International Water Technology Journal, IWTJ Vol. 6–No.3 September 2016 195 A NEW EFFICIENT WATER ENERGY DISSIPATOR FOR IMPROVING THE IRRIGATION WATER QUALITY Mohamed A. Ashour 1 , Tawab E. Aly 2 , Tarek S. Abuzaid 3 1 Professor, Civil Eng. Dept., Assiut University, Egypt, mashour475275@yahoo.com. 2 Lecturer, Civil Eng. Dept., Assiut University, Egypt, tawab_aly@yahoo.com. 3 Assistant Lecturer, Civil Eng. Dept., Assiut University, Egypt, tareksayed1986@gmail.com. ABSTRACT The present experimental study was executed to investigate a new and untested shape of curved dissipators with different angles of curvature and arrangements from the following two points of view: (i) To examine its efficiency in dissipating the kinetic water energy; (ii) To examine the most effective shape and arrangement obtained from the abovementioned step in enriching the flow with dissolved oxygen for enhancing the irrigation water quality. The study was held in the irrigation and hydraulic laboratory in the Civil Department, Faculty of Engineering, Assiut University, using a bed tilting channel 20 m long, 30 cm wide and 50 cm height, using 20 types of curved dissipators with different arrangements. A total of 660 runs were carried out with different discharges. Results, in general, showed that, for the same angle of curvature, the dissipator performance is more tangible in dissipating the water energy when the curvature is in the opposite direction of the flow. Also, the energy loss ratio increases with the increase of the dissipator curvature angle (θ), till it reaches (120°), then it decreases again. The study also showed that using four rows of dissipators gives nearly the same effect of using three rows concerning both, the relative energy dissipation and dissolved oxygen content. So, it is recommended to use not more than three rows of the introduced curved dissipator with an angle of curvature equals (120°) in the opposite direction of the flow to obtain the maximum percentage of water energy dissipation downstream head structures and maximum dissolved oxygen content. Also, the study showed that, using the new introduced curved dissipator in three rows in the staggered-separate manner gives the best formed hydraulic jump characteristics, less relative depth and less relative length than all other tested dissipators, which reduces the cost of construction of the solid apron on the downstream side of head structure. Keywords: Energy dissipation, Water quality, Dissolved oxygen, Aeration, Curved sill dissipater Received 10 May 2016.Accepted 6, July 2016 Presented in IWTC 19 th 1 INTRODUCTION The prime goals of this research are, saving, controlling, and improving the quality of the available quantity of water for irrigation. Since saving and controlling of irrigation water can be achieved through some storage and diversion head structures like dams, regulators and weirs, which cause many destructive problems thatmust be treated to avoid the probable failure of the head structure. At the same time, such structures change the water hydraulic regime behavior owing to raising the upstream water level, gaining a great potential energy, which converts into kinetic energy through falling over the head structure, and produces a large number of eddies and bubbles. These air bubbles entrained in the flow, not only increase the dissolved oxygen content in the water flow, but also prevent the cavitation in highspeed flows downstream head structures. Therefore, with regards to the danger of cavitation attack, forcing aeration of flow is recommended, (Flavey, 1990;Pionto, 1991). Such falling generatesa hydraulic jump in the downstream side which must be overcome shortly and as close as possible to the head structure, to keep the structure and its solid apron safe. The most effective method for accelerating the formation of the hydraulic jump to dissipate the falling water energy is using some types of energy dissipators with different shapes and with different arrangements on the solid apron at the downstream side of the structure. The literature on such a topic is rich with many studies for many