TR-33 : Establishment of rating curve under shifting control

Abstract

Various methods are available to establish the rating curve under shifting control which exists due to various factors such as scour and/or fill, alluvial bed form changes, seasonal changes in vegetative growth etc. This report describes and reviews methods to establish the rating curve under shifting control. When shifting is due to aquatic growth, no mathematical or empirical method is available to establish the rating curve and it has to be established for each season and for all ranges of flooding levels. For shifting due to alluvial bed form changes, Dawdy ‘s analysis is suitable. Three methods namely, constant fall method, normal fall method and the method adopted in SSARR model are available for different situations when shifting is due to backwater variation. Overflow situation is tackled by using Stevens method and slope-conveyance method. Also, it is Quite practicable to establish the ratings separately for the flow in the main channel and in the overflow area. Methods, have been developed by different researchers based on sediment transport theory, to establish the rating curve under scour and/or fill conditions.