Estimation of the suspended sediment load in rivers with different hydrological methods (case study: Siahrood river in Mazandaran)

In a watershed, sediment arises due to the erosion and some factors such as pastures destruction,change users, no reasonable cultivation. That causes problems such as sedimentation in reservoirs andreduces their useful volume, reducing water quality in agricultural consumption; reduce the efficiencyof hydraulic structures and some other environmental problems. Changes in sediment load in a riverare an important parameter in water management projects and are an indicator to show the status ofsoil erosion and ecological conditions of the area. The estimations of the sediment load are used in awide range of issues such as designing reservoirs, sediment transport in rivers, determining the effectsof watershed management and environmental protection. This study is denoted to Siahrood river inMazandaran province which is the main source of the water supply for a large part of the farm fieldsarea. In this project, by studying the efficiency of sediment rating curves and selecting the mostappropriate curve, the amount of suspended sediment load of the river is estimated perfectly. For thispurpose, the daily discharge of flow and corresponding statistics flow discharge–suspended sedimentdischarge, which are measured simultaneously in some days of year, during a statistical period of 13years (from 1998-99 to 2010-11), from the only hydrometric station in the main route of the river, isused. For the selection of appropriate curve, we use statistical indicators mean squares of error andcoefficient of determination was performed then, by drawing rating curves of linear, multilinear andmediocrity categories for this river, the rating curve of mediocrity categories with coefficient ofdetermination 93% was chosen as the appropriate sediment rating curve. Eventually, the amount ofsuspended loads is estimated by use from various methods discharge of flow. These methods containthe rating curve of mediocrity categories combined with the average daily water flow, averagemonthly water flow, flow duration curve and combination of monthly and daily average dischargemethod. Finally, the results of each four methods is compared together, and rating curve of mediocritycategories method and combining it with average daily water flow is selected as the most appropriatemethod. Moreover, the amount of suspended sediment load at hydrometric station is estimated about55855 tons per year by selected method.