Open channels are one of the most used water conveyance systems to deliver water for diﬀerent purposes. Existing models for the design of open channels mainly assume uniform ﬂow, focus on cross-section sizing, and generally decouple cross-section sizing from the selection of channel alignment and proﬁle. This study developed an optimization model for a comprehensive design of conveyance channels. The model minimizes the sum of costs for earthwork, lining, water losses, and land acquisition; accounts for non-uniform, mixed-regime ﬂow; and considers multiple geometric and hydraulic constraints. The model was validated using several idealized scenarios. The model potential in minimizing the cost of real open channel projects was demonstrated through application to an existing irrigation water transmission canal in Egypt (the Sheikh Zayed Canal). The results of validation scenarios matched the anticipated outcomes for channel proﬁle and alignment and reproduced analytical solutions given in the literature for channel cross-section design. Application of the model to the Sheikh Zayed Canal gave a more optimal design; the OCCD model produced a design alternative with ~27% less cost than the constructed alternative.