Daily flow duration curve model for ungauged intermittent subbasins of gauged rivers

In this study, we develop a daily flow duration curve model for ungauged intermittent subbasins of gauged rivers. The long-term mean streamflow of the river basin, one of the central parts in the model, is calculated with a regression model of annual precipitation and physical characteristics of the river basin; e.g., drainage area, basin relief, topographical slope, drainage density. The input data of the model are normally accesible, and this makes the model applicable to ungauged points within the river basin. Another central part of the model is the cease-to-flow point which makes the model significant for intermittent rivers. The daily streamflow discharge recorded in gauging stations over the river basin is nondimensionalized by dividing each with their own long-term mean, and their collection is transformed to fit the normal probability distribution; i.e., the normalized nondimensional daily streamflow data are used in the model. The streamflow data are inverted back to the original distribution for any given exceedance percentage by incorporating the cease-to-flow point, and are dimensionalized finally by using the empirically-derived long-term mean streamflow discharge. The model is applied on hundreds of thousands station-day daily streamflow data from three river basins in different geographical regions in Turkey. Results of the case studies are found promising to propose the model as a good foundation for the daily flow duration curve at an ungauged intermittent subbasin of gauged rivers: However, it is noticeable that the model might have low performance in some particular gauging stations where the hydrological behavior deviates from the general characteristics of the river basin. This can be overcome by developing empirical models better approaching the observed long-term mean streamflow, which is a key issue of the model.