FREQUENCY AND MAGNITUDE OF RUNOFF EVENTS IN THE ARID NEGEV OF ISRAEL

An event-based regional model for the frequency and magnitude of runof f events in the arid Negev of Israel has been developed. The model con siders the number of events in a year, their arrival times, maximum ob served discharges and volumes, the distribution of peak discharges and event volumes, and regional relationships between catchment area and magnitudes associated with 10- to 100-year recurrence intervals. The o ccurrence of events follows a negative binomial distribution with para meters estimated from the mean and the variance of the number of event s in a year, which, in turn, are positively correlated with the mean a nnual depth of precipitation over the catchment. Arrival times of even ts follow the Pearson type-3 distribution. The enveloping curve of the maximum observed volumes is related to the catchment area by a power function. For catchments smaller than 250 to 300 km(2) in area, the di scharges and volumes associated with 10- to 100-year recurrence interv als are found to be proportional to the catchment area. For large catc hments, the discharge-area relationship may yield an inverse trend, an d the volume may cease to increase as the area increases. Locations of the turning points for the relationships vary between watersheds. (C) 1998 Published by Elsevier Science B.V. All rights reserved.