The 1D - 2D button launches the 2D Analysis Criteria form to allow a 1D - 2D analysis of the current phase.
1D – 2D Linking - Method of Exchanging Water with Surface
When running a 1D – 2D Analysis Junctions, Connections and Stormwater Controls (the 1D network) will be linked with the 2D Surface. This section will explain the methods used for each structure to exchange water with the surface.
The 1D - 2D Analysis uses the 1D simulation engine (Analysis) in combination with a 2D simulation engine (2D - Method of Analysis). This is to enable InfoDrainage to represent (i) the overflow from the sewer/channel network, (ii) the movement of the flooded water on the surface, (iii) the re-entrance of the flooded water in the sewer/channel network.
The 1D simulation engine and the 2D simulation engine run simultaneously during the 1D - 2D analysis in order to enable a dynamic coupling between the 2 engines. Each simulation engine runs with its own computational time-step, and the 2 engines sync up at regular intervals (the interval is the max value of the 1D time-step range, see Simulation Health)Note that InfoDrainage automatically uses shorter computational time-steps for the 1D - 2D analysis to prevent the onset of oscillatory behaviors.
There are 3 ways the exchange between the 2 engines can happen in InfoDrainage: at manholes, along the banks of open channels, along the outline of SWCs.
The overflow can happen in one location, while the re-entrance of the flooded water can happen in a different location (of any of the 3 types above), depending on whether the flooded water will move on the surface after coming out of the 1D network. There are no limits on how many locations the water can be exchanged, or how many times the water is exchanged. So, for example, InfoDrainage can be used to represent flooding coming out of an open channel, then the flood waters flow on the surface to some lower ground where the water is captured by a Pond SWC, but eventually this pond fills up and floods itself, the flood waters flow further away following the terrain slope and features, and end up near a manhole where it is captured and goes into a conduit. Note that in this example the open channel, the pond and the manhole do not need to be connected by the same 1D network, they can be connected to different outfalls.
The computation of the exchange between the 1D network and the 2D surface accounts for the respective heads at the location of the possible exchange. The flow exchanged is calculated using an orifice equation for the manholes, and a weir equation for the channel banks and SWC outline. For the latter, due to their linear nature, the weir is split in multiple segments (accounting for vertices in the 2D mesh) and hydraulic calculations are done on each individual segment.
The 1D - 2D Analysis is typically more computationally intensive than the regular (1D only) Analysis, due to the extra effort of running the 2D engine and the overhead of the exchange between the 2 engines. The increase in analysis time depends on factors like: the amount of water in the 2D domain, the percentage of the 2D domain that is wet, how fast the water is moving on the 2D domain, how many locations the water is exchanged between the 2 engines.
Representation of the 1D - 2D Exchange
This section describes the approach used for each structure in order to exchange water with the surface.
These structures exchange water with the surface using what we call a point-based implementation. These structures exchange water with the surface at one point in the 2D domain.
For Manholes, the software uses the point in the center of the manholes (dictated by the easting and northing) and calculates which element of the 2D mesh contains the location of this point. The hydraulic head at this particular element is used in the orifice calculations in conjunction with the head in the manhole itself. This element receives the overflow water from the 1D network or provides the water that goes back into the 1D network. Sealed manholes do not exchange water with the surface.
For the point-based Stormwater Controls we use the icon location to determine what mesh element is connected to the SWC. However, if the icon is outside of the SWC outline then the nearest point of the outline is used instead, to ensure water is still correctly exchanged within the outline of the structure at the nearest location to the icon. E.g. where the leader line connects
These structures exchange water with the surface along a linear feature: the sides of the channel (i.e. the banks) or the outline of the SWC. Therefore, these structures are connected to more than one mesh element in the 2D domain.
