EVALUATING BED-MATERIAL TRANSPORT-EQUATIONS USING FIELD-MEASUREMENTS IN A SANDY GRAVEL-BED STREAM, ARBUCIES RIVER, NE SPAIN

Bed-material load under a wide range of hydraulic conditions was sampl ed in a poorly sorted, sandy, gravel-bed river (Arbucies, NE Spain) du ring 1991 and 1992. The Arbucies data showed a marked scatter of bed-m aterial discharges, reflecting the high variability of bedload rates a s well as of suspended sediment concentrations. Bed-material discharge s were used to test five bedload and bed-material formulae. The degree of agreement between observed and predicted values varies greatly. Th e percentage of observations in which the discrepancy ratio between ob served and computed values has a value between 0.5 and 2, range from 2 5 per cent (van Rijn), to 38 per cent (Brownlie), 52 per cent (Meyer-P eter and Muller), 65 per cent (Engelund and Hansen), and 68 per cent ( Ackers and White). The wide range of hydraulic conditions from which t he data were obtained and the poor sorting of the bed sediment affecte d the performance of the van Rijn (1984) and Brownlie (1981) equations . The degree of correlation between observed transport rates and value s predicted by the Engelund and Hansen (1967) formula appears to be un affected by the poorly sorted bed material of the Arbucies River. The Meyer-Peter and Muller (1984) model predicted bedload transport in the Arbucies River with reasonable accuracy and no bias for transport val ues under low and intermediate flow conditions. The best agreement wit h measured values was obtained using the Ackers and White (1973) model , a reflection of its original design for poorly sorted sediment. (C) 1997 by John Wiley & Sons, Ltd.