Spatial and Seasonal Variation of Suspended Sediment in Different Stations of Gorganroud River, Golestan Province

The amount of sediment load significantly changes along a river due to environmental effects. This variability should be considered to estimate the amount of sediment load. In this research، spatial and seasonal variation of sediment load along of Gorganroud river were evaluated based on the information of 7 hydrometry stations sited in main branch of the river namely، Tamar، Hajighoshn، Gonbad، Voshmgir، Aghghala and Basirabad. Since the amount of sediment load is directly correlated with water discharge، for assuming the effect of water discharge، linear form of sediment rating curve is used where the linear form is produced by the logarithm transformation. Based on this linear relationship with possibly different slopes، the generalized analysis of covariance with logarithm of discharge as its covariate was used to compare the logarithm of sediment load as its response. In order to precisely estimate the amount of sediment load and adequately modify the sediment rating curve، the spatial comparison was drawn separately at low، middle and high rate of water discharge. Spatial evaluation demonstrated an increase in sediment load from Tamer station to Basirabad but there are some distinctive areas between mentioned stations with noticeably decreasing (80% in average) in their sediment load mainly due to reservoir building. For seasonal evaluation of sediment load، the percentage of sediment yield at different seasons was compared. This evaluation revealed that spring with at least 50% and at most 70% of total suspended sediment discharge has the highest amount of suspended sediment yield in this river.