Operation optimization of the reservoirs has been mostly carried out based on general objectives, including

water demand supplies, power generation, flood management, and environmental constraints. In most

of the previously developed models, sediment removal from reservoirs has not been included. Flushing is

one of the most important and common ways of retrieving the lost volume of reservoirs due to sedimentation.

Despite its adverse effects on the environment of downstream rivers, this method has received lots of

attention by engineers and researchers in the past. One of the main drawbacks of the previous studies in

the field of reservoir operation optimization has been lack of modeling tools for considering the relation

between sediment removal and other objectives of reservoir operation. In this paper, a new approach has

been developed for monthly reservoir operation optimization. For this purpose, a model has been formulated

to minimize the total deficit in supplying demands and to maximize the total volume of sediment

removed from the reservoir. The objective function for sediment outflow has been developed using the

flushing method. The optimization model has been formulated using Varying chromosome Length Genetic

Algorithm (VLGA). The efficiency of the model has been tested in the case study of Sefidrud Reservoir in

North of Iran. The results of the optimization model for a 5-year period have been compared with the historical

records of the operation of the reservoir. The results of the case study have been summarized in the

form of practical operating rules for flushing and operation management