Statistical modelling of daily streamflows using rainfall input and curve number technique

For modelling the uncertainties associated with the random field of rainfall and runoff a simple statistical daily streamflow generator with simulated rainfall input is presented. This can also be used in situations where long series of daily rainfall are available to extend short flow records. Wet and dry runs of rainfall are generated using the geometric and log-series distributions, respectively. Rainfall input is simulated based on a gamma distributed daily rainfall but with exponentially decreasing means and standard deviations within each rainfall event. Losses are obtained from an equivalent curve number, CN, related to the total rainfall of the event. The CN is treated as a random variable in the simulation of streamflows. Ordinates of the unit hydrograph used in converting excess rainfall to runoff are also considered to be variables.