What’s on the Rational Method poster
The rule, 3 worked examples, and the mistake everyone makes.
- For a small catchment, peak runoff is rainfall intensity times area times a runoff co…
- Q = CiA/360 · i in mm/h · A in hectares
- C 0.9, i 50, A 2 ha = Q = 0.25 m³/s
- Roofs and roads = C = 0.7 to 0.95
- Grass over sand = C = 0.1 to 0.3
- Common mistake: Using it on a large catchment → Keep it small and mostly urban
Educational reference. Drainage design follows the sewerage or highway authority's method and its return period rules.
Questions about the Rational Method poster
- What’s on the Rational Method poster?
- The rule, 3 worked examples, and the mistake everyone makes. For a small catchment, peak runoff is rainfall intensity times area times a runoff co…; Q = CiA/360 · i in mm/h · A in hectares; C 0.9, i 50, A 2 ha = Q = 0.25 m³/s; Roofs and roads = C = 0.7 to 0.95; Grass over sand = C = 0.1 to 0.3; Common mistake: Using it on a large catchment → Keep it small and mostly urban. Educational reference. Drainage design follows the sewerage or highway authority's method and its return period rules.
- Who is the Rational Method poster for?
- Rational Method belongs to the Civil Engineering section rather than to a school year, because engineering is not something one grade owns. Anyone learning water resources can pin it up — a beginner, a student mid-course, or someone revising years later.
- When should you use the Rational Method poster?
- Sizing a gully connection, a small drain or a site outfall. A wall chart earns its place by being glanceable from where the work is happening, so Rational Method belongs on the wall where that engineering work actually happens, within glancing distance, rather than filed away.
- What other posters go with Rational Method?
- Culvert Design, Continuity & Energy and Groundwater & Wells sit alongside Rational Method in the Civil Engineering section. Printed together they make a wall rather than a single sheet, which is how a reference set actually gets used.Culvert DesignContinuity & EnergyGroundwater & Wells
- Is the Rational Method poster free to download and print?
- Yes. Rational Method downloads as a free PDF with no account, no email and no watermark, like everything else in the Civil Engineering section. Print as many copies as you like for a home, a classroom, a library or a tutoring group; reselling the file is the only thing the licence rules out.Read the licence
- What size does the Rational Method poster print at?
- Rational Method is a vector PDF laid out for US Letter, and prints on A4 with Fit to page — the same file, no separate download. Because every mark on it is drawn rather than photographed, it stays sharp enlarged to A3, A2 or A1 at a copy shop. Colour carries emphasis only, so a greyscale print of Rational Method loses nothing.Printing guide
Related posters
Charts that sit alongside Rational Method on the same wall.
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