Effect of Reliability of Water Releases Downstream Abu Ushar Head Regulator, Gezira Scheme, Sudan

Abstract

Reliability of water releases is of essential importance, as it is the basis of water delivery scheduling as well as water resources planning and management. This study was conducted in Abu Ushar head regulator of Gezira Main Canal, Gezira Scheme (GS) at 169 Km from Sennar Dam. The main objective was to study reliability of water releases downstream Abu Ushar head regulator. This regulator serves irrigation water operation of the North GS. It consists of a number of canals namely Turabi, North West Branch, Abu Ushar Major, Debaba Major, Baranco Minor, Tatai Minor, Wad Elmagdi Minor and Abu Ushar Scape. The field work was conducted by measuring water levels during the period from 1st Oct. to 31th Dec. 2005 at the control structures of the canals under study. Also, the openings of the gates and the heads over weirs were daily measured to calculate the discharges passing through the investigated canals by using the corresponding equations. The study showed that the average difference between the recorded discharge (QR) and the calculated discharge (QC) was (0.4%) for Turabi, and (0.1%) for North West Branch. The small differences between calculated and recorded discharges were attributed to the adoption of appropriate discharge equations by the irrigation authority. This is also valid for Abu Ushar (4.6%) and Debaba (4.4%) majors. It was found out that there was disagreement between the recorded and measured discharges in the case of the minor canals. The study gave differences in order of 25.6%, 23.6% and 16.7% for Baranco,Tatai and Wad Elmagdi minor canals, respectivly. This could be attributed to the deterioration of gates and weirs, which led the irrigation authority to adopt constant daily rates of 10,000 m3 (Baranco and Tatai) and 40,000 m3 (Wad Elmagdi minor).