2D and 1D/2D models require domains, boundaries and interfaces that define areas where 1D or 2D flow occurs and connections or boundary conditions exist. These objects are defined in XPSWMM as layers comprised of polygons or polylines.
This page contains the following topics:
To add 2D object layers:
- Right-click 2D Model in the Layer Control Panel.
- In the pop-up menu, select Add New Layer to display the available objects.
- Left-click the object to add to the model, and enter the name of the object layer and other information requested by the software.
The following objects may be used in a Quadtree, 2D, or 1D/2D model:
Layer | Object Type | Description or Purpose |
---|---|---|
polygon | Ultimate boundary of 2D model. Grid or Quadtree extents are available options | |
Quadtree Levels | polygon | Allows you to insert a Quadtree level (2-9) into your 2D model |
polygon | Areas where 2D flow can occur | |
polygon | Areas where 2D flow cannot occur such as buildings or raised fill or channels modeled in 1D | |
polygon | Areas where the grid cells are assigned an initial water surface elevation | |
polyline | Interface between 1D channel and 2D flood plain that within an active 2D area | |
polyline | Defined between the 1D node and the 1D/2D interface, it links the 1D node level to interface between the1D channel and the 2D floodplain | |
polyline | Interface between two 2D Grid domains and lies along the respective shared grid boundaries | |
polyline | Time dependent 2D head boundary that lies within an active 2D area | |
polyline | Time dependent 2D flow boundary that lies within an active 2D area | |
polygon | Areas of a rainfall, runoff hydrograph or user defined hydrograph. Flow id directed to cell with lowest elevation. | |
Polygon | Areas with defined infiltration and/or roughness characteristics | |
2D Flow Constrictions | Polygon | Applies the affect of flow constrictions based on defined flow area/constriction levels |
Polyline | Head dependent 2D flow boundary that lies within an active 2D area | |
Polyline | Time to inundate based on defined flood levels |
Extents
These polygons define the boundary of a domain in the 2D model. A grid with equal horizontal and vertical cell size and orientation extends over the polygon. Multiple Grid Extents are possible depending on software licensing. To check for this capability go to Help > License to check for 2D multiple domains in the License Details.
Grid Extents
You can manually add 2D Grid Extent polygons or import these shapes as shown in the 2D Object Creation section. This is also available with Multiple 2D domains for XP2D Classic.
Use the properties dialog to modify the grid size and display properties.
Quadtree Extents
The Quadtree Extents is single domain only (one polygon), and is available without Multiple 2D domains. This is applicable when XP2D Extreme Quadtree is selected in 2D Job Control Settings.
Use the properties dialog to modify the grid step size, orientation angle, cell count, and other properties.
Multiple Grid Extent polygons
Multiple 2D domains (Grid Extent polygons) are supported as an additional licensed module. Each domain has its own grid extents, grid cell size, time step (optional) and orientation. Domains may be linked by 2D / 2D Interface polylines. This is only applicable for XP2D Classic.
Grid Extent layers may be moved up and down within the Layer Control Panel by right-clicking a given grid layer and selecting Move this Layer Up or Move this Layer Down, to allow ordering of multiple domains. As shown in the Layer Control Panel, a higher domain in the layer list takes precedence over all domains below it in the list, where there are overlaps between extent polygons (that is, the top most grid layer will take precedence over all other grid layers).
Quadtree Levels
The Quadtree Levels define the levels of nesting that will be implemented in your 2D model, which allows for a focused calculation resources on areas of most interest. This functionality is applicable for XP2D Extreme and requires multiple domain licenses.
The available levels are 2-9, and has the following properties:
- ½ cell size per level
- Multiple polygons per level
- Level polygons can be nested or standalone (i.e., you can skip a level)
You can insert a Quadtree level into your 2D model by selecting from the drop-down list. Levels that are already added will no longer be available in the list.
Active and Inactive 2D Areas
These polygons define the area where 2D flow can and cannot occur. A model may have multiple 2D active and inactive areas. An inactive area is considered to be bounded by a vertical wall with an infinite height.
The default area type determines if Active or Inactive 2D areas should be defined. The default area type is specified in 2D Job Control Settings. Additional 2D cells first take on the default area type and then can be altered by Active or Inactive areas. In a case where multiple polygons overlap the cell will take on the default area,
Default Area Type | User defined areas |
---|---|
Active | Inactive |
Inactive | Active |
You can manually add Active or Inactive Area polygons or import these shapes as shown in the 2D Object Creation section.
