Abstract:
THE IOWA INSTITUTE OF HYDRAULIC RESEARCH IS ENGAGED IN A LABORATORY INVESTIGATION OF FOUR PHASES OF SCOUR AT BRIDGES: (1) GEOMETRY OF PIERS AND ABUTMENTS, (2) HYDRAULIC CHARACTERISTICS, (3) SEDIMENT CHARACTERISTICS, AND (4) GEOMETRY OF CHANNEL CROSS-SECTION AND ALIGNMENT. STUDY OF PHASE 2 INDICATES EQUILIBRIUM DEPTH OF SCOUR IS PRIMARILY DEPENDENT ON THE DEPTH OF FLOW AND THAT VELOCITY HAS LITTLE INFLUENCE ON EQUILIBRIUM CONDITIONS. THE INSTANTANEOUS RATE OF SCOUR, HOWEVER, IS GREATLY INFLUENCED BY THE VELOCITY, AND SCOUR DEPTHS IN EXCESS OF THE EQUILIBRIUM CONDITION CAN BE ATTAINED UNDER UNSTEADY FLOW CONDITIONS. A FLOOD, OF COURSE, IS A STATE OF UNSTEADY FLOW, AND AN ALLUVIAL STREAM WILL HAVE A TENDENCY TO DEGRADE DURING THE RISING STAGE. THE LOWERING OF THE BED RESULTS IN A VARIABLE LEVEL TO WHICH THE SCOUR DEPTH, AS DETERMINED BY THESE LABORATORY TESTS, MUST BE REFERRED. FURTHER INVESTIGATION IS NECESSARY HOWEVER, TO DETERMINE WHETHER THE EXCESS DEPTH OR THE EQUILIBRIUM DEPTH OF SCOUR WILL OBTAIN DURING THE SLOWLY VARIED FLOW OF FLOODS. /AUTHOR/
Supplemental Notes:
Vol 31, pp 82-87, 4 FIG, 2 TAB, 1 PHOT. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
