The free overfall as a flow measuring device in a circular channel

The critical depth of flow (h_c) and the brink depth (h_b), for a circular pipe with and without a horizontal bed are used to estimate the channel discharge. The brink depth ratio (h_b/h_c) for a given cross section geometry is shown to be a constant for subcritical flow. The brink depth ratios for various channel geometries and bed slopes are presented in a form readily accessible to engineers. Two worked examples, one for an irrigation channel and the other for a larger circular sewer, show how the discharge Q can be obtained from measurement of the brink depth.