This tool computes uniform flow in partially full pipes and open channels using Manning's equation, with the standard section geometry relations from FHWA HDS-4 and HDS-5 (public domain US DOT publications). Five section types are supported: circular pipe, rectangular tube, rectangular channel, flat bottom (trapezoidal) channel, and vee channel. Four modes are available: solve for the flow rate at a given depth, solve for the normal depth at a target flow rate, compute volumes and weights, and estimate thermal length expansion.
Beyond the basic solution, the calculator reports the critical depth for the computed discharge, partial-flow ratios (Q/Qfull, V/Vfull) for closed conduits, and design velocity checks (self-cleansing minimum and permissible velocities for erodible channels per Fortier and Scobey, as tabulated in Chow, 1959), and plots the full discharge curve Q(y) with the current case, critical depth, and the depth of maximum discharge marked. The built-in reference database covers 12 pipe series, 37 Manning roughness values, 18 materials, and 56 fluids. Multiple cases can be collected into a data table, each with its own 3D schematic, and exported as a single PDF calculation sheet.