Determination of optimized sediment rating equation and its relationship with physical characteristics of watershed in semiarid regions: A case study of Pol-Doab watershed, Iran

Document Type : Research Paper


1 Faculty of Natural Resources, Yazd University, Yazd, Iran

2 Yazd Regional Water Authority, Yazd, Iran


Managers always consider the precise estimation of sediments in watersheds due to various conditions, such as
soil and water resources management, construction, infrastructure and economical and social issues. In this condition,
an optimized determination of sediment rating equation (typical method until now for sediment yield estimation) is
essential to investigate sediment yield in rivers. In this study, the best sediment rating equation was determined for
four hydrometric stations of Pol-Doab watershed in Markazi province using sediment rating curves types (singlelinear,
multi-linear, mean loads) together with bias correction factors (FAO, Quasi-Maximum Likelihood Estimator
[QMLE], Smearing, Minimum Variance Unbiased Estimator [MVUE] and β). The results showed that the optimized
equation in stations is the mean loads (MVUE), which can used for prediction of sediment yield in annual scale.
Moreover, FAO factor is more accurate for the estimation of sediment yield in high variability conditions for
monthly, weekly and daily scales. According to the obtained results, accurate representation of variability intensity of
sediment yield is associated with the rating curves types, since the monthly rating curve is more accurate. Also, the
results indicated that the watershed average slope has direct relation with b coefficient of rating equation, and when
using this parameter, the rate of sediment yield can be determined for month, season and hydrological periods. Based
on the obtained results, with increase in the watershed average slope, the slope of suspended sediment concentration
(SSC) equation is also increased.


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