Civil engineering Excel templates
Four design spreadsheets you can put straight into a project file, by Michael Flynn, PE. Every formula is visible and unlocked, there are no macros, and each one ships with a worked example already filled in. Each template was checked against an independent calculation before release.
Storm sewer · roadside ditch · detention pond routing · retaining wall · one .zip, instant download
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Storm Sewer Design — Rational method + Manning
Sizes a storm sewer trunk line pipe by pipe, up to 25 runs. It accumulates C×A down the line, carries the time of concentration forward with pipe travel time, reads the intensity from your IDF coefficients, and picks the smallest standard pipe that carries Q flowing full.
- Your agency criteria: minimum Tc, minimum diameter, velocity limits, Manning n
- Override any pipe size; capacity and velocity are re-checked
- Flags over-capacity, low-velocity and high-velocity pipes
Open Channel / Roadside Ditch Design — HEC-15 lining check
Finds the normal depth of a trapezoidal or V ditch, reports velocity, Froude number and critical depth, and checks the lining with FHWA HEC-15 tractive force: bed, side-slope and bend shear against the lining's permissible shear with a safety factor.
- 16 linings built in (erosion-control mats, vegetation classes A–E, gravel, riprap) or your product's tested value
- Depth solved by bisection on a visible sheet, so it always converges
- Flags flow near critical depth (unstable water surface)
Detention Pond Routing — storage-indication (Modified Puls)
Routes your inflow hydrograph (up to 500 time steps) through a pond with a low-flow orifice, a riser weir and an emergency spillway. It builds the stage–storage–discharge rating from your stage–area table, routes it, and plots inflow against outflow.
- Peak outflow, peak water surface, maximum storage, freeboard, spillway activation
- Flags an overtopped stage table and unequal time steps
- Matches an independent fine-step solve to within 0.01%
Cantilever Retaining Wall — stability and stem design
Rankine active pressure with a uniform surcharge, then overturning, sliding and bearing (including the resultant outside the middle third), and ACI 318-19 stem flexure and shear. Every weight, arm and moment is laid out in a table you can check line by line.
- Pass/fail verdict for each check, with what to change when one fails
- Optional passive resistance at the toe; bar size and spacing for the stem
- Same method as the retaining wall calculator, matched value for value
Questions
What do I need to run them?
Microsoft Excel. They were built and tested in Excel for Windows. There are no macros and no add-ins.
Can I change them?
Yes. Nothing is locked or hidden. Change the pipe-size list, the lining table, the criteria, or the formulas themselves.
Can I use them at work?
Yes, on as many projects as you like. The license is per person: please don't resell or redistribute the files.
Do they replace engineering judgment?
No. They are design aids. Check the results against your governing criteria; the engineer of record is responsible for the design. Each workbook's "Read me" sheet states its method, its limits and its references.
Found a problem in a formula?
Email hello@hydrocomplete.com. Fixes go to everyone who bought, through the same download link.
Need PDH? Start with the free 1-PDH ethics course or the 2-PDH storm sewer design course. Studying for the PE? See the PE Civil Water Resources & Environmental practice set.