Workflow: To Set Up a Catchment Model and Pipe Network

The first step in setting up a catchment model is to determine the general drainage trends across the site. This means identifying high points (hydraulically most distant points), low points (collection or discharge points), as well as channels and ditches. Low points are often a wetland or pond on the site, or abutting property, or could be a catchbasin in an adjacent road.

After this initial analysis is done, you can use the catchment, flow path, and flow segment creation commands to create the catchment data.

To analyze a site's drainage patterns, use the Surface Properties command to do a level analysis, watershed analysis, and/or a slope arrow analysis and/or Use the Water Drop command to show where the water would flow across the surface	You can do multiple Surface Properties analyses, and then draw polylines around the areas that represent the catchments you want to analyze.
Optional: Based on a likely discharge point, create a pipe network with an outfall structure at that location	This step is not required in order to create a catchment, but an association with a structure is required if you want to use the catchment and flow path data in Autodesk Storm and Sanitary Analysis.
Create a catchment group	Catchment groups allow for the organization of catchments, such as catchments that may pertain to a single pipe network or a pre-condition analysis.
Create a catchment from a surface or Create a catchment from a polyline	Use the Create Catchment from Surface command for an area that is contained within the surface. If you are defining an area that flows to a boundary, you may need to draw a polyline around the desired analysis area and use the Create Catchment from Object command (such as if it abuts an adjoining property or wetland).
Create a flow path from a surface or Create a flow path from a polyline	You can create the flow path while using the catchment creation commands, or you can create or edit the flow paths after creating catchments.
Define the outfall reference structure	When creating the catchment, you can select the pipe network structure you created in Step 2 above, or you can define this later in the Catchment Properties.
Create additional flow segments and define segment data	The end result is a calculated Time of Concentration (Tc) which can then be used, along with the catchment area, runoff coefficient, and pipe structure outlet data, in Storm and Sanitary Analysis.