Investigation of the Relationship between Sediment Graph and Hydrograph of Flood Events (Case Study: Gharachay River Tributaries, Arak, Iran)

Abstract

In the comprehensive management of watersheds, the knowledge of the sedimentation process in flood conditions is considered as an important and challenging issue. The aim of this study was to investigate the hysteretic behavior of suspended sediment concentration (C) in relation to the discharge. To achieve this goal in Gharachay river tributaries, eleven flood events recorded in 2004–2005 and 2006–2007 were selected. Suspended sediment sampling carried out by using the USDH-48 sampler in three cross-sections. By determination of C in laboratory and separation of base flow of flood hydrograph, sediment graph of each flood produced and main parameters of each hydrograph and sediment graph were investigated. In addition, concurrent concentration-discharge graph (C–Q) of each flood events was depicted and the shape of each C–Q loops related to C during rising and recession limb of the hydrograph. The results showed that coefficient of variations (Cv) of C in selected events varied from 12.58 to 119.87%, while the minimum and maximum C of the mentioned floods were 191 to 387 and 800 to 4800 mg/L, respectively. The maximum amount of C was about 15 700 mg/L which belongs to the flood events with Cv of 76%. Comparison with the sediment graph the Cv of floods hydrograph was low (5.4 to 59.2%). Investigation of correlation matrix between flood hydrograph and sediment graph parameters shows that there were no meaningful relationships between selected parameters. However, C–Q relations during single flood event and form of its loop show that in most cases the rising limb of hydrograph has the high amount of sediment concentration, which reflects the closeness of sediment sources to the basin outlet.