evaluation of water chemical quality in sub-basins of gamasiab river

background: in this study, the chemical quality of water in some sub-basins of gamasiab river has been investigated for a long term planning of water consuming in the region . methods: the area is about 11 x10 3 km 2 , located in ramadan and kermanshah, the two western regions of iran. in this regard the results of the water samples, which were collected on the outlet of the 13 hydrometrical stations during 1969 to 1997 (29 years). the major chemical elements such as the cations and anions (ca, na, cl, s04 etc) and the other parameters such as sar (sodium adsorption ratio), tds (total dissolved solids), ec (electrical conductivity) and ph from the rivers (surface water of the basins) were examined. a temporal analysis has been examined using a seasonal classification of the data. the results were analyzed using spss . results: the results illustrate that there are not any significant relationships between the area of the basin and concentrations of the chemical elements. in exception of sar (sodium adsorption ratio) with a 58% variation, in average the others chemical elements show less than 26% variations between the sampling places. the minimum chemical elements have been observed on the outlet of the ali-abad and sahneh, which are the natural basins and also have very small agricultural lands. the values of concentrations of the elements in these two basins are about 50% less than the other basins that are cultivated areas. the highest chemical elements have been observed on the outlet of the pol haj-ali morad. the values of the elements concentration in this basin are about 135% of the average rate of the other basins. the seasonal analysis show that the highest concentration of the chemical elements (in exception of sar) occurs in fall (107%) and the lowest are in spring (94%). in summer, the sar value is maximal . conclusion: the results determine the anthropogenic impacts on river water quality. these may use for water resources management and also modeling of water quality .