A PHYSICALLY-RELATED REGIONAL MODEL FOR EXTREME DISCHARGES IN ISRAEL

Israel is a small country which experiences wide variations in magnitu des of extreme discharges. A consistent model has been constructed for prediction of such discharges throughout the country. Extreme flow ch aracteristics, geographical proximity, lithology, soils, and rainfall properties are the major factors in the delineation of relatively homo geneous regions within the country. For each region, discharge-area re lationships are formulated in association with low exceedance probabil ities. These relationships follow at-site predictions which have been prepared by fitting the log Pearson type III distribution to annual ma xima series of peak discharges. For catchments larger than 100 km(2) i n area, the differences between the regional and the at-site predictio ns are small. Relatively high extreme discharges are found for the ari d area where rainfall depth is low, for an area of steep slopes, for a reas of low permeable lithology and soils, and for areas where the fra ction of intense rainfall in the total depth of precipitation is high. For large arid catchments, the discharge- area relationships exhibit a negative trend. The model is simply applicable and appears suitable for other semiarid and arid areas.