TUFLOW Output Discussion: Difference between revisions
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== How do I apply high resolution (HR) output and what are the options? ==
See the <u>[[TUFLOW_HR_Output | TUFLOW HR Output]]</u> Wiki page for details.<br>
== Why are there differences between high resolution grid from TUFLOW and remapped outputs generated by the asc_to_asc utility? ==
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Water level outputs, however, assume that water fills from the bottom of the SGS cell’s storage curve. This water level result is recorded at the cell centre, interpolated to the cell corners, and then the gridded outputs are triangulated from these points (orange line). In sheet flow situations when the volume in that cell is small, the cell-centered water level may sit below the terrain (blue dot on diagram) if the cell is steep enough. This can result in a water level results sitting below the DEM_Z, even when there is a positive depth result. Note this does not affect the simulation computationally, only how the water level results are output. <br>
[[File:SGS_Sheetflow_Waterlevel.jpg|600px]]
== How should below ground water surface elevation (WSE) in wet SGS cells be interpreted or presented? ==
Below ground WSE in wet SGS cells is a known output behaviour in SGS enabled models and does not indicate an error in the hydraulic solution.
This occurs because TUFLOW reports water level assuming water fills from the lowest part of the SGS cell during output. As a result, cells may be wet while the reported WSE remains below the cell centre ground level.
This behaviour commonly occurs in the following situations:
'''Channel edge partial wetting'''
* Partially wet cells along channel banks may contain water that does not reach the cell centre elevation.
* In this case, compare the standard WSE with the standard DEM_Z check file to confirm consistency with terrain levels.
'''Shallow sheet flow from rainfall or side inflow'''
Cells may be wet but still report WSE below the cell centre ground level because the depth is small and distributed across the SGS terrain.
'''Presentation and reporting considerations'''
* A presentation method is to post process results by adding the cell averaged depth output <font color="blue"><tt>SGS Depth Output</tt></font> <font color="red"><tt>==</tt></font><tt> CELL AVERAGE</tt> </font>to the DEM elevation to derive an above ground water level.
* This approach can improve the visual representation of shallow flooding in sheet flow areas but may produce unrealistic water levels in fully wet or partially wet cells.
* Conditional IF logic may be required to choose where to present cell averaged depth plus DEM and where to retain the standard TUFLOW water level output.
== Why do the high-resolution (HR) mapped results have a significantly smaller extent than the standard (non-HR) grid outputs for a sub-grid-scale (SGS) direct rainfall HPC model? ==
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The high resolution (HR) outputs are based on <u>[[TUFLOW_HR_Output | intersecting]]</u> the standard water level output results with the HR DEM_Z. Due to the <u>[[TUFLOW_Output_Discussion#Why_are_the_values_of_the_mapped_water_level_results_.28h_max.29_lower_than_the_terrain_elevations_.28DEM_Z.29.3F | output limitation]]</u> for sub-grid-scale (SGS) enabled models with shallow sheet flow (particularly direct rainfall models) on sufficiently steep terrain, water levels can be output lower than the DEM_Z terrain elevations. This is due to the assumption (for output purposes) that water fills the SGS cell’s storage curve from the bottom, which differs from the approach of cell-average depth used computationally in TUFLOW HPC and by default in depth outputs. When the HR water level results are processed, the full extent of the water level results are intersected with the HR DEM_Z and any water level results that are lower than the HR DEM_Z elevations due to the above effect are trimmed. The extent of the HR water level results are then used to trim the HR depth outputs.
== When should high-resolution (HR) outputs be used, and what are their limitations? ==
HR outputs are intended for visualisation and presentation because they retain sub-grid terrain detail but do not improve the underlying hydraulic calculations.
They are not suitable for assessment, benchmarking, or detailed analysis. Standard non-HR map outputs should be used for these purposes, and accuracy should be improved by refining the 2D cell size.
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