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While we are developing high resolution SGS output in the future release to address this issue, we have also added a new functionality in the [[ASC_to_ASC|ASC_to_ASC]] utility to 'remap' a water level grid to a finer DEM grid. This page introduce how to use the [[ASC_to_ASC|ASC_to_ASC]] remap function, and also discuss the limitation of the method.
=Remap Water Level to Finer DEM=
=Base Case=
<tt>asc_to_asc.exe -remap -wl lowres_h.asc -dem DEM_highres.asc</tt><br>
A simple 1D/2D model has been constructed based on [[Tutorial Module02|Tutorial Module 2]]. SX points have been used to connect a 1D culvert (FC01.2) with the 2D domain. The culvert details are: <br>
In this command:<br>
* Type = R (Rectangular)
'''"-wl <wl_file>"'''<br>
* Number of barrels = 5
Sets the coarser resolution water level grid to remap from.<br>
* Width per culvert = 2.4m (i.e. the total width of the bank of culverts is 12m)
'''"-dem <dem_file>"'''<br>
* Height = 1.2m
The figure below overlays the remapped water depth on top of the 10/20m model water level output, and compared it to the original water depth output.<br>
Three 2D cell resolutions have been tested: 5m, 2m and 1m. The figure below shows the 1D/2D linking cells of the culvert.<br>
Sets the finer resolution DEM.<br>
[[File:1D2D_Model_Stability_001.png|500px]]<br>
The default interpolation method is TIN. But "-idw_npt<number of points>" flag can be used to change the interpolation method to IDW and set the number of points used for IDW interpolation (default is 12).<br>
Example:<br>
This figure highlights the variation in 2D storage volume associated with the 1D/2D SX connections. The storage associated with a single 1D/2D linking cell for each cell size is:
<li>
* 5m 2D cell size = 25m<sup>2</sup>/m
* 2m 2D cell size = 4m<sup>2</sup>/m
* 1m 2D cell size = 1m<sup>2</sup>/m <br>
The modelled flow rates in the culvert are presented in the figure below.<br>
[[File:1D2D_Model_Stability_002.png|500px]]<br>
Two key observations can be made:<br>
* The 1D/2D link associated with the 1m 2D cell size is not stable.
* The flow rate results through the 1D culvert decrease with cell size. This is an issue. It indicates cell size convergence (i.e. consistent results independent of cell size) was not achieved. This is caused by the 2D storage volume associated with the 1D/2D connection being insufficient compared to the flow area associated with the 1D channel (12m width). As a result, the 2D boundary cell is the model feature limiting flow exchange between the 1D and 2D, rather than the dimension and hydraulics associated with the 1D structure.
''Please note that a culvert connection to a single 2D cell is provided here as an example. Connections with a 2D cell width less than the structure face width is not recommended. For example, a 12m wide set of culverts should be connected to at least 12 x 1m cells, 6 x 2m cells and 3 x 5m cells respectively. Examples how this can be done are shown in the following sections.'' <br>
=1D Timestep=
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