Tech Tips


Adding Subcatchments

This Tech Tip explains how to graphically enter the subcatchments for stormwater design.
 

TechTips


This function allows you to create subcatchment runoff areas by defining the area graphically by drawing a polygon and giving it an identifying name. The program will save all the vertex coordinates together with the subcatchment name. The subcatchment can then be linked to a specific Node record of which the runoff area will be updated to the calculated size of the subcatchment. The drainage path can be indicated graphically and the drainage length and a weighted average slope will be calculated and entered into the Runoff time calculation. The subcatchment can also be displayed graphically by specifying the subcatchment settings in the Display settings. If you have deleted records, they appear in the Node Data dialog in grey scale.

In this example, we will be creating a Subcatchment that will drain to node 70.


Adding the Subcatchment

Stormwater Mode, Graphical Menu Add Subcatchment

The program will prompt:



Enter a name for the subcatchment, and then click on the tick to continue.Enter a name for the subcatchment, and then click on the tick to continue.



The next step is to indicate the subcatchment perimeter.



Indicate the start point and then click on the various corner points to define the subcatchment.



As you indicate the area of the subcatchment, the edges will be highlighted.



After defining the shape, right click, and then select Close Subcatcment, the subcatchment will then be closed.



Once the subcatcment has been closed, you will be prompted to indicate the node the subcatchment must drain to.



Indicate the node, you will then be prompted if this is the correct node. Click Yes if the node selected is correct, if not then click No.



The mouse cursor will now be locked to the draining node, and you must now define the paved drainage path. Once this has been defined, Right click to end.



You can then End the drainage path, or define a grassed path if required.



Once the path has been defined, you need to confirm if the path is correct. If not you can modify the path.

The runoff time calculator dialogs will open according to the specified runoff calculation method.


Illudas Method

The Paved Area Entry Time Calculator dialog will open with the Length and Slope entered as calculated from the defined drainage path.



Click on OK and the Grassed Area Entry Time Calculator dialog will open with the Length and Slope entered as calculated from the defined drainage path. Enter the Manning Factor and adjust the Length and Slope if required.



Enter the required Manning Factor , then click on OK. The Runoff page for node 70 will open with Subcatchment 70 selected and the Paved and Grassed Entry Time updated.



Click on Close.


Rational Method

The Time of Concentration dialog will open with the Longest Length and Average Slope entered as calculated from the defined drainage path. Enter the Flow Type and the Roughness Coefficient and adjust the Length and Slope if required.



Click on OK. The Runoff page for node 70 will open with Subcatchment 70 selected and the Time of Concentration updated.



Click on Close.


Wallingford Rational Method

The Wallingford Time of Entry dialog will open with the Overland Flow Length and Slope entered as calculated from the defined drainage path.



Click on OK. The Runoff page for node 70 will open with Subcatchment 70 selected and the Time of Concentration updated.



Click on Close.

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