Hydraulic modelling of a sharp crested labyrinth weir

Sitompul, Adolf Tommy (1993) Hydraulic modelling of a sharp crested labyrinth weir. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (24MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

A labyrinth weir is an attractive alternative for water level control in flat land where the head is usually limited. It is also useful in a river where the weir width is confined by the topography. The advantages occur because the crest length of a labyrinth weir is significantly longer than the width of the river. This is achieved by having a plan form which consist of repeating geometric cycles, typically trapezoidal in form. As a result large flows can be released at relatively low heads. Trapezoidal and triangular forms have become the favoured geometric cycles for designers. -- This study on a labyrinth weir was undertaken to confirm the operating parameters as well as to investigate different plan shapes including rectangular, rectangular with a semi-circular connection and reverse trapezoidal. Experimental and theoretical results confirmed that the trapezoidal shape with the side wall angle, α = 0.68 αmax, and the length magnification, 1/w = 2.65 gave the best hydraulic performance among other labyrinth weir plan forms which were tested in this study. The effect of varying the crest width was also investigated in this study. This part of the study focused on the trapezoidal shape. It was shown that increasing the width of the crest up to 10 mm (in this case 10% of weir height, P) was not significant in decreasing the flow despite some frictional losses on the crest. Such a crest is useful when a river has a large quantity of debris. -- The economic advantages of labyrinth weirs were also studied with reference to the Ciwadas trapezoidal labyrinth weir which was constructed in Indonesia in 1988. This labyrinth weir was designed to handle the flood flows of 200 m³/s and control water depths between 1.6 m and 2.35 m. Comparison with a typical weir with gate shows that this labyrinth weir was more than 25% less expensive. -- A computer code for analytical studies was also established. It was shown that for trapezoidal plan forms, a good agreement between theoretical results and experimental data could be achieved. This also confirms the previous theoretical solution proposed by Hay and Taylor although there is a little difference (0.1) in defining the value of the energy loss coefficient (contraction) at the entry to the weir.

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