SGER: Stage-Discharge Relationship (Rating Curve) and Associated Uncertainties

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

0098835 Yen The flow rating curve showing the relationship between water-surface stage and the flow discharge has been widely used in hydrology for over a century. Direct measurements of discharge in open channels is costly, time consuming, and impractical during floods. Difficulties with stage-discharge ratings have long been recognized. The relation between stage and discharge is not unique. The water slope and changing channel cross sections result in a range of possible discharges for the same stage. A number of methods have been proposed to improve the fit but have not adequately assessed the fundamentals of stage-discharge ratings based on fluid mechanics. This work would explore the feasibility of deriving the rating for a stream reach theoretically. An important feature in the project design is the close collaboration with the Illinois USGS office that tie the theoretical to work years of practical experience. The approach would develop rating curves without stage or discharge measurements by using the unsteady-flow equation. The recently developed Hydraulic Performance Graph (HPG) contains all the information needed to develop a relation between the stage, the water-surface slope, and the discharge. Unsteady-flow equations will also be explored. The result sought is a rating curve supplemented with graphs or equations representing the correction due to additional contributing factors, such as water-surface slope, in a nondimensional form. Measured data will be used to verify the rating curve, instead of deriving it, allowing considerable savings in time, cost, and effort in data collection. Furthermore, the work includes a preliminary investigation of the uncertainties associated with the individual contributing factors and the overall uncertainty of discharge determination from stage.