Diaphragm Height of Ejector of Uniform Sediment

Abstract

Sediment entry into irrigation and hydropower canals may be controlled by a sediment excluder at canal headworks and/or a sediment ejector on the canal downstream of headworks. These devices take advantage of the fact that the bed‐load part of transported sediment in a stream moves near the bed and the suspended‐load part is distributed nonuniformly in a vertical column, with heavier concentrations near bed. The sediment ejector consists of a horizontal diaphragm slab, positioned slightly above the canal bed, and of ducts below the diaphragm flush the heavy sediment‐laden water into an escape channel. The present study concerns determination of diaphragm height of the ejector for uniform sediment, based on principles of sediment transportation. The diaphragm height should be such that suspended sediment load in the canal approaching the ejector above the diaphragm level should be equal to the total sediment transport capacity of the canal downstream of it. A correction factor is suggested to account for the effect of flow disturbance at the nose of the ejector. A design example has been worked out.