Erosion of geological units and sediment load in rivers can be considered as the serious problems in recent decades. Increasing sediment loads generate major hazards for water resources development, particularly in terms of loss of reservoir storage due to sedimentation and siltation of water distribution systems. In this paper, the performance of four sediment rating curve (SRC) development methods was evaluated for the Shirin Darreh River (SDR) basin (1750 km2), located in North Khorasan province, Iran. Data of flow discharge (Q) and suspended sediment flux (SSF) (Q-SSF pairs, N=957) and daily flow discharge, recorded by the Regional Water Company of North Khorasan (RWCNK) at the Qaleh-Barbar (QB) gauging site during 1989-2018 were used. The flow discharge classes method performed best by meeting the desired criteria of most statistical indices, including normalized root mean square error (NRMSE), mean bias error (MBE), mean absolute error (MAE), index of agreement (d), and coefficient of determination (R2). Based on the optimized method, the rate of suspended sediment transportation at the study site was estimated about 2.7×106ton year-1. Erodibility of the exposed formations in the study area was estimated based on a factorial scoring model (FSM). Three indices, focused on the outcrop and erodibility, were calculated for the geological units at sub-basin and total scales. Marl deposits are the most extensive geological unit in the three sub-basins and the maximum formation outcrop ratio (FOR) and participation in erosion (PCE) were obtained for these rocks at total scale. In fact, marl unit can be regarded as the main source to supply the suspended sediments in the study basin.

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