Initial water levels
The 2D Initial Water Levels layer allows the use of polygons to be drawn within the 2D Grid to set initial water surface elevations for the given polygon areas. Note that the value input for the initial water level is an elevation, not a depth value.
The Initial Water Level can be set such that all 2D cells will be dry at the onset of a simulation. This is accomplished by setting the initial water level at an elevation below the lowest point on the surface in the model.
Users can manually add Initial Water Level polygons or import these shapes as shown in the 2D Object Creation section.
1D/2D Interface
The 1D/2D interface is a polyline indicating the boundary between the 2D floodplain (Active 2D area) and the top of the 1D channel.
Notes
- A 1D/2D interface must overlay the boundary of an Active 2D area i.e., the vertices of the 2 objects must coincide.
- A 1D/2D connection extends from a vertex of a 1D/2D interface to a 1D node
- Each end of the 1D/2D interface must have a 1D/2D connection.
- You can manually add 1D/2D Interface lines or import these shapes as shown in the 2D Object Creation section
HX and SX Interface Lines
It is possible to switch a 1D/2D interface polyline from an HX line (default) to an SX line by double-clicking the polyline and changing its type from head interface (HX) to flow interface (SX).
The HX line operates as a head boundary for the 2D cells - the water level in the 2D cells comes from the 1D model, any water entering or leaving the 2D model is added/removed from the 1D. This forces a flow boundary to the 1D. In the 2D boundary the HX stands for Head from an eXternal model (in this case the external model is the 1D). HX is recommended for use when interfacing between 2D cells and a 1D node, where the 2D cells are larger than the connecting 1D system. An HX line is typically recommended when interfacing between a 1D open channel and 2D overbank/overland flow areas.
The SX boundary (Source from an eXternal model) is a sink source boundary to the 2D cells, this becomes a 1D water level boundary. The SX or flow interface polyline is recommended for use when interfacing between 2D cells and a 1D node, where the 2D cells are smaller than the connecting 1D system. An SX line is recommended when interfacing between a dense 2D grid and large culvers, for example.
Further information on the both HX and SX interface lines can be found in the TUFLOW manual.
1D/2D Interface Line Profile Tool
Along any 1D/2D Interface line, there are three elevations of concern: 1. The elevation of the Grid Cells; 2. The Interpolated Bank elevations; and 3. The Interpolated Bed elevations. This tool enables the user to see the relationship along the 1D/2D Interface line at its current position. When the profile is created, a warning will be generated if there are any inconsistencies. A thick Ridge Line can be created to raise the local cell elevations to the channel Bed, or the Channel Bank. Alternatively, the 1D/2D interface line can be relocated to minimize these inconsistencies.
1D/2D Connections
1D/2D Connections are polylines representing hydraulic links between 1D/2D Interface polyline vertices and 1D nodes. At each time step, the HGL in the 2D boundary and the 1D node are evaluated.
The Ponding selection of Link Spillcrest to 2D or Link Invert to 2D must also be selected in 1D/2D simulations for all nodes with 1D/2D Connection lines. If there is a node with 1D/2D Connections snapped an no selection of Link to 2D, an error will be generated and the simulation cannot proceed. Simply connecting the node with the 1D/2D Connection polyline is not enough.
You can manually add 1D/2D Connections lines or import these shapes as shown in the 2D Object Creation section.
- 1D/2D Interface polyline(s) should be defined before 1D/2D Connections are created. The 1D/2D Interface polyline must be visible for Snap Mode to function properly.
- Importing 1D/2D Connection polylines is NOT the recommended way to apply these items to a model. Manually connecting nodes to appropriate 1D/2D Interface polyline vertices is the appropriate method. The reason for this is that the imported 1D/2D connection lines will may be snapped to the appropriate connection points as they are when manually applied, these snapped or fused points are a requirement for the connections to be properly connected.
2D/2D interfaces
2D/2D Interfaces consists of a polyline which connects the vertices between two Grid Extents allowing hydraulic flow to be transferred from one Grid Extent to another.
You can manually add 2D/2D Interface lines or import these shapes as shown in the 2D Object Creation section.
The 2D/2D Interface connection data can be updated or modified by selecting and right-clicking on a 2D/2D Interface polyline, and selecting the Edit Data option..
The 2D/2D Interface Connection Data includes inputs of the First and Second, or Dominant and Secondary, 2D Grid Domains. The order of the First and Second Domains does not impact the hydraulic model.
