Designing a Site Drainage System
The Drainage mode provides a dedicated toolbar for laying out a complete drainage plan — from surface inlets through underground pipes and catch basins to a final outlet point.
Designing a Site Drainage SystemThe drainage sections of the Water tab cover surface collection (Drain Inlet, Channel, Downspout), conveyance and discharge (Drain Pipe, Outlet), and access and maintenance (Catch Basin, Cleanout). A drainage plan follows runoff: water enters at inlets, runs through buried pipes, gathers at collection points, and leaves at an outlet. Place each object from the Water tab, then connect them with drain pipe runs and edit each object's properties in the Inspector.
Place drain inlets at low points
Select the Place Drain tool and click on the canvas at each location that needs to collect surface water — typically patio corners, lawn low points, and the base of slopes. Each inlet can be a point drain (circular yard drain) or a trench drain (linear channel with configurable length and angle). Set the type in the Inspector after placing.
Place catch basins where pipes converge
Use the Place Catch Basin tool to add a below-grade collection box at points where multiple drain pipes meet or where a change in pipe direction requires a transition chamber. Place the catch basin at the lowest accessible point in the drainage network. A single basin can accept multiple incoming drain pipes and route water into one outgoing pipe.
Draw drain pipes connecting inlets to the basin
Select the Draw Pipe tool. Click to start a pipe run at a drain inlet, add waypoints by clicking, and double-click or press Enter to finish at the catch basin or outlet. Pipe endpoints snap to nearby inlets, basins, and outlets. Set pipe diameter in the Inspector — common sizes are 100 mm, 150 mm, and 200 mm. Buried pipes render as dashed lines on the 2D plan.
Place the outlet and connect the outgoing pipe
Use the Place Outlet tool to add a discharge point at the end of the drainage network. Choose the outlet type in the Inspector: toStreet (storm drain connection), toSoakaway (subsurface infiltration pit), or toGardenEdge (daylighting at the site boundary). Draw a drain pipe from the catch basin to the outlet to complete the network.
Set burial depths and annotate
Select each pipe and component and use the Inspector to set the burial mode and depth. The default pipe burial depth is 300 mm. Components can also be set to on-surface or above-ground modes. Use the Annotate tool to label pipe diameters, invert levels, and flow directions. Buried pipes are shown as dashed lines; surface components use solid outlines.
Set burial and slope
Select each drain pipe and open its Burial section in the Inspector. Set the burial Mode (On Surface, Buried, or Inset) and, when buried, the Depth. For a falling run, open the Slope section, enable slope, and set the Start Depth and End Depth so the pipe drains toward the outlet.
Work from the outlet back toward the inlets when planning pipe routes. Knowing where water exits first makes it easier to route pipes along the shortest path with consistent fall.
The Water tab is a schematic planning aid — verify the drainage design with a qualified professional. It does not simulate real-world flow or hydraulic capacity.
Frequently Asked Questions
What's the difference between a drain inlet and a catch basin?
A drain inlet collects surface water at a single point; choose Point Drain or Grate Drain as its Inlet Type. A catch basin is a below-grade chamber where multiple pipes meet before routing onward; it carries a fixture style and a basin depth.
How do I set how deep a drain pipe is buried?
Select the drain pipe and open the Burial section in the Inspector. Set the Mode to Buried and adjust the Depth. For a falling run, open the Slope section and set separate Start and End depths.
Which drainage objects are available?
Surface Collection: Drain Inlet, Channel, Downspout. Conveyance & Discharge: Drain Pipe, Outlet. Access & Maintenance: Catch Basin, Cleanout. Each is a dedicated object with its own Inspector fields.