FLASH-FLOOD FORECASTING-MODEL FOR THE AYALON STREAM, ISRAEL

A composite model for real time forecasting of flash floods in the Aya lon stream in central Israel has been constructed. The model is compos ed of four kinds of sub-models: an autoregressive model for discharges at upstream stations on the two major tributaries; a travel-time mode l for the flow from these stations to the downstream station located o n the main stem of the stream; a time-area concentration curve for sub -watershed drainage between the upstream and downstream stations; and a recession curve for the downstream station. The model incorporates a n adaptive mechanism for continuous correction of forecast errors. Thi s mechanism is calibrated during an initial period of operation, and i s subsequently operated throughout a flow event. The model issues simu ltaneous forecasts for seven lead times ranging from 0.5 to 3.5 h. Thi s provides a proper input for a flood warning system which is required for safe operation of a major highway running along the banks of a to rrent stream in the metropolitan area of Tel-Aviv.