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HYDROLOGY CALCULATOR — DESCRIPTION & HELP

Seven drainage calculators on one screen. Pick Metric (SI) or Imperial at the top: fields relabel, typed values convert, results come out in the system you picked. Slopes are entered as percent.

1. RATIONAL METHOD — peak runoff Q = C x i x A / 360. C: roof/pavement 0.90, gravel 0.50, grass 0.25. Check: C 0.90, i 50, A 2 = 0.2500 m3/s.
2. SCS CURVE NUMBER — runoff depth + volume. S = 25400/CN - 254, Ia = 0.2S. CN: pavement 98, lawn 74-80, woods 55-70. Check: P 100, CN 80, A 2 ha = 50.5 mm, 1,010.8 m3.
3. KIRPICH — time of concentration from flow length + slope. Check: 300 m, 2% = 7.1 min.
4. MANNING OPEN CHANNEL — rectangular ditch/swale. n: concrete 0.013, grass 0.035. Check: 1 m wide, 0.5 m deep, 1%, n 0.035 = 1.13 m/s, 0.5669 m3/s.
5. MANNING PIPE — full-flow capacity, R = D/4. n: plastic 0.011, concrete 0.013, corrugated 0.024. Check: 600 mm, 1%, n 0.013 = 2.17 m/s, 0.6140 m3/s.
6. RAINFALL VOLUME — 1 mm on 1 ha = 10 m3. Check: 25 mm, 2 ha = 500 m3.
7. REYNOLDS, VARIOUS PIPES — Re = v x D / nu for 14 sizes, 50-1200 mm, each flagged Laminar (under 2,300), Transitional (2,300-4,000) or Turbulent (over 4,000). Viscosity pre-filled, water 20C = 0.000001004. By Velocity: same speed in every pipe. By Flow: same flow, each pipe's own velocity shown. Check: 1 m/s in 100 mm = Re 99,602.

Estimates for planning and checking, not a stamped design. Pipe result is full-flow; entrance losses not included.