Inference Rules - Conduit Parameters

Missing data values can be inferred from existing data, allowing gaps in data to be filled in with reasonable values.

Inference data is edited on the Inference Data Editor.

The following can be inferred for conduits:

Parameter	Inferred From
Size and Shape	Height, Width and Shape can be inferred from upstream and downstream conduits. Shape will only be inferred if the Infer Shape parameter is checked in the Inference Editor. See Size and Shape section below for more details.
Upstream / Downstream Invert Level	There are four methods by which invert level can be inferred: Invert from Invert Level Conduit US Invert Level and DS Invert Level values are inferred from connected conduit Invert Level values: US / DS Invert Level = Lowest Invert of connected conduits See Invert from Invert Level section below for more details. Invert from Soffit Level Conduit US Invert Level and DS Invert Level values are inferred from the soffit level of conduits connected to the node at which the conduit invert level is missing. US /DS Invert Level = Lowest Soffit of connected conduits - Height of selected conduit See Invert from Soffit Level section below for more details. Invert from Gradients Conduit US Invert Level and DS Invert Level values, for a conduit with one missing invert level, are inferred from the conduit's known invert level and the shallowest gradient of connecting conduits. US Invert Level = DS Invert Level + ΔH DS Invert Level = US Invert Level - ΔH Where ΔH = Shallowest gradient of connected conduits multiplied by length of conduit to be inferred. See the Invert from Gradients section below for further details. Invert Interpolate from Inverts The invert level of a conduit is inferred by linear interpolation between known upstream and downstream inverts. See the Interpolate from Inverts section below for further details.
Headloss Type and Coefficient	Headloss Type and Coefficient and inferred by calculating the intersection angle of the conduit to determine the appropriate headloss coefficient. See the Conduit Headloss Type and Coefficient section below for further details.

Size and Shape

Height, Width and Shape can be inferred from upstream and downstream conduits. Shape will only be inferred if the Infer Shape parameter is checked in the Inference Data Editor.

When inferring values for a particular conduit, the system searches for valid conduit values upstream and downstream of the conduit.

The following rules are applied for each conduit with missing size or shape:

1. If conduit shape is being inferred and is missing, the system searches for valid values in the following order:
   • upstream as far as the first upstream junction
   • downstream as far as the first downstream junction
   • upstream above the upstream junction
   • downstream below the downstream junction
   • If no values are found, inference will not be carried out.
2. Missing widths will be calculated if the conduit has a valid shape and height and the shape has a formula.
   • CIRC, OEGB and OEGN shapes - width equals height
   • EGG and EGG2 shapes - width equals two-thirds of the height
   • All other shapes - width cannot be calculated as a formula for the calculation of the width is not available
3. If the width cannot be calculated, it is inferred as follows:
   1. The system searches as far as the upstream junction and uses the first valid width found.
   2. If no width is found, the search continues in any conduits immediately upstream of the junction. The largest width of conduits connected to the junction is stored.
   3. The system searches as far as the downstream junction. If a valid width is found, the system uses the larger of that width and any upstream width stored at step (b).
   4. If the width is still missing, the system uses the upstream width stored at step (b), if any.
   5. If the width is still missing, the system searches any conduits immediately downstream of the downstream junction and uses the smallest width found.
4. If the width has been inferred and the shape is missing (and being inferred), the system applies the shape of the conduit that was used for inferring the width.

These rules are applied to each conduit with missing size or shape values.

The whole process is iterated until either no further sizes can be inferred or 50 iterations have been completed.

Invert from Invert Level

Missing conduit Invert Level values are inferred from the invert level of conduits connected to the node at which the conduit invert level is missing.

InfoWorks ICM assumes that the conduit invert level at a node is the same height as the known invert level. This may lead to backdrops. Use the Invert Interpolate from Inverts rule to avoid backdrops (inverts will be assumed level at each node).

