عنوان مقاله [English]
In this paper, using the 39 years of water surface fluctuation data and surface inflows, precipitation on the lake, evaporation from the free surface and iso-potential groundwater maps, the main parameters for water balance in the lake are calculated. Then these parameters are compared for long-term, wet and dry periods. According to received results, the maximum and minimum values of the water surface level of the lake is 1278.41 and 1273.23 meter above sea level, respectively. These extremes are observed in water years of 1373-74 and 1380-81 correspondingly. The Maximum and minimum variations in volume has occurred in 1347-48 and 1377-78, that they are introduced as a wet and dry years, respectively. The suitable elevation for lake is between 1275 to 1246 meters above sea level. The mean elevation based on 39 years of recorded data is 1275.6 m above sea level. In order to increase the level from 1273.23 to 1275.6 meter, about 7.4 billion m3 of water should be reserved. For this condition to occur, a wet year (i.e. 1347-48) or a long-term average for five successive years should happen. Also the variation rate for inflows are about %343 grater than outflows factors. Finally, after the considerating of the lake balance, management actions are presented for better exploitation of water resources and environmental preservation of Orumieh lake basin.