Free, instant, no signup. The checks we run dozens of times a week — built properly, documented, and open to every engineer.
Draw a site and auto-derive a TR-55 Curve Number from satellite land cover and SoilGrids soil, plus screening hydrology (Rational, SCS-CN, Tc), DEM terrain analysis, a delineated catchment, a flood-risk band and the studies you'll need — every assumption declared.
Run site screening → Q = (1/n)·A·R2/3·S1/2Full and partial circular pipe capacity, plus trapezoidal open-channel flow with Froude number. Velocity, discharge and flow regime — instantly.
Open calculator → Q = C·i·A / 360Peak discharge for small catchments with composite runoff coefficient support and a built-in C reference table for common surfaces.
Open calculator → Tc = 0.0195·L0.77·S−0.385Two methods computed side by side from one set of inputs, with guidance on when each is appropriate. Feeds straight into the Rational Method.
Open calculator → ys = 2.0·K₁K₂K₃·a0.65·y₁0.35·Fr0.43Local scour at a pier with live scour-hole section — nose shape, skew and bed-condition factors, plus the HEC-18 upper-limit check most calculators skip.
Open calculator → Q = 1.66·P·d1.5 | 0.67·A·√(2gd)Grate and curb-opening inlets in sag — weir and orifice regimes computed together, clogging factor applied, live gutter section showing the ponding.
Open calculator →These tools handle the quick checks. For calibrated 2D models, network design and Stage 4 IFC — that's our day job.