Statistical model of daily flow in arid and semi arid regions


1 International Research Center for Living with Desert, University of Tehran

2 M. Sc. Graduate, University of Tehran

3 Faculty of Natural Resources, University of Tehran



Stochastic model for synthetic data generation is not available for daily flows of intermittent streams. Such a model is required in the planning and operation of structures on an intermittent stream for purposes where short time flow fluctuations are important. In this study a model is developed for such a case. The model consists of four steps: determination of the days on which flow occurs, determination of the days on which a flow increment occurs, determination of the magnitude of the flow increment, and calculation of the flow decrement on days when the flow is reduced. The first two steps are modeled by Markov chain. In the third step, flow increments on the rising limb of the hydrograph are assumed to be gamma distributed. In the last step an exponential recession is used with two different coefficients. Parameters of the model are estimated from the observed daily stream flow data for each month of the year. The model is applied to a daily flow series of 20 years’ length. It is seen that the model can preserve the short-term characteristics (The ascension and recession curves and peaks) of the hydrograph in addition to the long-term characteristics (mean, variance, skew ness, and zero flow percentage).