Conveyance of one- and two-stage meandering channels

Two-stage channels may be used in flood alleviation schemes to increase conveyance or to provide temporary storage. Their design requires prediction of conveyance, and methods for this have been proposed for straight and meandering main channels with straight floodplains, but not for meandering main channels with sinuous flood-plains. Experimental evidence shows that such channels cannot be considered to be ‘quasi-straight’, and conveyance may be influenced by spill resistance. Conveyance can be estimated as the sum of bankfull discharge and the discharge of the floodplain calculated separately, with the horizontal division plane included in the wetted perimeter for the floodplain. The discharges of the separate simple meandering channels can be estimated by conventional resistance equations, using empirical resistance coefficient adjustments which depend on whether spill resistance occurs or not.