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

A comparative analysis of a variety of relationships for prediction of basin lag is performed by applying them to 23 basins located in the same geographical area and characterizes by a rather similar vegetative cover. The results of computations indicate that a lag-area relationship 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 non-linear kinematic wave, which at least allows singling 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 hydrological practice.