Assessment of Base Flow Separation Methods at Karaj Dam Watershed

Assessing existing water resources along with different routes of the river in a watershed is essential for its optimum use, conservation, and predicting flood and minimum flow. In addition, identification of runoff production processes is also important for assessing the effects of climate change and landuse on the hydrologic response of the watershed. There are several methods for separating base flow. In this study, the minimum local methods, sliding intervals, fixed intervals, one -parameter recursive digital filter and two -parameters recursive digital filter method were used for separating base flow at four hydrometric stations of Karaj River basin with a statistical period of 22 years (1991-2012). Then, the results were compared to determine the most appropriate method. The results showed that at Sierra-Kalvan and Nashtarod stations, the one-parameter recurrsive filter method with alpha of 0.925 and 0.950 could be a suitable method for estimating the base flow, due to the lack of significant differences between their results, as well as the minimum standard deviation. For Mored and Sierra stations, the one -parameter recursive digital filter with alpha values ​​of 0.950 and 0.975 was considered as a suitable method in separating base flow because of the lack of significant differences between their results as well as the standard deviation. The one -parameter recursive digital filter, therefore, has high spped in separating the flow hydrograph and can determine the continuous values of base flow.