The Minimum Distance Between 2D/2D Water Level Control Points Between Vertices Along the 2D Line is recommended at least two times the larger grid cell (between the two Grid Domains). If a zero value is input only the vertices along the 2D polyline are used.
Note
In version 2013 and later, a Warning message will appear if any elevations along the 2D/2D interface line are below the initial water level.
2D Head Boundary
The 2D head boundary is a polyline representing a time dependant head at an edge of a 2D Active Area. Vertices of a 2D head boundary must be coincident with vertices of a active 2D area – i.e. the 2D Head Boundary must be placed within the extents of an active 2D grid area.
Free Outfall in 2D
A 2D head boundary which is set at or below the draped 2D cell levels will force a free outfall to occur for all flows which enter the connecting cells for all flow rates. This procedure works as the cells adjacent to the head boundary covered cells will see dry adjacent cells and free flow into these dry adjacent cells will be allowed. The 2D head boundary covered cells will always be dry because the head level at these cells is forced to be below the cell level, essentially letting any flow volume which enters the given cells to fall through the cell and out of the 2D model space. This can be thought of as pushing the flow under the cells, which removes the flow from the model at a free outfall rate.
You can manually add Head Boundary lines or import these shapes as shown in the 2D Object Creation section
To launch the Boundary Condition dialog, double-click a head boundary line, or right-click and select Edit Data.
Use this dialog to specify the time dependency of the boundary condition:
- Choose insert button to create blank rows.
- Enter the data in the cells or copy and paste from other application such as text file or a spreadsheet.
Time is in decimal hours since the start of the 2D simulation. The second column is the head (ft or m).
2D Flow Boundary
The 2D flow boundary is a polyline representing a time dependant flow at an edge of a 2D active area. Vertices of a 2D Flow boundary must be coincident with vertices of an active 2D area.
Right click on a selected Flow Boundary line, and choose Edit Data to launch the Boundary Condition dialog.
To specify the time dependency of the boundary condition:
- Choose insert button to create blank rows.
- Enter the data in the cells or copy and paste from other application such as text file or a spreadsheet.
Time is decimal hours since the start of the 2D simulation. The second column is the flow (in ft^{3}/s or m^{3}/s).
2D Rainfall/Flow Areas
2D Rainfall Flow Ares are polygons used to define area of rainfall, runoff hydrographs or users defined hydrograph
You can manually add 2D Rainfall/Flow Areas or import these shapes as shown in the 2D Object Creation section
To edit the data for a 2D Rainfall Flow Area polygon:
- Select the polygon, right click and choose Edit from the popup menu
- In the Select the appropriate radio button to indicate the type of data. Enter the required data:
For Rainfall, select a rainfall from the Global Database
For Hydrograph, select a Runoff node.
For User Defined Flow Hydrograph, enter the times series flow data.
2D Landuses
2D Landuses are polygons used to define areas of roughness and/or infiltration characteristics. 2D Lands Uses are defined in the Global Database.
Users can manually add 2D Landuse polygons or import these shapes as shown in the 2D Object Creation section
To edit the Landuse polygon data
Select the polygon(s) right-click and choose Properties from the popup menu.
Select the data tab to update roughness and Infiltration (optional) directly in the Global Database record for the given Landuse. Suggested roughness values can be found on Roughness Coeficients.
Note that when 2D Landuse polygon areas overlap attributes, the Landuse highest in the Layer Control Panel list will be used during the simulation. The top most Landuse in the layer list takes precedence over all other Landuse Layers.
To adjust the order of priority of the Landuse layer list, right click on a land use and select Move this Layer Up, or Move this Layer Down.
To change the associated Global Database record for the polygon, choose Landuse from the pop-up menu then select the Landuse from the list.
2D Flow Constrictions
Flow Constrictions allow the user to create points, lines and polygons that modify the 2D cell sides flow width, percentage blockage and additional energy losses. They are designed for 2D flow under and over bridges, pipes and other obstructions across a waterway.
There are three types of Flow Constrictions available in XP2D: Bridge Deck, Floating Deck and Layered – these items are discussed below. The following schematic shows the three types of Flow Constriction types at-a-glance.
Layered
Layered flow constrictions allow the attributes to be varied with water depth. This provides the opportunity to model in 2D the flow under and over a bridge deck, or a pipeline crossing a waterway.
