Bar resistance in gravel bed streams at bankfull stage


  • Karen L. Prestegaard


Total flow resistance in gravel bed streams with high width/depth ratios and low sinuosities is primarily a result of grain and bar roughnesses. The relative importance of these two roughness elements has not been established. The relative importance of grain and bar resistance is examined for 12 straight and divided gravel bed reaches at bankfull stage by using the Keulegan equation to determine a resistance division of energy slope. The remaining slope is assumed to represent the relative importance of bar resistance. Bar resistance accounts for 50 to 75% of the total resistance in these reaches. Calculated values of reach-averaged bar slope correlate closely with field measurements of bar magnitude.