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<tt>asc_to_asc.exe -remap -wl lowres_h.asc -dem DEM_highres.asc lowers_hazard.asc</tt>
This command reads in an extra grid 'lowers_hazard.asc' and remaps it to the finder DEM resolution.The figure below compares the original hazard output from the 10/20m SGS model and the remapped hazard output.<br>
[[File:Fig5 D sgs remap zoom.png|700px]]<br> ▼'''Figure 5 Remapped vs original water depth for 10/20m mesh SGS model.'''<br><br>
overlays the remapped water depth on top of the 10/20m model water level output, and compared it to the original water depth output. As can be seen, smooth water depth along the gully and flood fringes is produced by the post process utility.<br>
[[File:fig7 ZAEM1 sgs.png|700px]]<br>
'''Figure 7 Remapped vs original water depth for 10/20m mesh SGS model.'''<br><br>
It is important to note that, for output types other than depth, this utility does NOT interpolate the result from the coarser grid to the finer grid, but only extended/reduced the output extent to the dry/wet extent. Therefore, the resolution of the remapped hazard above remains the same as the original output grid. The interpolation is not conducted for the following reasons:
[[File:SGS 02-20m ZAEM1.png|700px]]<br>
* Hazard categories are usually depended on both water depth and velocity, and it is not straight forward to interpolate a cell averaged velocity to sub-cell scale with varying water depth.
'''Figure 8 Remapped vs original water depth for 10/20m mesh SGS model.'''<br><br>
* Even if this can be done based on empirical relationship between depth and velocity, the obtained velocity is much less reliable than a actual output from a model with finer mesh.
write (*, '(" The values of lowers_hazard.asc are refined and extended/reduced to the dry/wet extent")')
Therefore, we highly recommend refining the mesh size directly a the location where user wants to obtain finer velocity or hazard output. The figure below shows the hazard output from the 2.5/5/10/20m model, and as can be seen the result is much smoother along the gully.
write (*, '(" of the high resolution water depth remapping result. Note that no interpolation is applied
▲[[File: Fig5SGS D02-20m sgs remap zoomZAEM1.png| 700px350px]]<br>
Selection of a 1D timestep that is too large can cause instability. The TUFLOW manual includes some discussion on 1D timestep selection and courant number criterion. Conceptually a 1D timestep should be chosen to ensure a volume of water does not travel a distance longer than the shortest 1D channel within a model. For example, if the flow velocity and celerity is 5m/s and the 1D channel length is 10 metres, the 1D timestep should be less than 2 seconds. To provide some tolerance for faster flows associated with different flood events, a timestep of 1 second may be appropriate.
During real world studies it is good practice to check the 1D timestep sensitivity: <br>
* Select a 1D timestep based on the smallest channel length and the expected flow velocity within your model. <br>
* Trial using a smaller 1D timestep to establish whether the problem is timestep related. <br>
If the instability is not timestep related, reducing the timestep should have a negligible change in results. <br>
A 1s 1D timestep has been used for this testing. It is appropriate for the 1D features being modelled.<br>
''Note: The 1D timestep for a HPC 1D/2D linked model is the 'limiting' timestep the 1D solver can use. The 1D solver has been reconfigured to act as an adaptive/varying timestep solution, and the 1D timesteps are set at different multiple of 2D timesteps. <br>''
=1D/2D SX Links Defined Using 1D Nodes (1d_nwk) =
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