Civil & Water Systems
Storm runoff by the rational method with composite coefficients, Hazen-Williams pipe friction with the roughness-constant dataset and fitting equivalent lengths, and traffic-flow fundamentals. Covers §15.0, §16.0, §18.0, §19.0 and §9.48–9.50. Table values are typical published rational-method and Hazen-Williams constants from standard civil engineering practice.
Rational Method: Q = C_f · C · i · A
One surface per line: C area(acres) — the tool area-weights a composite C. Typical C: asphalt 0.85, concrete 0.90, roofs 0.85, gravel 0.50, lawns (sandy, flat) 0.08, lawns (heavy soil, steep) 0.30, woodland 0.15.
Hazen-Williams Friction Loss
h_f = 10.44 · L · Q¹·⁸⁵ / (C¹·⁸⁵ · d⁴·⁸⁶⁵⁵) — L in ft, Q in gpm, d in inches, h_f in ft of head.
Traffic Flow Fundamentals
The rational method's units conspire beautifully: C is dimensionless, i in in/hr and A in acres give Q almost exactly in ft³/s (1 acre·in/hr = 1.008 cfs) — the 0.8% is absorbed into the method's own uncertainty.