and run time. 15ft cells are small enough that flow paths down roads are adequately represented (provided the DEM accurately represents the roads as discussed above).▼
To test the effect of different resolutions, simulations were made using grid resolutions of 5, 10, 15, 20 and 40 ft (Noted that only the 10 and 15ft are presented in this example).
To run the model with varying cell sizes from a single TCF, the use of scenarios has been implemented. The scenario here either '10ft' or '15ft' can be entered in the batch file using the -s command. If the -s command is not used, the model will assume a default model scenario of 10ft as specified by the line <font color="blue"><tt>Model Scenario </tt></font> <font color="red"><tt>==</tt></font> <tt> 10ft </tt> within the TCF.
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The cell size, 2D timestep and log output frequency are all set externally using a read file called from the TCF: <font color="blue"><tt>Read File </tt></font> <font color="red"><tt>==</tt></font> <tt> FMA_T1_CellSize_Commands_001.trd </tt><br>
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*Within the TGC, <<2D_CELL_SIZE>> is replaced with 10.
▲A 15ft (~4.5m) 2D grid resolution is extensively used for urban modelling, and in this case provides a good trade-off between resolution and run time. 15ft cells are small enough that flow paths down roads are adequately represented (provided the DEM accurately represents
Upon examination of the results, the flood extents varied by unexpected amounts between different resolutions. For example, the 10ft grid scenario (provided as part of the ftp download) produces a more extensive flood extent, even though the profile down the 1D channel is almost identical to the 15ft case. The extended flooding is the result of very shallow flow (less than 0.01ft deep) over large flat (horizontal) areas caused by the use of contours to create the DEM as discussed above. Due to the slightly coarser resolution the 15ft grid does not let water on to some of these flats, and they remain dry. Should an accurate DEM be made available for this Challenge, the flood extents are likely to be very different and much more consistent between different grid resolutions!
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