Evaluation of Error Due to Applying Average Rating Curve as downstream Boundary Condition in Unsteady Flow Modeling

Journal of Water Science & Engineering

مقاله 1، دوره 2، شماره 4، شهریور 2012، صفحه 7-18   

نوع مقاله: Original Article

نویسندگان

Mehdi Habibzadeh^* ؛ H Mohammad Vali Samani؛ H Kashkuli

Department of Hydraulic Structures, Science and Research Branch, Islamic Azad University, Khouzestan, Iran

چکیده

The rating curve is the relationship between the water stage and the associated discharge in a given
section of a channel. In steady flow, this relationship usually has exponential type, whereas in
unsteady it flow has a looped shape. Since direct developing of actual looped rating curve by using
hydrometric methods is merely possible, steady-state rating curve is commonly used as a downstream
boundary condition in mathematical modeling of unsteady flow which leads to relevant error in model
results. In this study, in order to evaluate this error, a method is presented by using the HEC-RAS
model of unsteady flow in a prismatic channel with different bed slopes, roughness coefficients and
channel lengths as effective parameters. In various channel geometries , the rating curves of both the
approximate and the reference states are obtained. Then statistical comparison between the results was
done. Accordingly, 120 R-squared (R2) values refer to 240 different channel conditions, were
considered and the errors were analyzed which indicate that the error is declined by increasing bed
slope and channel length, in addition by roughness reduction. The maximum rate of the error occurred
by any of effective parameters including bed slope, roughness coefficient and channel length was
evaluated in order of appearance; 0.2617, 0.1507 and 0.1673. In addition, the sensitivity of all the
parameters in different modeling conditions may be distinguished by using the obtained graphs.

کلیدواژه‌ها

Rating Curve؛ Unsteady Flow؛ Mathematical Modeling؛ Downstream Boundary Condition؛ HECRAS

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