Understanding 1D urban drainage models

The basic principles of building 1D urban drainage models in InfoWorks ICM revolve around creating wastewater or surface water sewer networks with flows predominantly driven from urbanized areas.

One or more time-varying inputs can be specified for use as a boundary condition for hydraulic calculations. You can apply these boundary conditions directly or convert the input data into an acceptable hydraulic boundary condition.

Subcatchments, nodes, and links objects are simulated in a basic 1D drainage model and have properties that can be set in ICM.

• Subcatchments are polygons, which represent the physical area from which a system collects water. Subcatchment parameters detail how an event is applied to a node or link.

• Nodes represent a specific point in the network where inflows from subcatchments or from inflow events are assigned. The node types supported for InfoWorks networks include Manhole, Outfall, Break, Storage, and Pond. If you are undertaking 2D modeling, you also have Outfall 2D or Connect 2D.

• Links represent structures that connect nodes. In the InfoWorks network, each node must be connected by a link to at least one other node. One of the nodes must be specified as the upstream end.

Your urban drainage model of subcatchments, nodes, and links helps simulate rainfall-runoff events. In ICM, there are several runoff volume models that you can configure for your needs.

There are many ways that you can quickly and efficiently build or update a model network. If you have existing model data outside of ICM, you can import it directly into a network by importing from CSV or using the Open Data Import Centre (ODIC). You can also manually add subcatchments, nodes, links, or other elements to your model network.

There are also several built-in tools to help you build and update your urban drainage model:

1. Define Branches: Divides the network into long sections by setting the Branch ID field of link objects.
2. Inference: Infer missing network values from existing data, allowing gaps in data to be filled with reasonable values.
3. Population Data: Import subcatchment population data from a GIS layer containing address point, seed point, or census data.
4. Area Take Off: Automate the distribution of runoff surface areas from an Impermeable Area Survey (IAS).
5. SQL: Quickly update and manipulate network data. Save SQL queries for future use to build up a library of commonly used query tasks.