Talking about infiltration in ICM can either mean infiltration of liquid (effectively rainwater) into either the ground water, or into our sewer pipes. In a way, there are one of the same, as for water to infiltrate our sewers, they effectively need to infiltrate into the ground first. However, in some cases we can apply infiltration directly to the sewers, and in other cases we are applying infiltration to the ground, where it then impacts flow in our sewers as it is again, infiltrating into our network.
1. Applying Infiltration as an Infiltration File to our ground (soil)
Generally, when building a model, we apply infiltration to our ground / soil at each sub-catchment level. So when we create a subcatchment, we can apply infiltration through Ground Infiltration Values. We can create a number of Ground Infiltration Values (or Ground Infiltrations IDs) and apply them to various subcatchment. If we are happy that the ground has a appropriately similar infiltration value, we can apply the same infiltration ID across our entire model. Or if the soil varies significantly at parts of the catchment, we can create different infiltration IDs. IDs can be created via the subcatchment table interface, in the Ground Infiltration Tab. You must add a unique Ground Infiltration ID and can then at properties relating to the Ground Infiltration.
The InfoWorks ICM help lists the following help text for each field name associated with the infiltration file.
Ground Infiltration file information can also be viewed and edited through the Subcatchment dialogue box
2. Applying Infiltration as Baseflow (to sewers)
We can apply infiltration (in addition to any already applied via the infiltration file) as base flow (m3/s) to pipes directly and via the Subcatchment table. This can be standard when adding new developments to an existing model, and is sometimes specified by water companies to developers when trying to assess the impact of a new development on the existing system. It can be applied via the Subcatchment dialogue box.
3. Applying Infiltration as subcatchments directly to the sewer link
If a specific source of infiltration has been identified at a point in the sewer system, this can also be added as a dummy subcatchment draining to that point in the sewer. The subcatchment can drain to the entire link or can drain to a dummy node or breakpoint in the sewer. The dummy subcatchment should contain zero contributing area, and flow can be represented in the dummy subcatchment as baseflow.
4. Infiltration from the the ICM Ground Infiltration Model
The ground infiltration Model in ICM can be used represent slow response infiltration of catchments into the sewer system. It is more applicable to longer duration storm events.
The Ground Infiltration model has two components: the soil store and the ground store. In many cases using both components is not carried out and the soil component is used. Different water companies and models can model the ground infiltration differently.
5. Other ways to add Infiltration
There are other ways to model which is effectively just flows entering a sewer system. This can be complicated if the level of infiltration flow varies for a reason (i.e. – tidal) and in these cases, specific level types (such as a tidal level file) may be required. Whatever, method you use, if it is not a conventional standard one, it should be documented and agreed in advance.