Which step is first in the design process of a culvert?

In the design process of a culvert, determining the diameter is the first critical step because it establishes the culvert's size and directly relates to its ability to convey water flow effectively. The diameter must be adequate to handle the expected flow, preventing overflow or flooding in the surrounding areas.

Starting with the diameter allows engineers to set appropriate design parameters and influences subsequent calculations, including headwater depth and exit velocity. Once the diameter is established, other factors such as flow rates, material selection, and culvert length can be accurately assessed, ensuring the structure meets both hydraulic and structural requirements.