Issues
Issue 003 · April 27, 2026
Why your Manning's n estimate is probably wrong (and why it matters more than you think)
A worked example showing why a 15% swing in Manning's roughness coefficient produces a 20% swing in design discharge — and a practical way to bound the real uncertainty before you sign and seal.
Issue 002 · April 24, 2026
Kirpich vs NRCS: when time of concentration disagrees by a factor of two
The two most-used Tc formulas can disagree by 2× on the same watershed. Kirpich was calibrated on rural Tennessee in 1940; NRCS lag is calibrated for modern urban/suburban work. Pick the wrong one and your peak flow is off by 30%.
Issue 001 · April 20, 2026
The runoff coefficient C is the dirtiest number in stormwater
Q = C·I·A is the simplest peak-runoff equation in civil engineering. The C is also the dirtiest number — varying by 4× for the same land cover depending on whose table you read. Why the disagreement exists, and what to actually use.
Issue 004 — May 2026 · Topic in progress. Subscribe above to get it the day it ships.