Check the Infer invert levels equal to zero option to apply inference to invert levels with zero value in addition to missing invert levels. (In certain locations an invert level of zero may be valid.)

Check the Use chamber floors if required option, to infer invert level from Chamber Floor level if the invert level cannot be inferred using this method.

Tip: When inferring invert values for a selection, select the Node attached to the conduit for which the value is to be inferred.

For each (selected) node in the network:

1. If a conduit invert is missing, find the lowest invert level of all connected conduits at the selected node.
2. Invert level of conduit is calculated as:
   • Invert Level = Lowest Invert Level of connected conduits
3. Check that the upstream invert is higher than the downstream invert for the selected conduit.
4. If the invert cannot be calculated and the Use chamber floors if required option is checked, the invert will be set equal to the chamber floor.
5. If the Use chamber floors if required option is checked, use the chamber floor value is lower than the calculated invert.

Invert from Soffit Level

Missing conduit Invert Level values are inferred from the lowest soffit level of conduits connected to the node at which the conduit invert level is missing. InfoWorks ICM assumes that the conduit soffit level at a node is the same height as the known soffit level. This may lead to backdrops. Use the Invert Interpolate from Inverts rule to avoid backdrops (inverts will be assumed level at each node).

Check the Infer invert levels equal to zero option to apply inference to invert levels with zero value in addition to missing invert levels. (In certain locations an invert level of zero may be valid.)

Check the Use chamber floors if required option, to infer invert level from Chamber Floor level if the invert level cannot be inferred using this method.

Tip: When inferring invert values for a selection, select the Node attached to the conduit for which the value is to be inferred.

For each (selected) node in the network:

1. If a conduit invert is missing, calculate the soffit level of all connected conduits at the selected node.
   • Soffit Level = US Invert Level + Cross Section Height
2. The lowest Soffit Level of all connected downstream conduits is determined from Step 1.
3. For conduits connected to the node with a missing invert level and known Height, the invert level is calculated as:
   • Invert Level = Lowest Soffit Level - selected conduit Height
4. Check that the upstream invert is higher than the downstream invert for the selected conduit.
5. If the invert cannot be calculated and the Use chamber floors if required option is checked, the invert will be set equal to the chamber floor.
6. If the Use chamber floors if required option is checked, use the chamber floor value is lower than the calculated invert.

Invert from Gradients

Conduit US Invert Level and DS Invert Level values, for a conduit with one missing invert level, are inferred from the conduit's known invert level and the shallowest gradient of connecting conduits.

Check the Infer invert levels equal to zero option to apply inference to invert levels with zero value in addition to missing invert levels. (In certain locations an invert level of zero may be valid.)

For a conduit with either the US Invert Level or the DS Invert Level missing, and a valid Height and Length (i.e. greater than zero):

1. A search is made for conduits connected to the other side of the node at which the conduit invert level is missing.
2. The gradients for connected conduits found in Step 1 are calculated from:

   

   For gradients to be calculated, conduits must have:

   • Known US Invert Level and DS Invert Level
   • Length > 0
   • Length < Maximum Conduit Length (specified in Inference Editor)
3. The shallowest gradient calculated in Step 2 is determined:

   For a gradient to be used in inference the following criteria must be satisfied:

   • Gradient > 0
   • Gradient < Maximum Conduit Gradient (specified in Inference Editor)
4. The difference between US and DS invert levels of the conduit with the missing invert level is calculated as:

ΔH = Shallowest gradient determined in Step 3 x Conduit Length

5. Missing invert levels are calculated as:
   • US Invert Level = DS Invert Level + ΔH (Step 4)
   • DS Invert Level = US Invert Level - ΔH (Step 4)
6. The soffit level of the conduit at the inferred invert is calculated:
   • Inferred invert + US/DS Height

If the calculated soffit level is greater than the Ground Level at the conduit's connecting node, inference will not be carried out.

7. If no gradient has been found then attempt to find a gradient at the conduit's non-missing invert level end by repeating steps 2 to 6.