Up to four layers are represented, with the bottom three layers each having their own attributes. The top, fourth, layer assumes the flow is unimpeded (eg. flow over the top of a bridge). Within the same shape, the invert of the bed, and thickness of each layer can vary in 3D. Each layer is assigned its own percentage blockage and energy loss coefficient.
Layered flow constrictions function by adjusting the flow width of the 2D cell so as to represent the combination of blockages of the four layers, and by accumulating the energy losses. When the flow is only within Layer 1, only the attributes of Layer 1 are applied. As the water level rises into Layer 2, the influence of the Layer 2 attributes increase as the water continues to rise; similarly for Layer 3 and Layer 4.
The cell side flow width is calculated by summing the flow areas of each layer (including the effects of layer blockages), and dividing by the water depth.
Energy Loss Coefficient. Energy loss coefficient is sometimes referred to as form loss coefficient. This relates to the energy loss applied each layer of the structure. It is used for modelling fine-scale “micro” contraction-expansion losses not picked up by the change in the 2D domain’s velocity patterns, e.g. by the losses caused by bridge piers.
Note: So that this attribute is independent of 2D cell size, it has different treatment depending on the object it is attached to as follows:
Line: For thin lines, the Energy Loss Coefficient value is applied to the cell sides unchanged. For thick (whole cell) lines, the Energy Loss Coefficient value is divided by two (two cell sides in the direction of flow). For wide lines the Energy Loss Coefficient value is divided by the number of cells across the line (i.e. the line’s width divided by the cell size) and applied to all cell-sides.
Polygon: Energy Loss Coefficient is the form loss per metre length (in the predominant direction of flow). Energy Loss Coefficient values are not dependent on the flow width, but are on the length of travel in the direction of flow. However, if a negative Energy Loss Coefficient value is specified, the absolute value is taken and applied unadjusted to all cell-sides affected by the shape. Note that this is not cell size independent, therefore if the 2D cell size is changed, this attribute also needs to be changed.
Energy loss should be used as a calibration parameter.
The form loss coefficient is applied as an energy loss based on the dynamic head equation below where is the FLC value.
% Blockage. The percentage blockage of the cells in each layer. For example, if 40 is entered (i.e. 40%), the cell sides are reduced in flow width by 40%, i.e. the cell side is set to 0.6 times the full flow width.
The lower part of the table shows the physical geometry of the structure for each vertex. If applying variable invert and obvert values, the vertex is highlighted on the Plan view when a cell is selected in that vertex row.
Z of DTM. For reference the Z value of the DTM at the each vertex location is shown.
Constant Invert/Variable Invert. The invert (ground level) of the flow constriction (above datum) can be edited from the DTM value. By clicking in the right of the Constant Invert cell a drop down is available to enter a Constant Invert value for each vertex, or to enter Variable Invert if each vertex has a different value.
Constant Obvert/Variable Obvert. The obvert (soffit) of the flow constriction (above datum) represents the top of each layer. By clicking in the right of the Constant Obvert cell a drop down is available to enter a Constant Obvert value for each vertex, or to enter Variable Obvert if each vertex has a different value.
Invert adjusted by. The user can change all inverts by an entered value.
Invert modification type. The user can choose how the invert changes the Z values for the DTM.
Change All All values are changed from the Z of DTM value to match the values in the table.
Change None The Z of DTM value is used.
Max of Entered and DTM The maximum of the Z of DTM value and the value entered in the table is used.
Min of Entered and DTM The minimum of the Z of DTM value and the value entered in the table is used.
3D View A 3D view of the physical geometry of the Flow Constriction can be displayed. This shows the shape of the layer or layers with different shading. For example:
Limitations of layered flow constrictions
Lumped approach for energy loss: users may not be able to get the flow splits between the layers, say under the bridge and over the bridge.
2D Flow Constriction Areas can be manually added or imported as shown in the 2D Object Creation section.
Bridge Deck
Bridge Decks allows the user to model the percentage blockage and energy loss caused by flow constrictions such as piers under a bridge with the water being blocked above the obvert.
Energy Loss Coefficient (Above). Energy loss coefficient is sometimes referred to as form loss coefficient. This relates to the energy loss applied above the obvert (soffit) of the structure, in the Bridge Deck where it is completely blocked. It is used for modelling fine-scale “micro” contraction-expansion losses not picked up by the change in the 2D domain’s velocity patterns, e.g. by the losses caused by bridge piers.
