TUFLOW 1D2D Boundary Configuration Guidance - Revision history

Anne.Kolega: /* What are the differences between how HX and SX boundary cells treat volume and transfer flow? */ i.e.

2026-04-02T02:02:50Z

What are the differences between how HX and SX boundary cells treat volume and transfer flow?: i.e.

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	==What are the differences between how HX and SX boundary cells treat volume and transfer flow?==		==What are the differences between how HX and SX boundary cells treat volume and transfer flow?==
	HX are effectively head boundaries and do not contribute to storage (head boundaries of all types, 1D or 2D of any software, do not contribute to storage as the water level is set rather than solve the mass balance equation as done for normal cells). SX cell storage is used as per a normal cell. <br>		HX are effectively head boundaries and do not contribute to storage (head boundaries of all types, 1D or 2D of any software, do not contribute to storage as the water level is set rather than solve the mass balance equation as done for normal cells). SX cell storage is used as per a normal cell. <br>
	No flow is transmitted across HX cell sides except for those sides adjoining a normal cell (ie. active Code 1 cells). SX cells are like normal cells and can transmit across all four sides, i.e.:		No flow is transmitted across HX cell sides except for those sides adjoining a normal cell (i.e. active Code 1 cells). SX cells are like normal cells and can transmit across all four sides, i.e.:
	:*HX cells can transmit water to/from an adjoining SX cell.		:*HX cells can transmit water to/from an adjoining SX cell.
	:*HX cells can’t transmit to an adjoining HX cell.		:*HX cells can’t transmit to an adjoining HX cell.

Anne.Kolega: /* Stability of 1D/2D HX Configurations in TUFLOW HPC */

2026-02-27T02:31:41Z

Stability of 1D/2D HX Configurations in TUFLOW HPC

← Older revision		Revision as of 12:31, 27 February 2026
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	TUFLOW HPC inflow boundaries may experience recirculation when a uniform elevation is defined along the length of the boundary. This problem may also occur along HX boundaries in 1D-2D linked models that outflow from the 1D to the 2D domain. This is not a common configuration, though may occur when using a 1D channel to convey the flow from a dam break or similar along a defined channel onto floodplains in the 2D domain.		TUFLOW HPC inflow boundaries may experience recirculation when a uniform elevation is defined along the length of the boundary. This problem may also occur along HX boundaries in 1D-2D linked models that outflow from the 1D to the 2D domain. This is not a common configuration, though may occur when using a 1D channel to convey the flow from a dam break or similar along a defined channel onto floodplains in the 2D domain.

	Consider the 1D-2D linking shown in ~~Figure~~ ~~1.5~~ ~~The~~ HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command		Consider setting up the 1D-2D linking shown in the figure below; the HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command
	<font color="blue"><tt>HPC Boundary Approach </font> <font color="red">==</font> Method B</tt>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.		<font color="blue"><tt>HPC Boundary Approach </font> <font color="red">==</font> Method B</tt>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.

Anne.Kolega: /* 1D/2D SX Links Defined Using 1D Nodes (1d_nwk) */

2026-02-27T02:22:42Z

1D/2D SX Links Defined Using 1D Nodes (1d_nwk)

← Older revision		Revision as of 12:22, 27 February 2026
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	The modelled flow rates are shown in the figure below. As ~~can~~ ~~be seen~~, comparable peak flow rates are obtained regardless of the cell size (i.e. cell size convergence is demonstrated). The stability in the 1m cell size case has been improved markedly, though there are still some oscillations at low flows. <br>		The modelled flow rates are shown in the figure below. The figure demonstrates, comparable peak flow rates are obtained regardless of the cell size (i.e. cell size convergence is demonstrated). The stability in the 1m cell size case has been improved markedly, though there are still some oscillations at low flows. <br>

	[[File:1D2D Model Stability 005.png\|500px]]<br>		[[File:1D2D Model Stability 005.png\|500px]]<br>

Pavlina Monhartova: /* SX Boundary Lines (2d_bc) */

2025-01-07T02:44:48Z

SX Boundary Lines (2d_bc)

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	==SX Boundary Lines (2d_bc)==		==SX Boundary Lines (2d_bc)==
	2d_bc SX line features are often used to connect 1D structure to the 2D domain if the structure width is greater than one 2D cell wide (e.g.<u>[[Tutorial_M02 \|Tutorial Module 02]]</u>). This configuration not only increases the number of 1D/2D linking cells, it also has the added benefit of defining the 1D/2D boundary cells at the approximate location of the inlet/outlet of the 1D culvert. An additional benefit of this approach is that the "width" of the linking cells remains similar in length and location irrespective of 2D cell size. <br>		2d_bc SX line features are often used to connect 1D structure to the 2D domain if the structure width is greater than one 2D cell wide (e.g. <u>[[Tutorial_M02 \|Tutorial Module 02]]</u>). This configuration not only increases the number of 1D/2D linking cells, it also has the added benefit of defining the 1D/2D boundary cells at the approximate location of the inlet/outlet of the 1D culvert. An additional benefit of this approach is that the "width" of the linking cells remains similar in length and location irrespective of 2D cell size. <br>

	The 1D/2D linking cells in the 5m, 2m and 1m cell size models are shown in the the figure below.<br>		The 1D/2D linking cells in the 5m, 2m and 1m cell size models are shown in the the figure below.<br>

Abrar.Alttahir: /* SX Boundary Lines (2d_bc) */

2025-01-07T01:37:35Z

SX Boundary Lines (2d_bc)