Invert Interpolate from Inverts

The invert level at a conduit is inferred from the invert levels of connected upstream and downstream conduits:

• If there are connected conduits with known invert levels at the location of the invert to be inferred, the unknown invert level is inferred directly from a connected conduit invert.
• If the invert levels of connected conduits at the location of the invert to be inferred are unknown, the unknown invert level is inferred by linear interpolation between known upstream and downstream inverts.

Check the Infer invert levels equal to zero option to apply inference to invert levels with zero value in addition to missing invert levels. (In certain locations an invert level of zero may be valid.)

Direct Inference from Connected Conduit Invert

If there is a single connected conduit with known invert level at the location of the invert to be inferred, the invert level at the connected end of the conduit will be used.

If there are multiple connected conduits with known invert levels at the location of the invert to be inferred; the invert level at the connected end of the shortest conduit is used.

Click on the image below to show the example.

Example

Inference by Linear Interpolation

The invert level of a conduit is inferred by linear interpolation between known upstream and downstream inverts:

• Step 1: For each conduit with missing invert levels, the system searches upstream and downstream for the closest known upstream and downstream invert levels (including invert levels of the conduit for which values are being inferred).
  • If there are multiple known invert levels at the same distance, the lowest value is taken.
  • If there is a current selection of conduits, invert levels of selected conduits will be used in preference to invert levels of non-selected conduits.
• Step 2: Missing invert levels are calculated using linear interpolation between the known upstream and downstream invert levels found in Step 1.

Click on the image below to show the example.

Example

• A run of conduits A-D has unknown invert levels at B and C.
• Conduit AB is selected for inference
• The Interpolate from Inverts rule searches upstream and downstream to find the known inverts:
  • US Invert Level of conduit AB
  • DS Invert level of conduit CD
• The DS Invert Level of conduit AB is calculated as:

  D + [x *(D-A)]/L where: D = DS Invert Level of conduit CD A = US Invert Level of conduit AB x = Distance from downstream node of conduit AB to node D L = Total Length from node A to node D

Headloss Type and Coefficient

Conduit headloss type and headloss coefficient can be inferred for any conduit where these values are missing by selecting the appropriate option on the Inference Data Editor.

Check the Infer headloss with default flags (#D) option to apply inference to values for which the data flag is #D in addition to missing values.

The following rules are applied for each conduit where the upstream headloss coefficient is missing or (if specified) has a default value:

1. The intersection angle is calculated as follows:
   • If the conduit is connected to a node that is not a junction (for instance it has only one downstream and one upstream conduit), there is only one intersection angle to calculate. This is the angle between the upstream conduit and the line that would be taken by the downstream conduit if it continued upstream.
   • If the conduit is connected to a node that is a junction, the maximum intersection angle to the major upstream conduit is calculated. The major conduit is defined as the upstream conduit with the largest width. If more than two upstream conduits are found they must have the same shape, otherwise no major conduits can be found and no valid intersection angle can be calculated. If more than two conduits are defined as major conduits the intersection angle is calculated for each one and the maximum angle is used.
2. If a valid intersection angle is found the headloss coefficient is calculated by linear interpolation using the table below.
3. If a valid headloss coefficient is calculated, this value is applied to the upstream headloss for the conduit and the headloss type is set to Normal. Otherwise, if the headloss coefficient does not have the default value, the headloss type is set to None.
4. If the headloss type is missing and there is a valid headloss coefficient, the headloss type is set to Normal. Otherwise, the headloss type is set to None.
5. These steps are repeated for downstream headloss, the major conduits defining the intersection angle now being located downstream.

These rules are applied to each conduit with missing data. No iteration is required for this method.

The following table is used when interpolating the headloss coefficient from the intersection angle:

Angle (degrees)	Coefficient
0	1.0
15	2.15
30	3.3
60	6.0
90	6.6
> 90	8.0