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Critical flow in control sections prevents the downstream water level and flow conditions from affecting the flow through the critical sections, and the discharge can be computed as a function of the measured upstream head. Measurements of irrigation water flows in field channels have usually been expensive, too often of questionable accuracy and otherwise difficult to apply to all field situations. The techniques available in open channel hygrometry are the use of hydraulic structures (devices), velocity-area methods, dilution techniques and slope-hydraulic radius and area methods. Considering the constraints in the measurements of low discharges in open channels, hydraulic structure technique is best suited. Crest height had been increased from 10 cm to 25 cm then the C_d values also decreased from 0.82 to 0.50 for discharge decreased from 24 to 6 Ls^-1 under free flow conditions. The co-efficient of discharge for the different weirs under 60 per cent submergence conditions, if the increased crest height was from 10 cm to 25 cm then the C_d values also decreased from 0.75 to 0.43 for 24 to 6 Ls^-1 discharge. Under 75 per cent submergence conditions, if the increased crest height was from 10 cm to 25 cm then the C_d values also decreased from 0.7 to 0.42 for discharge decreased from 24 to 6 Ls^-1. Under 90 per cent submergence conditions, if the increased crest height was from 10 cm to 25 cm then the C_d values also decreased from 0.69 to 0.42 for 24 to 6 Ls^-1 discharge. For 24 Ls^-1 discharge, the co-efficient of discharge has been decreased from 0.72 to 0.62 for increased submergence levels from 60 per cent to 90 per cent due to increase in contact surface area and friction and less discharge have low velocity of approach.

Keywords

Flume, Weirs, Co-efficient of Discharge, Crest Height, Discharges.

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References

Al-Hamid, A.A., Negm, A.M. and Al-Brahim, A.M. (1997). Discharge equation for proposed self- cleaning device. J. King Saud Univ. Eng. Sci., 9 (1): 13 – 24 .

Baddour, R.E. (2008). Head-discharge equation for sharp-crested polynomial weir. J. Irrigation & Drainage Engg., ASCE., 134(2) : 260-262.

Castro-Orgaz, O., Giraldez, J.V. and Ayuso, J.L. (2008). Critical flow over circular crested weirs. J. Hydraulic Engineering, ASCE, 134(11) : 1661-1664.

Chow, V.T. (1959). Open channel hydraulics. Mc Graw-Hill Book Company Ltd., NEW YORK, U.S.A.

El-Saiad, A.A., Negm, A.M. and Waheed El-Din, U. (1995). Simultaneous flow over weirs and below gates, Civil Engineering Research Magazine, Civil Engineering Department, Faculty of Engineering. Al-Azhar University, Cairo, Egypt, 17 (7): 62-71.

Gogus, M., Define, Z. and Ozakandemir, V. (2006). Broad crested weirs with rectangular compound cross sections. J. Irrigation & Drainage Engg., ASCE, 132(1) : 272-280.

Hayawi, H. A. M., Hayawi, G. A. M. and Alniami, A. A. G. (2009). Co-efficient of discharge for a combined hydraulic measuring device. Al Rafidain Engg. , 17 (6) : 92-100 .

Ismail, M.H. (2012). Experimental investigation for flow through combined structure weir and gate. Thesis, College of Engineering, Kufa Universit.

Mahboubeh, S., Nasser, T., Dehghani, A. A., Abdoul Rasoul, T. and Reza, R.G. (2011). Experimental investigation of the effect of contraction on scouring in downstream of combined flow over weirs and below gates. 5thSASTech, Khavaran Higher - education Institute, Mashhad, IRAN.

Negm, A.M. (2002). Discussion of analysis and formulation of flow through combined V - Notch - Gate - device by A. A. Al- Hamid. J. Hydraulic Res.,40 ( 6): 755 - 765. Negm, A. M., Al-Brahim, A.M. and Al-Hamid, A.A. (2002). Combined free flow over weirs and below gates. J. Hydraulic Res., 40 (3): 359 - 365.

Ramamurthy, S.A., Junying, Q.U., Zhai, Ch and Diep, V. (2007). Multislit weir characteristics. J. Irrigation & Drainage Engg., ASCE, 133(2) : 198-200.

Raouf, E. and Baddour, M. (2008). Head-discharge equation for sharp-crested polynomial weirs. J. Irrigation & Drainage Engg., ASCE, 134(2) : 260-262.

Samani, Z., Jorat, S. and Yousaf, M. (1991). Hydraulic characteristics of circular flume. J. Irrigation & Drainage, ASCE, 117(4) : 558-566.

Satyanarayana, T.V. and Satyanarayana, T. (1994). Effect of weir geometry on co-efficient of discharge of modified trapezoidal broad crested weirs. J. Institution of Engineers (India), Agric. Engg. Division, 74(1) : 38-42.

Effect of Crest Height on Flow Characteristics of Semi-Circular Bottom Contraction Weirs

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Authors

D. Sai Gangadhara Rao ¹, T. V. Satyanarayana ², H. V. Hema Kumar ², K. V. S. Rami Reddy ²

Affiliations
1 College of Agricultural Engineering Bapatla (A.P.), IN
2 College of Agricultural Engineering, Bapatla (A.P.), IN

Source

International Journal of Agricultural Engineering, Vol 8, No 1 (2015), Pagination: 21-25

Abstract

Accurate water measurements systems enable accurate accounting of water use, and permit the available water to be supplied at optimum rates to the areas where it is intended to be used. A perfect understanding of some of the primary principles relating to the subject of water measurement is, therefore, necessary for establishing any water measurement system in the canal commands of irrigated agriculture. All the four weir types have enabled creation of critical flow conditions within the throat section, which indicate their suitability for measurement of water in open channels in general. All the four design crest heights (25 cm (Weir-I), 20 cm (Weir-II), 15 cm (Weir -III) and 10 cm (Weir-IV)) are found to be acceptable excepting for 90 per cent submergence level condition. Critical depth (section) has occurred at only one location in the throat section for all the weirs under all possible conditions. The crest height has increased from 10 cm to 25 cm and then location of the critical section has moved towards the upstream side from 1.6 to 0.8 cm, 1.7 to 1.0 cm, 1.8 to 1.1 cm for 24 Ls^-1 discharge under free flow, 60 per cent, 75 per cent submergence conditions, respectively. For 18 Ls^-1 discharge, crest height has increased from 10 cm to 25 cm, and then location of the critical section has moved towards the upstream side from 7.0 to 3.1cm, 7.1 to 3.3 cm, 7.3 to 3.5 cm under free flow 60 per cent, 75 per cent submergence conditions, respectively. For 12 Ls^-1 discharge, crest height has increased from 10 cm to 25 cm and then location of the critical section has moved towards the upstream side from 8.1 to 4.7 cm, 7.1 to 4.9 cm, 8.3 to 5.0 cm under free flow 60 per cent, 75 per cent submergence conditions, respectively. Crest height has increased from 10 cm to 25 cm and then location of the critical section has moved towards the upstream side from 8.4 to 6.0 cm, 8.6 to 6.1 cm, 6.3 cm for 6 Ls^-1 discharge under free flow, 60 per cent, 75 per cent submergence conditions due to increased the contact surface and friction and not found for 90 per cent submergence levels for all the four weirs.

Keywords

Hydraulic Flume, Semi-Circular Crested Weirs, Characteristics of Semi-Circular Weirs, Open Channels, Point Gauge, Critical Depth, Crest Height, Discharges.

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