TUFLOW HR Output: Difference between revisions
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=Introduction=
High
Example models with high-resolution outputs are available in the <u>[[TUFLOW_Example_Models|TUFLOW Example Models]]</u> dataset.
For the HR output, the water level at each HR output location is interpolated from the computed 2D water levels (see <u>[[#Water_Level_Interpolation_Methods|Water Level Interpolation Methods]]</u> for details). The depth output is calculated differently for standard and high-resolution outputs:
:* Standard depth output: The depth is calculated at cell centres and corners first, then interpolated to the standard output grid locations (default is half the cell size). This is shown in the image on the left.
:* High-resolution depth output: The depth is the difference between the interpolated water level and the sub-grid elevation. This is shown in the image on the right.<br>
<br>
[[File:Sgs_std_output.png|360px]] [[File:Sgs_hr_output.png|360px]]
The advantage of the HR output is that it can retain the sub-grid detail of the terrain information even at a coarse cell size. As compared in the example below, the HR depth output shows a clear flow path even at a 100m grid. However, nicer depth output does not mean reliable hydraulic result. In fact, the 100m cell size is too coarse to produce reliable/converged hydraulic results for any real-world flood model. It's is strongly recommended that the model convergence/benchmarking tests
[[File:Sgs_std_vs_hr_output.png|720px]]
=Enable High
To produce high-resolution output, add “HRASC”, “HRFLT” or “HRTIF” to the “<font color="blue"><tt>Map Output Format </tt></font> <font color="red"><tt>==</tt></font>” .tcf command. Note that if a HR output is defined in this command,
:<font color="blue"><tt>Map Output Format </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>XMDF TIF HRTIF</tt></font>
:<font color="blue"><tt>HRTIF Map Output Data Types </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>h d</tt></font>
The map output data types and map output interval can be defined separately for the
:<font color="blue"><tt>Map Output
:<font color="blue"><tt>
:<font color="blue"><tt>
:<font color="blue"><tt>HRTIF Map Output Interval </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>3600</tt></font> <font color="green"><tt>! Sets HR (TIF format) map output interval to 3600 seconds</tt></font>
The output resolution for high-resolution output grids can be defined using the following .tcf command. It can be defined in meters or feet. If this command is omitted, the default output resolution is set to the SGS sampling distance:
:<font color="blue"><tt>HR Grid Output Cell Size </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>0.5</tt></font> <font color="green"><tt></tt></font>
HR outputs are supported by HPC and Quadtree Output Zones. Below is an example of .tcf commands to set up HR output in
<font color="blue"><tt>Model Output Zones</tt></font> <font color="red"><tt>==</tt></font> <font color="black"><tt>ZoneA</tt></font><br>
<font color="blue"><tt>Define Output Zone</tt></font> <font color="red"><tt>==</tt></font> <font color="black"><tt>ZoneA</tt></font>
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<font color="blue"><tt>End Define</tt></font>
Similar to the standard output, the HR output needs to interpolate cell centre water levels to cell corners. However, the interpolation methods for the standard output (<font color="blue"><tt>Map Output Corner Interpolation </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>Method C</tt></font>) can produce "bumpy" HR water level
▲=Water Level Interpolation Method=
▲Similar to the standard output, the HR output needs to interpolate cell centre water levels to cell corners. However, the interpolation methods for the standard output (<font color="blue"><tt>Map Output Corner Interpolation </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>Method C</tt></font>) can produce "bumpy" HR water level output in direct rainfall models with steep terrain, as the water level is linearly interpolated from the cell centres/corners, while the change of sub-grid elevations may not be linear. This often happens between fully wet cells and sheet flow cells, as illustrated below.
[[File:corner_h_intp_output.png|480px]]
In the HR water level output, these locations
[[File:HR_Intp_A.png|480px]]<br>
'''Method A HR Interpolation Approach
Two additional methods have been added for the HR corner water level interpolation:
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* Method C is the default option that applies the same sheet flow checks as the Method B. In addition, it also uses the number of wet SGS sampled points as a weighting that biases non-sheet flow cells that further improves the mapping to in-stream water levels.
