ABSTRACT
Relat ively s imple relat ions be tween stage and discharge are presented in Chap te r 4 and normal ly mos t s t reamflow records are based on this principle. By s imply recording stage, therefore, and developing the s t a g e - d i s c h a r g e relation, a con t inuous record of discharge can be obta ined. Several factors, however , can cause scatter o f d ischarge observat ions about the s t a g e - d i s c h a r g e relation at some stat ions. Backwater is o n e of these factors whe reby the velocity is retarded so that a h igher s tage is necessary to mainta in a given discharge than would be necessa ry if the backwate r were no t present . Backwater is caused b y constr ic t ions such as nar row reaches of a s t ream channe l or artificial s tructures downs t r eam such as dams or br idges or downs t ream tributaries. All of these factors can increase or decrease the energy gradient for a given discharge and cause variable backwater condi t ions . If, however , the backwate r caused by a fixed obstruct ion is a lways cons tant at any given s tage, the discharge rating is a function of s tage only. Cons tan t backwater , as caused by sect ion controls for example , will no t adverse ly affect the s imple s t a g e - d i s c h a r g e relation. T h e p resence of variable backwater , on the o ther hand , does not permit the use o f s imple s t a g e - d i s c h a r g e relat ions for the accurate determinat ion of d ischarge.
