Author(s): Jacek Czek; Jerzy Ratomski; Slaw Waclawski
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Abstract: The result of investigation on the Tresna water reservoir filling with bedload after 25-year period of its operation are presented in the paper. Two problems were studied: a) changes in the reservoir bowl volume and shape caused by sedimentation and abrasion, and b) the course of sedimentation, distribution of thickness of bedload layers, as well as bedload type and its certain physical characteristics. The investigations showed that the reservoir volume decreased by 4, 8 hm 3 as a result of sedimentation. No changes in the reservoir bowl configuration were found. The old beds of main streams and most of terraces continue to be in the area of sedimentation layers. It was found that the coarse bedload (gravels) was transported and deposited only in the river bedloads es the sedimentation tongues with material selection towards the dam. The fine bedload (sands) was deposited mainly in streambeds, partly on the flooding terraces. Most of the suspended load was deposited in the upper part of the reservoir on the flooding terraces. It consisted of sandy loam, loam and, near the dam, of compact silt loam and silt with organic part mixed as a few per cent. The material is little consolidated. Basing on the analysis of the layout and the type of of the sedimentation layers, it is concluded that the fine bedload (grain fraction ranging from sand to silt and clay) fed into the reservoir by flood flows moves there along old river beds as suspended matter streams.
Year: 1999