عنوان مقاله [English]
Accurate measurement of flow discharge in open channel and water and sewage transmission networks it is of special importance. So far, various types of structures, such as overflows, stomata, flumes and sliding valves, have been proposed for measuring current flow. The proportional weirs are a group of sharp edges weirs that are highly accurate due to low sensitivity to upstream depth variations. In linear proportional weirs, there is a linear relationship between the head and the discharge. In this study, based on theoretical fundamentals of proportional weirs, three proportional linear weirs with linear, triangular and reverse triangular, and two reverse triangles and three series of rectangular weirs were designed and tested in rectangular flume equipped with a side channel in hydraulic lab. About 400 laboratory experiments were carried out lead to, establish a linear relationship between the head and the discharge in linear proportional weirs based on the measurements. The range of the studied discharges varied from 2 to 16 liters per second. The experiments showed that the coefficient of discharge is as a function of two ratios, which are the water depth at the top of the weir and the length of the crest to the height of the weir. Based on these ratios, for each weir a relationship for the discharge coefficient was determined. The average error for proposed equation for linear correlation weirs was equal to 1.5 percent and for over 90 percent of laboratory data the average errors were less than this value. The results show that theoretical sensitivity in linear proportional weirs is equals to one, the more the values of the sensitivity of the studied weir are close to the theoretical values, the better the weir will be. In order to estimate the laboratory sensitivity of the above weirs, the derived relationship between the discharge and head of each weirs was used and compared. The results showed that among linear proportional weirs, inverse triangular weir with a linear relationship, has better and more accurate hydraulic performance.