# What elements can subcatchments “drain to” in InfoWorks ICM?

Have you wonder where subcatchments can “drain to” in InfoWorks ICM? Probably you are thinking nodes, but the correct answer is more complex giving the flexibility InfoWorks ICM offers you. Let’s have a look:

• Nodes: subcatchments can drain to any node type, except outfalls. For example, subcatchments can discharge runoff to a manhole in sewer systems or to break nodes in river reaches. If manholes have flood type “Inlet” or “Gully”, subcatchments with a system type of ‘storm’, ‘combined’ or ‘overland’ drain to the above ground elements and are subject to the inlet parameters before they can enter the below ground element, whereas subcatchments with ‘foul’, ‘sanitary’ or ‘other’ system types drain directly to the below ground element.
• Links: subcatchments can drain to any link. For conduits, river reaches, channels and bridges the runoff from subcatchments is applied as lateral inflow. For control links, the runoff is applied to the upstream node. If this node is an outfall, the downstream node is selected to drain to, and if both nodes are outfalls the runoff is lost.
• Multiple Links: similar conditions to links, but in this case subcatchments drain to several links according to a weight factor. The weight factor can be user-defined or dependent on the link length.
• Subcatchments: subcatchments can drain to another subcatchment and the runoff generated by the first one is added to the rainfall of the destination one. The runoff is then subject to the initial loss, volume, and routing models of the surfaces of the destination subcatchment.
• 2D zone: subcatchments can also drain to 2D zones if they discharge to a dummy 2D manhole node. A 2D manhole with small volume can be defined as dummy node to make the connection between the subcatchments in the 1D model with the 2D zone in the 2D model. The dummy node needs to be connected to a link, which can be a flap valve in the opposite direction.

In conclusion, the correct answer is actually almost all model 1D objects: Nodes, Links, and Subcatchments (Figure 1). Each of these objects include more options to make the “drain to” very flexible and customisable according to your real case. In addition, you can use a representation based on these 1D objects to enable the subcatchments to drain directly to the 2D model.

Figure 1. Examples of Subcatchments “drain to” options available in InfoWorks ICM: nodes (grey), links (orange), multiple links (red) and subcatchments (green).