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Improving the hydraulic performance of single step broad-crested weirs

Authors: Saleh J. S. Shareef --- Inam A. K. Juma --- Hamid H. Hussein
Journal: Iraqi Journal of Civil Engineering المجلة العراقية للهندسة المدنية ISSN: 19927428 Year: 2011 Volume: 7 Issue: 1 Pages: 1-12
Publisher: University of Anbar جامعة الانبار

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Abstract

Abstract

In this study the hydraulic performance of single step broad-crested weir was improved. Through analyzing the parameters that have effect on the shape of the step and its influence on the flow characteristics, and energy dissipation percent (E%) downstream (D/S) of the weir. The differential equation of gradually varied flow for the water surface profile over the weir was solved analytically .Furthermore, empirical relations for E% and discharge coefficient (Cd) due to the affecting factors were derived .The results showed that the weir model when the ratio of the length of D/S step to the length of the weir L2/L1=0.5 gives a higher E% in comparison with other weir models. Three types of flow regimes were observed, nappe flow below 350 cm3 /s/cm, transition flow 350-700 cm3/s/cm and skimming flow upper than 700 cm3/s/cm . The comparison between calculated values by the differential equation of gradually varied flow and experimental values gives a good agreement, the maximum difference is about 7%.Two empirical relations were obtained, the first to estimate Cd in terms of the ratio for upstream U/S water head to U/S weir height H/P1 and L2/L1. While the second relation to estimate E% in terms of the ratio for D/S water head to U/S weir height h/P1, L2/L1 and the Froude number Fr2 with a high correlation coefficient .
Key words: Hydraulics; weirs ; performance ; dissipation energy.

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