After the annual maintenance period and during the refilling of the canal downstream of a regulator the tail water depth of this canal is small and not sufficient to produce a hydraulic jump inside the solid apron. This results in a severe local scour problem for the canal bed. A traditional solution of this problem is to place crushed rock in the scour hole to prevent further scour; however, this method has not proved to be a permanent solution. To investigate this local scour problem a physical model for a one vent regulator was constructed and a non-uniform granular material was used to simulate the canal bed. This experimental studies revealed that there are five distinct flow regimes in the region of the scour hole, namely: (1) a jet attached to the bed, (2) breaking wave and adverse hydraulic jump, (3) a travelling hydraulic jump, (4) wave jump and diving jet, and (5) surface jet with entrainment from below. The initial tests produced an asymmetrical scour hole; however, a midstream flow divider or vane, made the scour hole more symmetrical. Two depressions were observed inside most of the symmetrical scour holes. It was found that the scour hole that forms immediately after the apron, which is referred to as the short-term scour, reaches an equilibrium depth within a few minutes of the start of flow while the scour hole formed farther from the apron (long-term scour) continues to increase, at a decreasing rate for several days. The short-term scour in a rectangular channel is caused mainly by the attached jet while the short-term scour in a trapezoidal channel is produced by the jet attachment and the drilling effect of the vertical vortices caused by the sudden enlargement at the end of the control structure. The short-term scour in a rectangular channel is found to be a function of the initial Froude number, the initial jet depth and the particle size. The long-term scour depth is caused by the wave jet or diving jet as well as the surface jet; the scour depth was found to be a function of time, densimetric Froude number, initial jet depth and particle size. The changes in the surficial size distribution and settling velocity were determined for short-term and long-term scour at various locations within and downstream of the scour hole. The Gumbel distribution yields a good fit to both fall diameter and mass based equivalent diameter particle frequency distribution. As the scour hole develops, the D$sb{50}$ decreases as does the ratio D$sb{90}$/D$sb{10}.$ An unsteady state short-term scour model was developed to predict the scour hole pattern and duration of phase 1 (attached jet). This model verified the rapid development of the short-term scour depth and reflected the observed effects of head, flow, and grain size. A steady state short-term scour model was developed to predict the scour hole dimensions immediately downstream of the apron. This model confirmed that the short-term scour depth is mainly a function of the initial Froude number, and initial jet depth, although it was found to be weakly dependent on the particle size. A theoretical consideration for the maximum long-term scour depth supports the concept that this depth is dependent on the densimetric Froude number, the jet expansion characteristics and the Shields constant.Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses u26 Major Papers - Basement, West Bldg. / Call Number: Thesis1990 .M653. Source: Dissertation Abstracts International, Volume: 52-11, Section: B, page: 5976. Thesis (Ph.D.)--University of Windsor (Canada), 1990.
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