The article presents the research conducted to identify the submergence conditions of the rectangular permeable sill. They were executed as a laboratory tests and analysis aiming at determining the relation describing the submerged flow coefficient (kz). The submerged flow coefficient was calculated on the basis of the submerged to free flow discharge ratio. The analysis include definition of the parameters affecting the values of the submerged flow coefficient and the scientific description of calculation formula. The submerged flow coefficient depends on the ratio of the downstream water depth to the upstream headwater (hd/Hg). The submergence of the permeable sill stream begins when the ratio (hd/Hg) exceeds 0.60. In the initial phase the values of submerged flow coefficient are similar to values given for the permeable sills. The final phase is characterized by submergence flow coefficient similar to values for solid sills.

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