Civil 3D Catchments

Use this skill when working with catchment areas, flow paths, watershed delineation, or drainage analysis in Civil 3D.

Catchment Overview

Catchments in Civil 3D represent drainage areas on a surface where water flows to a common discharge point. They are fundamental to stormwater and hydrology analysis, linking surface terrain data to pipe network design. Each catchment is defined by a boundary polygon, a reference surface, and a discharge point where collected runoff exits the catchment area.

Catchments are typically derived from surface analysis (watershed delineation) or created manually by drawing boundaries. They store hydrological properties such as area, runoff coefficient, rainfall intensity, and time of concentration for use in the rational method and other drainage calculations.

The .NET API for catchments is more limited than the interactive UI. Many creation and analysis operations must be performed through commands rather than direct API calls.

Accessing Catchments

CivilDocument and the Catchment Collection

Catchments are accessed through CivilDocument and its site collections. Catchments belong to a Site, which groups related drainage objects.