Note: So that this attribute is independent of 2D cell size it has different treatment depending on the object it is attached to as follows:
Line: For thin lines, the Energy Loss Coefficient value is applied to the cell sides unchanged. For thick (whole cell) lines, the Energy Loss Coefficient value is divided by two (two cell sides in the direction of flow). For wide lines the Energy Loss Coefficient value is divided by the number of cells across the line (i.e. the line’s width divided by the cell size) and applied to all cell-sides.
Polygon: Energy Loss Coefficient is the form loss per metre length (in the predominant direction of flow). Energy Loss Coefficient values are not dependent on the flow width, but are on the length of travel in the direction of flow.
However, if a negative Energy Loss Coefficient value is specified, the absolute value is taken and applied unadjusted to all cell-sides affected by the shape. Note that this is not cell size independent, therefore if the 2D cell size is changed, this attribute also needs to be changed.
Energy loss should be used as a calibration parameter.
The form loss coefficient is applied as an energy loss based on the dynamic head equation below where is the FLC value.
Energy Loss Coefficient (Below). This relates to the energy loss applied below the obvert (soffit) of the structure and is applied as described above.
% Blockage. The percentage blockage of the cells. For example, if 40 is entered (i.e. 40%), the cell sides are reduced in flow width by 40%, i.e. the cell side is set to 0.6 times the full flow width.
Additional Manning’s n. This can be used to introduce additional flow resistance once the upstream water level reaches the bridge deck obvert (or soffit). The additional flow resistance is modelled as an increase in bed resistance by increasing the wetted perimeter at the cell mid-side by a factor equal to (2.*Bed_n)/Additional_n. For example, if the Additional Manning’s n and the bed Manning’s n values are the same, the wetted perimeter is doubled, thereby reducing the conveyance and increasing the resistance to flow. To be used as a calibration parameter to fine-tune the energy losses across a bridge or floating structure.
The lower part of the table shows the physical geometry of the structure for each polyline or polygon perimeter vertex. If applying variable invert and obvert values, the vertex is highlighted on the Plan view when a cell is selected in that vertex row.
Z of DTM. For reference the Z value of the DTM at the each vertex location is shown.
Constant Invert/Variable Invert. The invert (ground level) of flow constriction (above datum) can be edited from the DTM value. By clicking in the right of the Constant Invert cell a drop down is available to enter a Constant Invert value for each vertex, or to enter Variable Invert if each vertex has a different value.
Constant Obvert/Variable Obvert The obvert (soffit) of flow constriction (above datum) represents the underside of the Bridge Deck. By clicking in the right of the Constant Obvert cell a drop down is available to enter a Constant Obvert value for each vertex, or to enter Variable Obvert if each vertex has a different value.
Invert modification type. The user can choose how the invert changes the Z values for the DTM.
Change All. All values are changed from the Z of DTM value to match the values in the table.
Change None. The Z of DTM value is used.
Max of Entered and DTM. The maximum of the Z of DTM value and the value entered in the table is used.
Min of Entered and DTM. The minimum of the Z of DTM value and the value entered in the table is used.
D View. A 3D view of the physical geometry of the Flow Constriction can be displayed. This shows the shape of the layer or layers with different shading. E.g.
Floating Deck
Floating Deck allows the user to model the percentage blockage and energy loss caused by flow constrictions such as floating pontoons where part of the structure affects the flow of water under the surface.
- Floating Deck is not available in XP2D Extreme. It is only applicable for XP2D Classic.
- When XP2D Extreme is used, the Floating Deck constriction will not be exported to the engine, so the data does not disappear, but you are encouraged to migrate to the Layered flow constrictions.
Energy Loss Coefficient (Above). Energy loss coefficient is sometimes referred to as form loss coefficient. This relates to the energy loss applied above the obvert (soffit) of the structure, in the Floating Deck it is completely blocked above the water level. It is used for modelling fine-scale “micro” contraction-expansion losses not picked up by the change in the 2D domain’s velocity patterns, e.g. by the losses caused by bridge piers.
Note: To have this attribute independent of 2D cell size, it can have different treatment depending on the object it is attached to, as follows:
Line: For thin lines, the Energy Loss Coefficient value is applied to the cell sides unchanged. For thick (whole cell) lines, the Energy Loss Coefficient value is divided by two (two cell sides in the direction of flow). For wide lines the Energy Loss Coefficient value is divided by the number of cells across the line (i.e. the line’s width divided by the cell size) and applied to all cell-sides.
