Physical Basis for Quasi-Universal Relationships Describing Bankfull Hydraulic Geometry of Pebble-Bed Rivers

Author

Nicholas A. Haas, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2014

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Wilkerson, Gregory

Abstract

Currently, Manning's equation is widely used to in relating hydraulic geometry to discharge. Here the concept of using bankfull hydraulic geometry to back-calculate the coefficients and exponents of the physical basis underlying hydraulic relationships is used. This method does not make a priori assumptions, and is driven by data; these data represent actual field conditions (within a range of uncertainty). This type of analysis has been performed on gravel-bed and sand-bed rivers. The gap between gravel- and sand-bed rivers (here termed pebble-bed rivers) is examined. Results indicate that: The back-calculated Manning-Strickler relationship has a more complex form than does the standard Manning-Strickler equation, suggesting that the standard Manning-Strickler relationship is not applicable to pebble-bed rivers. Bankfull Shields Stress ( ) and the Reynold's Particle Number (Rp) are inversely proportional; the same is true for gravel-bed and sand-bed rivers. Bankfull sediment yield (Qt,bf) is independent of Rp for pebble- and sand-bed rivers; that is, Qt,bf depends solely on Qbf. This indicates that Qbf is a master variable for predicting Qt,bf. Sediment concentration (C) in pebble-bed rivers should decrease as Qbf increases; C should decrease in the downstream direction. Back calculated and direct regression relationships relating Qbf to hydraulic geometry (Eqs. 45 and 46) are useful relationships for predicting Qbf for ungauged sites along pebble-bed rivers. Eq. (45) has the advantage of being dimensionally homogeneous. Eq. (46) was developed from direct regression and, consequently, is more accurate that Eq. (45) but is not dimensionally homogeneous. This study compliments previous work on gravel-bed and sand-bed rivers. Both studies gave strong evidence to the utility of using a physical-basis and common framework for examining hydraulic geometry. This study adds to those findings.