Investigation of Temporal Phenomena of Sediment Rating Curve and comparison of it with the Some Statistical Methods for Estimating Suspended Sediment Load (Case study: Gamasiab Watershed)

The variable and complex nature of the sediment load of rivers has led that the estimation of sediment entering the reservoirs and the production of long term sediment, for determining the lifetime of the structures encounter with the problem. Application of sediment rating curves is one of the most common methods for estimating the suspended sediment load of rivers. Regardless of the accuracy of sediment measurement in sampling and measuring the concentration of samples and also measuring the corresponding discharge and with due attention to the spatial and temporal changes of suspended sediment in river management and reform operations, the providing of sediment rating curves is one of the most important resources of error for estimating sediment. Therefore, providing time backup curves for sediment rating curves is necessary for evaluation of accuracy and precision of sediment rating curves. So, in this research are presented time backup curves for sediment rating curves for investigating temporal variations of the sediment rating curve and are applied for considering slope changes of curve and annual changes of it too. Also, in this research compared the results of the sediment rating curve method with the results of some statistical methods for estimating the suspended sediment load in three hydrometric stations in Gamasiab watershed. The results of validations showed that transfer function model due to take into account time parameter with SSE 0.00003 ton/day, 3.24 ton/day, 5.92 ton/day, respectively for stations: Sang-Surakh, Vasaj and Marvil has high precision in the forecasting and moreover it presents confidently unbiased forecasts for the future.