Trapezoidal (Cipoletti) Weir Calculator

Computes discharge over a trapezoidal (Cipoletti) weir as a simplified estimating relation. The standard Cipoletti case (z = 0.25, i.e. 1H:4V side walls) uses the rectangular crest term only because the triangular flare is absorbed into the Cipoletti coefficient. Other side slopes add a triangular correction term. Verify against project-specific coefficients before final design.