Lag prediction in ungauged basins: an investigation through actual data of the Upper Tiber River valley

A comparative analysis of a variety of relations for prediction of basin lag is performed by applying them to 23 basins located in the same geographic area and characterized by a rather similar vegetative cover. The results of computations indicate that a lag-area relation with two constant parameters is the best predictor for most basins; under different vegetative covers in the same basin only one parameter should be variable. For a few other basins characterized by an anomalous drainage channel network of low density, such a relationship can lead to unacceptable errors. Thus, there is a need for an additional relationship to overcome this difficulty, but a larger number of anomalous basins would be required for its determination. An alternative procedure, based on the use of the nonlinear kinematic wave, which at least allows to single out the cases where a specific lag-area relationship is not reliable, is proposed. This procedure, therefore, represents a partial but very useful solution to avoid considerable errors in hydrologic practice.