The two images below present the high-resolution water level output at the same location, but with <tt><font color=blue>HR Interpolation Approach </font><font color=red>==</font> Method B</tt> and
[[File:HR_Intp_B.png|480px]] [[File:HR_Intp_C.png|480px]]<br>
'''
Note that when these two methods are applied, the interpolated corner water level is biased to the non-sheet flow cells, and consequently, sheet flow cells may appear as “dry” cells. The improved approach that takes into the account of the sheet flow water level is currently under development. ▼
▲Note that when these two methods are applied, the interpolated corner water level is biased to the non-sheet flow cells, and consequently, sheet flow cells may appear as “dry” cells. The improved approach
Whilst Methods B and C can substantially improve the water surface mapping of SGS models using direct rainfall (rain-on-grid), there will always be inaccuracies with mapping at a higher resolution than the 2D cell resolution due to interpolation and extrapolation. Regardless of the software, the greater the ratio of 2D cell size to the high-resolution DEM cell size, the greater the potential for mapping inaccuracies. Should better mapping accuracy be required, reducing the 2D cell size to compute the spatial variation in water surface and velocities more accurately is, by far, the best course of action. ▼
▲Whilst Methods B and C can substantially improve the water surface mapping of SGS models using direct rainfall (rain-on-grid), there will always be inaccuracies with mapping at a higher resolution than the 2D cell resolution due to interpolation and extrapolation. Regardless of the software, the greater the ratio of 2D cell size to the high-resolution DEM cell size, the greater the potential for mapping inaccuracies. Should better mapping accuracy be required, reducing the 2D cell size to compute the spatial variation in water surface and velocities more accurately is
=Interpolation near Thin
Thin breaklines are often used to define hydraulic controls, such as levees and road embankments. These controls often experience upstream controlled weir flow, where the water levels on the two sides of the breakline can be considerably different. Retaining just one water level (upstream, downstream or average) at output points along the breakline may result in unsatisfactory water level map output as illustrated in the two figures below. This issue becomes more profound the larger the 2D cell size.
: '''Note:'''
[[File:breakline_h_intp_output.png|480px]]<br>
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'''HR Thin Z Line Output Adjustment == OFF'''
A new HR output feature has been
<font color="blue"><tt>HR Thin Z Line Output Adjustment </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>OFF | {ON CELL SIDES} | ON ALIGNMENT</tt></font>
*
*
*
[[File:HR_thin_brk_on.png|480px]] [[File:HR_thin_brk_on_adj.png|480px]]<br>
'''HR Thin Z Line Output Adjustment == ON CELL SIDES (left) and ON ALIGNMENT (right)'''
▲Note the this feature (at present) only works for thin breaklines in Z Shape (2d_zsh) layers. Thick/wide breaklines raises more than 1 rows of cell centres and 2 rows of cell faces, and thus do not experience similar HR interpolation issue.
When modelling breaklines in TUFLOW, thin breaklines modify the cell face elevations but do not modify the cell storages. When outputting the high-resolution outputs, the user can choose whether the cell face elevations are included using the following .tcf command.
<font color="blue"><tt>HR Grid Output Use Face Elevations </tt></font> <font color="red"><tt>== </tt></font> <font color="black"><tt>{ON} | OFF</tt></font>
* ON (default): Use face elevations in [[Check_Files_2d_DEM_Z_HR | _DEM_Z_HR]] check file. This option accurately shows the cell faces where water can be hydraulically blocked. However, when cell faces are angled with the thin breakline, this can create 'pockets' of lower elevations in the check file that do not exist in reality.
* OFF: Face elevations are not used in [[Check_Files_2d_DEM_Z_HR | _DEM_Z_HR]] check file. This is an useful option for report writing, as 'clean' high-resolution DEM images can be generated reflecting all geometry updates except for the Thin Breakline updates at cell faces.
[[File:HR_Z_Use_Face_Elevations_ON.PNG|480px]] [[File:HR_Z_Use_Face_Elevations_OFF.PNG|480px]]<br>
'''HR Grid Output Use Face Elevations == ON (left) and OFF (right)'''
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▲=Showing Face Elevation in HR_Z Check File =
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