Layout for WBNM type storage routing model
A catchment is divided into sub-catchments that depend on junctions of streams and internal ridge lines. Nodes should be placed at the outlets of self-contained sub-catchments - those at the top of the catchment, with no streamflow from upper sub-catchments running through them. Stream reaches are to be placed between the nodes.
Rainfall is converted to rainfall excess at the sub-catchment nodes and non-linear routing occurs at these nodes. It also occurs in the stream routing reaches, with the area of the catchment at the downstream end of a reach being a controlling factor. (This is due to the reach being assumed to travel through the sub-catchment and for routing to be influenced by the sub-catchment size.)
In DRAINS, after selecting a WBNM type storage routing model, you should set out a system with a node near the outlet of each sub-catchment, at junctions of streams and the outlet. Connect these nodes with stream routing reaches. Add sub-catchments to the nodes representing sub-catchments. There are no overflow links, such as those that occur in a pipe system.
Generally, you will want to perform routing in a reach when flows from upstream sub-catchments run through it. If routing reaches are merely used to connect sub-catchment nodes to a junction, they should be given a Stream Lag Factor of 0.0.
Provide information for sub-catchments by opening their pop-up (right mouse button) menu, and selecting edit data to open the following property sheet:
The catchment name and area need to be entered. If the WBNM hydrological model required has different losses to the default model specified in the Storage routing model property sheet, it can be selected from the Hydrological Model buttons.
Within a WBNM-type model, it is only necessary to specify a name for nodes. However, if this model is intended to interface with a Horton (ILSAX) model or open channel links (prismatic, irregular or multi-channel), a surface level must be provided at the connecting node.
For the stream routing reaches, the following property sheet will appear:
The reach name and a stream lag factor are required. Indicative values of the latter are shown below:
The WBNM model can be linked to drainage system components including pipes, open channels and sub-catchments employing the ILSAX hydrological model. It cannot be intermixed with other types of storage routing model.
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