Flowpath Engineering Portal

Stormwater Catchpit Network Pipe Sizing — NZ Design Tool

Design branching stormwater networks, size pipes up to 1200 mm, and draw interactive long sections with approximate water levels, losses and preliminary manhole sizes.

Try this calculator free About Flowpath Engineering

What this tool does

Rational Method Flow Calculation

Calculate stormwater runoff using Q = C × I × A with automatic flow accumulation through branching pipe networks.

Colebrook-White Pipe Sizing

Select pipes up to 1200 mm using Darcy–Weisbach and Colebrook friction, with a 70% normal-depth sizing limit.

Interactive Long Sections

Choose start and end nodes to show connected pipes, preliminary manholes, assumed ground and approximate water levels. Export SVGs or print to PDF.

Water Levels & Estimated Losses

Include tailwater, pipe friction and preliminary chamber losses. Review surcharge separately from the normal-depth pipe sizing check.

Ready to run your calculations?

Sign in for full access or continue as a guest -- no account required.

Open Catchpit Network Designer

Part of the Flowpath Engineering suite of free civil engineering tools for New Zealand.