FABRICATION AND CALIBRATION OF SHARP CRESTED WEIRS FOR FLOW MEASUREMENT IN FURROWS

Abstract

This paper reports the fabrication and calibration of sharp crested weirs for flow measurement in furrows. This was done through an experiment on some constructed hydraulic weir models attached to furrows supplied with water through the weirs. The project seeks to determine the coefficient of discharge of the hydraulic weir models and prove the power-law dependence of the discharge and head over the weir models based on the general equation of each of the hydraulic weir models. Three sharp-crested weir models- Triangular, Trapezoidal and Rectangular weirs were constructed and fixed one after the other at one end of the furrows. Waters of known discharges were passed through the weirs, over their crests to the furrow. The corresponding head of water for each discharge was taken and tabulated with the discharge. The coefficient of discharge and slope of the graph of discharge against height for each of the weir models was found graphically and their variations from the standard values were noted and stated. The slopes of the graphs of discharge against height were found to be 2.6, 1.5 and 1.8 as differentiated from the standard values of 2.5, 1.5 and 1.6, and proved the power-law dependence of the discharge and head over the weir models. The coefficients of discharge of the sharp-crested weir models were found graphically to be 3.6134, 1.2632 and 2.563, respectively while their standard values were 0.0702, 0.0953 and 0.0943, respectively. It was deduced that their coefficients of discharge varied from the standard values because of the specifications for the dimensions, which are limits for the length of crest, height of crest, minimum and maximum and maximum heads above crest.