monitoring of the undesirable phenomenon of thermal stratification in reservoir dam of ekbatan, hamadan

background: dams are one of the most important manmade buildings to provide of drinking water. in order to manage of water quality in dams reservoirs, the recognition of phenomena that occurred in it is essential. thermal stratification is one of the major problems that decrease the water quality of dam. the aim of this study was to investigate thermal stratification of ekbatan dam (hamadan) as the major drinking water supply reservoir. methods: the water sampling locations were determined and the depth-temperature profiles of the dam in various depths were plotted through measurement of temperature and dissolved oxygen (do). thus, temperature and dissolved oxygen at 50 cm intervals up to the depth of 25 meters were determined in the seven stations and monthly samples were taken during one year. the obtained data was compared with wetzel's diagrams. findings: thermal stratification in the dam was started from may until early january (8 months) and it was reached to most severe state in middle of the summer. this phenomenon was disappeared in january and the reservoir remained in mixing state during 4 months in late april. conclusion: with regard to the geographic coordinate and the average elevation (1955 m), the reservoir dam was classified in one warm monomictic with cold circulation during 4 months. therefore, when the dam is in the thermal stratification mode, the water intake depth is a major factor that must be considered.