Abstract
In high-velocity free-surface flows, the interactions between the fast-flowing flow and the atmosphere can lead to strong air–water mixing through the free-surface. The flow resistance may be derived from momentum and energy considerations. This was undertaken through some theoretical development based upon an extension of traditional integral approaches to air–water flows, with the re-analyses of detailed air–water measurements in both prototype spillways and large-size physical models. Both the momentum and energy approaches yielded close results in terms of the Darcy-Weisbach friction factor. Based upon the same data sets, the absence of correction coefficients was found to under-estimate the residual energy, compared to the detailed calculations using the relevant air–water kinetic energy and pressure correction coefficients. The finding has basic design implications, which are discussed.