A PRACTICAL (SECTOR BASED) LINEAR WEIR: Fid-Bau Portal

A PRACTICAL (SECTOR BASED) LINEAR WEIR

Murthy, K. Keshava / Swamy, N. V. C. / Rangaraj, C.

This paper presents a linear weir with a comparatively large space below the crest for the collection of grit when used as an outlet weir for rectangular grit chambers. The profile of the weir is geometrically simple to fabricate in the form of a rectangular weir placed over two sectors of a circle separated by a distance. Additional simplicity is achieved in the fabrication, as a result of the elimination of the sharp corner near the crest associated with the earlier designed quadrant plate weir. It is shown that by having a suitable shape of the weir formed with optimum combination of geometrical parameters (width of the rectangular weir, the heights at which the circles are cut at top and the bottom) it is possible to obtain a linear weir (weir having discharge q α h, where h is the head measured above a reference plane), having a very large measurable range of head. For all flows above the threshold depth and within certain ranges of head the discharge-head relationship is valid within ± 1% deviation from the theoretical discharge. The weir when used as an outlet for rectangular grit chambers maintains constant average velocity in the channel. The optimization procedure, ‘Geometric Oscillating Point Method’ is used in this paper. The non-measurable range (‘base flow depth’ or ‘threshold depth’, above which the linearity law is valid) is restricted to be within the sectors. Experiments with two weirs having radii R = 0.10 m and 0.12 m are in excellent agreement with the theory yielding a constant average coefficient of discharge for each weir. The Geometrical simplicity of the profile, accuracy of the weir and a large space for the collection of grit below the crest (a feature which was absent in the Sutro weir) makes it attractive for the practising engineer.