Source allows the user to create the catchment model though Geographic Wizard conveniently. However, before Source version 4.10.0 - Beta Release (August 2019), the user cannot change the created sub-catchment boundary such as merge sub-catchment after Geographic Wizard creates the scenario.  The new function was developed to merging sub-catchments and reset relevant model elements (such as network/link) and attributes (such as rainfall runoff model parameters) in an existing catchment catchment model. The developed function has been included in the Source software tool after the version 4.10.0 – Beta Release.

There are two methods developed for combining sub-catchments: (a) at selected node boundaries and (b) from selected catchments.  Both methods are described below in this page.

First of all, the user needs a Source project with any geographic scenario and open the project.

Combine Catchments At Selected Node Boundaries:

This method allows the user to combine all catchments upstream of the selected node such as a confluence in a catchment model.

The procedure to combine catchments at selected node boundaries is illustrated as follows:

• Click on a single node from the interface to select this node, such as the confluence orange cycled on Figure 1 ( Node on catchment SC#10 in this example)

Figure 1. Selected the node to start combine sub-catchments function

• Right click on the interface’s empty space (that can keep the node selected) to pop up the Geographic Editor.
• Click on Combine Catchments >> At selected node boundaries to display the windows of Combine Catchments as Figure 2. At the beginning, the contests under Catchment Group is empty.

Figure 2.  Combine Catchments Windows Interface

• Click on the button of Find catchment groups at boundaries to display all sub-catchments upstream of the selected node (i.e. Node on catchment SC#10 in this example) in Catchment Groups (shown as Figure 3).

Figure 3.  Combine Catchments at selected node with all found upstream sub-catchments

Some functions on Figure 3 are given below:

• To Primary catchment: The property of this sub-catchment will be retained for the combined catchment such as the property: the parameters of rainfall runoff and other models. In this example, primary catchment is SC#13. This node is single outlet of the combined catchment.
• Absorbing Catchments: Sub-catchment listed under Catchment (i.e. SC #21, SC #12, SC #20 in this example) will be merged with SC #13 and their properties will be discarded.
• Assign primary: This button allows the user to change the primary catchment if the user wants to use the property from another sub-catchment for the combined catchment. The user can click on any sub-catchments listed under Catchment, then click on Assign primary The selected sub-catchment (SC #12 in this example) will be displayed into Primary catchment, and previous primary catchment will be moved to the absorbing catchments.
• Network Restructure:

         Collapse to primary catchment node – Ticking this function will lead a network with one link from the primary catchment to the outlet. Otherwise, the networks and nodes from all absorbed catchments will be kept as it is.

         Absorb upstream boundary nodes- This function allows to remove all nodes in absorb catchments and it is enabled only when Collapse to primary catchment is ticked. 

• Combine button will close Combine Catchments Interface; combine the upstream catchments and reset the network and nodes accordingly.
• Cancel button will close Combine Catchments Interface without any combination action.

Combine catchment from selected catchments:

This method allows the user manually to select the sub-catchments to combine.

The procedure to combine catchments from manually selected sub-catchments is shown below:

• Manually select the sub-catchments to combine (use the Zoom option to Zoom in to the sub-catchments, and keep Selected Catchment in Layer Manager ticked) as Figure 4

Figure 4.  Manually select sub-catchments for combining catchments 

• The first catchment selected is deemed to be the Primary Catchment.
• Right click on the interface to pop up the Geographic Editor as Figure 5

Figure 5. start combine sub-catchments function from manually select sub-catchments  

• Click on Combine Catchments >> From selected catchments to pop up the Windows of Combine Catchments as Figure 6.

Figure 6.  Combine Catchments Windows Interface for manually select sub-catchments

• The elements’ functions on Figure 6 can refer to those on Figure 3 and explained before
• Click on the Combine button on Figure 6 will lead a catchment combined from 4 catchments shown in Figure 7

Figure 7.  The results catchment combined from manually selected sub-catchments

• The associated properties  are changed. For example, the new rainfall and runoff table  (Figure 8) shows the sub-catchments #12, #SC 20 and #21 was removed, and the combined catchments inherited the property from SC# 13, primary catchment.

Figure 8.  The results catchment combined from manually selected sub-catchments

• Save the Source project to keep the combined results

Note that

• The change of combined sub-catchments is unable to reverse

• At the moment, the use needs to have a single  outlet for all of the sub-catchments you are combining. The Source will relax this restriction in future versions.