Approximating wetted perimeter in power-law cross section

The wetted perimeter is an open-channel. parameter that influences surface drag and also influences infiltration in furrows and unlined canals. Variou s approximations to the wetted perimeter are examined for channel cross sec tions in which the top width is a power law of depth. Exact solutions are a vailable only for select values of the exponent. Interpolation between exac t values, partial sums of series approximations, and numerical integration are compared. A simple nonlinear interpolation scheme or a three-term summa tion yields results accurate to within 1% of the range of typical channel g eometries. Common numerical approximations are shown to yield errors in exc ess of a range of from 3 to 10%.