Manning's Equation Calculator

Manning's equation, V = (k/n) R^(2/3) S^(1/2), worked for open channel flow in metric or US customary units. Pick a rectangular, trapezoidal, triangular or part-full circular section and the first tab returns the flow area, wetted perimeter, hydraulic radius, velocity, discharge, Froude number and critical depth. The second solves for normal depth by bisection, since the depth sits inside both the area and the perimeter and cannot be rearranged out. The third gives the bed slope a given discharge and depth would need. Roughness comes from a list of named linings that you can override with your own n.