BANKFULL DISCHARGE RECURRENCE INTERVAL IN GRAVEL-BED RIVERS

Bankfull discharge was identified in some 30 gravel-bed rivers represe nting in total c. 40 gauging stations. The catchment sizes vary from 4 km(2) to nearly 2700km(2). Bankfull discharge value increases with bas in size. In the case of gravel-bed rivers developed on an impermeable substratum, the following equation emerges: Q(b)=0.087 A(1.044). Bankf ull discharge recurrence interval was determined by fitting maximum an nual foods (T-a) into Gumbel's distribution and then using the partial duration series (T-p) in this same distribution. Recurrence interval is below 0.7 years (T-p) for small pebble-bed rivers developed on an I mpermeable substratum; it reaches 1.1 to 1.5 years when the catchment size of these rivers exceeds 250km(2). Rivers incised in the soft schi sts of the Famenne show larger channel capacity at bankfull stage, a s mall width/ depth ratio and thus higher recurrence intervals (1.4-5.3 years with T-a and 1-4.4 years with T-p). Baseflow-dominated gravel-be d streams and sandy or silty rivers experience less frequent bankfull discharges, with a recurrence interval higher than 2 or even 3 years ( T-p). (C) 1997 by John Wiley & Sons, Ltd.