Design of irrigation structures

The old irrigation hydraulic structures along the Nile and its main branches face the problems of operation, aging, ill maintenance and the desire to extend its lifetime. Economically, building a new one is not feasible. Furthermore, the operation of the irrigation system changed dramatically after building the High Aswan Dam and new design codes replaced the old design methods. Upgrading and enhancing old masonry hydraulic structures in Egypt is an extreme necessity and traditional solutions are not compatible with the operational requirements. For a reason or another, several structures such as Assuit and Zefta barrages have been remodeled. Upgrading and renovating constitute several studies and structural solutions that are not commonly available and has to be taken as a case by case matter, and the literature does not support such cases well.

This paper presents several upgrading solutions for an old regulator, where not all methods are convenient. A study of the different methods is presented and analyzed.

In this study, the operational and design performance of the main canal (MC) was assessed to determine the carrying capacity of water delivery during peak irrigation requirement using selected performance indicators. The performance indicators used were water delivery ratio, relative changes in water level (RCWL) and canal design capacity ratio. The study was carried by collecting data comprising flow discharges and canal water level at selected locations in the MC conveyance system. The climate data and the crop growth parameters were used to determine the peak irrigation requirement (Q R). The peak of irrigation requirement estimated for the entire commands of the East-bank canal was 5.68 m 3 s −1 during February. The results revealed that the designed flow discharge of the canal was sufficient to meet the present irrigation demands of the estate. However, the actual water delivery performance of the canal was lower as it was below 70.5% at downstream. RCWL estimated at the tail reach of the canal was 23.3% indicating a substantial reduction of canal flow depth at downstream. Lastly, it was concluded that the entire water conveyance system of the canal needs to be modified for improvements. ARTICLE HISTORY

The dimensions of many water streams, which satisfy proper hydraulic conditions, may not be compatible with the designed dimensions of an irrigation work that needs to be constructed in some locations. The design requirements of such irrigation works may involve a contraction in the channel width in the required location. This contraction, of course, affects different flow properties and the scour hole formed downstream of these structures. Therefore, the present experimental study aims to investigate the effect of the transition angle and the contraction on the flow properties and on the scour phenomenon downstream water structures. Through 460 experimental runs, carried out on 20 experimental models, the study proved that, for an efficient hydraulic performance and economic design, the best transition angle (θ) for the approaches of water structures is 30° with a relative contracted width ratio (r = b/B) not less than 0.6.