For open channels, the side banks are created using the U/S and D/S cover elevations, or the U/S and D/S cross-sections for a Custom section channel. A bank is made of multiple segments, with bank points matching the locations of mesh vertices. These intermediate bank points have their elevations interpolated using the U/S and D/S bank elevations. The 1D and 2D engines use the highest of the bank point elevations and the 2D vertices elevations to set the crest elevation of the weir on each bank segment.The channel banks are plotted as a dashed line on the Plan View. Note that by default an open channel is created with 2 banks, one on each side. The exchange can happen independently on each side/bank, depending on the respective bank and terrain elevations
For the Stormwater Controls, two banks are generated around the SWC outline. The SWC center line shows the direction of the structure and is used for splitting the outline into a left bank and right bank. Otherwise, the approach is fairly similar to that used for the open-channels. The water elevations in the SWC Ponding area (i.e. Surface layer) are used to drive the exchange with the 2D domain.
Note that the area occupied by the channel or the SWC is represented by a void polygon in the 2D domain. The void polygon prevents water from entering its extent. This is done so that water represented by the 1D engine in the channel or the SWC is not double counted in the 2D domain.
Before analysis occurs the phase is validated and the following scenarios are flagged:
These scenarios all generate an error, which does require action before 1D - 1D analysis is allowed to occur:
| Error | Applies to | Correction |
| Channels with inverts set above the surface are not supported for 1D - 2D analysis, please review the design. | Open Connections - Trapezoidal Channel, Rectangular Channel, Triangular Channel or open Custom connection. | Check that any connections for the items in the applied to section do not have invert levels that are above the surface level. |
| Channels with downstream elevation lower than the base of the downstream element elevation cannot be analyzed in 1D/2D. Please review the design. | Open Connections - Trapezoidal Channel, Rectangular Channel, Triangular Channel or open Custom connection. | Check that any connections for the elements in the applied to section do not have downstream elevations lower than the base of the downstream element elevation. |
| Stormwater Control outlines should not overlap and are not supported for 1D - 2D analysis, please review the design. | Linear Exchange Stormwater Controls - Bioretention Area, Porous Paving, Infiltration Trench, Pond and Swale. | Check that outlines for the items in the applied to section do not overlap one another. |
| Connections should not overlap SWC boundaries except to connect to inlets and outlets and are not supported for 1D - 2D analysis, please review the design. |
Open Connections - Trapezoidal Channel, Rectangular Channel, Triangular Channel or open Custom connection that overlap the following Stormwater Controls -Bioretention Area, Porous Paving, Infiltration Trench, Pond and Swale. |
Check that connections do not enter in and out of an Stormwater control outline multiple times. There should only be one entry point, one exit point or for multi-point connections only one section must enter/exit. |
| Connections should not overlap and are not supported for 1D - 2D analysis, please review the design. | Open Connections - Trapezoidal Channel, Rectangular Channel, Triangular Channel or open Custom connection. | Check that any connections for the items in the applied to section do not overlap one another. Multi-point connections may overlap in several locations. |
| Connections should not cross and are not supported for 1D - 2D analysis, please review the design. | Open Connections - Trapezoidal Channel, Rectangular Channel, Triangular Channel or open Custom connection. | Check that any connections for the items in the applied to section do not cross one another. Multi-point connections may cross in several locations. |
These scenarios all generate a warning, which do not require any action:
| Warning | Applies to |
| Stormwater Control omitted from 2D exchange as entirely within another Stormwater Control. | Linear Exchange Stormwater Controls - Bioretention Area, Porous Paving, Infiltration Trench, Pond and Swale |
| Manhole omitted from 2D exchange as within Stormwater Control or Connection. | Manholes only |
| Stormwater Control omitted from 2D exchange as within Stormwater Control or Connection. | Point Exchange Stormwater Controls - Cellular Storage, Chamber, Dry Well, or Tank |
| Manhole excluded from 2D exchange as it is outside of the surface boundary. | Manholes only |
| Connection excluded from 2D exchange as it, or part of the boundary, is outside of the surface boundary. |
Open Channels |
| Stormwater Control excluded from 2D exchange as it, or part of the boundary, is outside of the surface boundary. |
Linear Exchange Stormwater Controls - Bioretention Area, Porous Paving, Infiltration Trench, Pond and Swale Point Exchange Stormwater Controls - Cellular Storage, Chamber, Dry Well, or Tank |
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