Polygon: Energy Loss Coefficient is the form loss per metre length (in the predominant direction of flow). Energy Loss Coefficient values are not dependent on the flow width, but are on the length of travel in the direction of flow. However, if a negative Energy Loss Coefficient value is specified, the absolute value is taken and applied unadjusted to all cell-sides affected by the shape. Note that this is not cell size independent, therefore if the 2D cell size is changed, this attribute also needs to be changed.
Energy loss should be used as a calibration parameter.
The form loss coefficient is applied as an energy loss based on the dynamic head equation below the FLC value.
Energy Loss Coefficient (Below). This relates to the energy loss applied below the water level for a Floating Deck and is applied as described above.
% Blockage. The percentage blockage of the cells. For example, if 40 is entered (i.e. 40%), the cell sides are reduced in flow width by 40%, i.e. The cell side is set to 0.6 times the full flow width.
Additional Manning’s n. This can be used to introduce additional flow resistance for the Floating Deck. As the deck soffit is permanently submerged this is always applied. The additional flow resistance is modelled as an increase in bed resistance by increasing the wetted perimeter at the cell mid-side by a factor equal to (2.*Bed_n)/Additional_n. For example, if the Additional Manning’s n and the bed Manning’s n values are the same, the wetted perimeter is doubled, thereby reducing the conveyance and increasing the resistance to flow. To be used as a calibration parameter to fine-tune the energy losses across a bridge or floating structure.
The lower part of the table shows the physical geometry of the structure for each polyline or polygon perimeter vertex. If applying variable invert and obvert values, the vertex is highlighted on the Plan view when a cell is selected in that vertex row.
Z of DTM. For reference the Z value of the DTM at the each vertex location is shown.
Constant Invert/Variable Invert. The invert (ground level) of flow constriction (above datum) can be edited from the DTM value. By clicking in the right of the Constant Invert cell a drop down is available to enter a Constant Invert value for each vertex, or to enter Variable Invert if each vertex has a different value.
Constant Depth/Variable Depth. The depth of the flow constriction represents the depth of the Floating Deck into the water (i.e. depth below the water line). By clicking in the right of the Constant Depth cell a drop down is available to enter a Constant Depth value for each vertex, or to enter Variable Depth if each vertex has a different value.
Invert modification type. The user can choose how the invert changes the Z values for the DTM.
Change All. All values are changed from the Z of DTM value to match the values in the table.
Change None. The Z of DTM value is used.
Max of Entered and DTM. The maximum of the Z of DTM value and the value entered in the table is used.
Min of Entered and DTM. The minimum of the Z of DTM value and the value entered in the table is used.
2D Head/Flow (HQ) Boundary
The 2D Head-Flow (HQ) boundary is a polyline representing a rating curve based 2D outfall and is similar to the 1D outfall Type 5 – user rating curve. Like other 2D boundary conditions, the vertices of a 2D HQ boundary must be coincident with vertices of an active 2D area – i.e. the 2D Head Boundary must be placed within the extents of an active 2D grid are.
You can manually add HQ Boundary lines or import these shapes as shown in the 2D Object Creation section
When Edit Data is selected, the following dialog appears.
You can either allow outfall flow to occur by specifying the Water Surface Slope (ft/ft or m/m), or you can enter an HQ curve to dictate the flow across the boundary.
Use this dialog to specify the stage-flow dependency of the boundary condition.
Choose insert button to create blank rows.
Enter the data in the cells or copy and paste from other application such as text file or a spreadsheet.
Flow is entered as either ft^{3}/s or m^{3}/s; Water Level is the head (ft or m).
Note
If the slope option is used, very flat slopes can cause stability issues due to discrepancies which can occur between Water Surface Slope and bed slope. The minimum Water Surface Slope which is recommended is 0.1% (entered as 0.001 ft/ft or m/m). However, smaller slope values can be applied.
Evacuation Routes
The 2D Evacuation Routes layer allows users the option of assessing time to inundation level for chosen areas based on given criteria within a 2D model.
Route cut off criteria is defined by the following:
Depth: ft (m)
VxD: ft^{2}/s (m^{2}/s)
Velocity: ft/s (m/s)
Evacuation Route Modify Elevation options can be used to set relegations for the Evacuation Route polyline. This option allows users the flexibility to set route cut off criteria based on elevations different than what are represented by the surface. Either 2D Breakline (constant elevation) or 3D Breakline (variable elevation) Evacuation Route polyline references elevations can be used.