← Older revision		Revision as of 11:37, 7 January 2025
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	==SX Boundary Lines (2d_bc)==		==SX Boundary Lines (2d_bc)==
	2d_bc SX line features are often used to connect 1D structure to the 2D domain if the structure width is greater than one 2D cell wide (e.g. [[~~Tute_M02_QGIS_1d2d_Link#2d_bc_Link_as_Line_Object~~\|Tutorial ~~Module02~~]]). This configuration not only increases the number of 1D/2D linking cells, it also has the added benefit of defining the 1D/2D boundary cells at the approximate location of the inlet/outlet of the 1D culvert. An additional benefit of this approach is that the "width" of the linking cells remains similar in length and location irrespective of 2D cell size. <br>		2d_bc SX line features are often used to connect 1D structure to the 2D domain if the structure width is greater than one 2D cell wide (e.g.<u>[[Tutorial_M02 \|Tutorial Module 02]]</u>). This configuration not only increases the number of 1D/2D linking cells, it also has the added benefit of defining the 1D/2D boundary cells at the approximate location of the inlet/outlet of the 1D culvert. An additional benefit of this approach is that the "width" of the linking cells remains similar in length and location irrespective of 2D cell size. <br>

	The 1D/2D linking cells in the 5m, 2m and 1m cell size models are shown in the the figure below.<br>		The 1D/2D linking cells in the 5m, 2m and 1m cell size models are shown in the the figure below.<br>

Emilie Nielsen at 00:32, 23 September 2024

2024-09-23T00:32:14Z

← Older revision		Revision as of 10:32, 23 September 2024
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	==1D Timestep==		==1D Timestep==
	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.		Selection of a 1D timestep that is too large can cause instability. The <u>[https://docs.tuflow.com/classic-hpc/manual/latest/ TUFLOW Manual]</u> 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>		During real world studies it is good practice to check the 1D timestep sensitivity: <br>

Chris Huxley: /* Stability of 1D/2D HX Configurations in TUFLOW HPC */

2024-04-08T23:33:32Z

Stability of 1D/2D HX Configurations in TUFLOW HPC

← Older revision		Revision as of 09:33, 9 April 2024
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	Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command		Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command
	<font color="blue"><tt>HPC Boundary Approach ~~</tt>~~</font> <font color="red"~~><tt~~>==</font> Method B </tt>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.		<font color="blue"><tt>HPC Boundary Approach </font> <font color="red">==</font> Method B</tt>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.

	[[File:1D2DHXEnergyCorrection.png\|500px]]<br>		[[File:1D2DHXEnergyCorrection.png\|500px]]<br>

Chris Huxley: /* Stability of 1D/2D HX Configurations in TUFLOW HPC */

2024-04-08T23:33:08Z

Stability of 1D/2D HX Configurations in TUFLOW HPC

← Older revision		Revision as of 09:33, 9 April 2024
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	Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command		Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command
	<font color="blue"><tt>HPC Boundary Approach </tt></font> <font color="red"><tt>==</tt> Method B </~~font~~>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.		<font color="blue"><tt>HPC Boundary Approach </tt></font> <font color="red"><tt>==</font> Method B </tt>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.

	[[File:1D2DHXEnergyCorrection.png\|500px]]<br>		[[File:1D2DHXEnergyCorrection.png\|500px]]<br>

Chris Huxley: /* Stability of 1D/2D HX Configurations in TUFLOW HPC */

2024-04-08T23:32:49Z

Stability of 1D/2D HX Configurations in TUFLOW HPC

← Older revision		Revision as of 09:32, 9 April 2024
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	TUFLOW HPC inflow boundaries may experience recirculation when a uniform elevation is defined along the length of the boundary. This problem may also occur along HX boundaries in 1D-2D linked models that outflow from the 1D to the 2D domain. This is not a common configuration, though may occur when using a 1D channel to convey the flow from a dam break or similar along a defined channel onto floodplains in the 2D domain.		TUFLOW HPC inflow boundaries may experience recirculation when a uniform elevation is defined along the length of the boundary. This problem may also occur along HX boundaries in 1D-2D linked models that outflow from the 1D to the 2D domain. This is not a common configuration, though may occur when using a 1D channel to convey the flow from a dam break or similar along a defined channel onto floodplains in the 2D domain.

	Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command ~~HPC Boundary Approach == Method B. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.~~		Consider the 1D-2D linking shown in Figure 1.5 The HX boundary “HXb1” shown in red is connected at each end to the same 1D node, whereas the remaining HX boundaries shown in purple are connected at each end to different 1D nodes. In the case that the flow is leaving the 2D domain to enter the 1D channel, the boundary is usually stable without energy correction, however for the reverse case, under high flow velocity conditions, the boundary may display instability or recirculation. If this does occur the problem may be remedied via an energy correction, using the command
			<font color="blue"><tt>HPC Boundary Approach </tt></font> <font color="red"><tt>==</tt> Method B </font>. Note that this will likely cause water level lines to display some discontinuity between the 1D and 2D domain across the boundary.

	[[File:1D2DHXEnergyCorrection.png\|500px]]<br>		[[File:1D2DHXEnergyCorrection.png\|500px]]<br>


	=1D/2D Modelling Webinar=		=1D/2D Modelling Webinar=

Chris Huxley at 22:29, 8 April 2024

2024-04-08T22:29:14Z

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 = Stability of 1D/2D SX Configurations =
 With the release of TUFLOW HPC (in 2017) and the continuous improvement of GPU hardware compute capability, there is an industry trend for models of higher resolution. As such, the 2D cell size in flood models is becoming smaller and smaller. Testing has shown in some instances reducing the 2D cell size may lead to model instability at 1D/2D SX locations. This page discusses this observation, the cause and available methods to  correct the instability. Topics of discussion include: <br>
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 <br>
 <br>
 =1D/2D Modelling Webinar=