Rainfall-runoff in InfoWorks ICM: Traditional Subcatchment Hydrology

InfoWorks ICM is a powerful hydrologic and hydraulic modeling tool. As its name suggests, ICM – Integrated Catchment Modelling, InfoWorks ICM is capable of simulating 1D network and 2D surface as well as hydrology and hydraulics in one single model. In infoWorks, to model a rainfall-runoff process two options are available: this post is focusing on the first method and a second post covers the topic of Rain-on-Grid.

• Traditional subcatchment hydrology
• Rain-on-Grid on 2D zone

Similar to other node-link H&H modeling tools, subcatchments (subbasins, drainage areas) need to be delineated/defined and the runoff flows are to be routed to subcatchment outlets (nodes, links, or others) after accounting for various losses. InfoWorks ICM subcatchment hydrology includes most of the common methods for evaporation, initial loss, runoff volume, and routing (Table 1).

Most of the hydrology parameters need to be provided under subcatchment, land use, runoff surface property editors or the subcatchment grid windows in InfoWorks (Figure 1 and Figure 2).

Attention should be paid to rainfall event editor, where hyetographs resides. In addition to rainfall intensity and evaporation data, initial condition data can also be typed into rainfall event editor (Figure 3). In fact, InfoWorks makes things so complicated and confusing that initial condition data can be entered at five different places in rainfall event editor alone, no mention other locations such as subcatchment runoff surface editor.

Per InfoWorks Help Files, the order of precedence for applying initial runoff conditions to subcatchments in rainfall event editor is as follows:

• initial conditions specified on the Runoff Subcatchment, Units Subcatchment or ReFH Subcatchment tab pages
• initial conditions defined on the Runoff Surface tab page
• initial conditions defined on Globals tab page
• initial conditions defined in the Rainfall Profile Properties of a rainfall profile
• initial conditions defined in the Rainfall Sub-Event Properties of a rainfall sub-event

To avoid any confusion, it is strongly suggested that initial condition data be solely provided in subcatchment runoff surface property editor, unless the rainfall event editor is the only place for an initial condition parameter to go.

In Figure 4, the subcatchment rainfall profile is set as “1”. When running the model, the rainfall event needs to have a profile with exactly the same name of “1”; otherwise, the run will apply the first event from the left of the rainfall event editor table. In the example rainfall event editor table in Figure 5, since no rainfall profile is named as “1”, the model run will use the rainfall profile of “rainfall_5-yr”.