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Physical Modeling for Side-Channel Weirs

by K.-L. Lee and E. R. Holley

ABSTRACT

In a previous project, experiments were conducted to determine the hydraulic characteristics of embankment-shaped side weirs in trapezoidal channels with 2.5H:1V side slopes. The present project built on the work done in the previous project. Data from the previous project was reanalyzed, and computations of water surface profiles along side weirs were used to evaluate the effects of channel slope and roughness on weir hydraulics. It was concluded that both the slope and roughness of the main channel should be included explicitly in the calculations of side-weir flows.
The physical model was modified to have 4H:1V side slopes, and additional experiments were conducted on side-weir flows. These experiments included both the characteristics of the weir flows and the size and hydraulic effects of the separation zone created in the main channel by the side-weir diversion flow. Based on the experimental results, it is recommended that side-weir discharges be calculated using integration along the weir length and empirical coefficients for the discharge per unit of weir length rather than bulk coefficients for the entire discharge. Empirical formulas are presented for embankment-shaped side weirs.
Limited experiments were conducted to evaluate the effects of channel flow on the hydraulics of culverts used for diversion.
The empirical results presented in this report were incorporated into a computational scheme for side diversions. That computational scheme is presented in a companion report ("Side-Diversion Analysis System", CRWR Online Report 02-3).

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