Storm Tabulations (Hydraulic Grade Line / Velocity)

Stormwater Rational Method & Manning’s Pipe Capacity Calculator

This Excel tool simplifies stormwater pipe design using two trusted civil engineering methods:

• Rational Method – to estimate peak runoff based on basin area, runoff coefficients, and rainfall intensity.
• Manning’s Equation – to calculate flow capacity, velocity, and hydraulic radius for circular pipes under full-flow conditions.

Key Features

✅ Calculates peak runoff (Q = CiA) with customizable rainfall intensity and weighted C-factors

✅ Calculates Hydraulic Grade Line and velocity within the pipes

✅ Built-in formatting for easy QA and submittals

What’s Included

• Excel file preloaded with sample structures, basins, and pipe data
• Editable rainfall intensity, tailwater elevation, and Manning’s n
• Auto-calculated flow, capacity, and velocity columns

🔐 Note:

This spreadsheet was developed independently and does not reference any proprietary tools. It is intended for educational and professional reference only.

Disclaimer:

This tool was developed independently using general engineering knowledge, public-domain formulas, and personal experience. It does not use or reference any proprietary materials or confidential resources. Use of this spreadsheet is at the discretion of the user, who is responsible for verifying all calculations and assumptions. It does not guarantee accurate results.