Determination of Optimal Section and Hydraulic Characteristics of PrecastConcrete Channels (Canalette)

Nowadays, the use of precast concrete channels (canalette) has been considered due to its focus on manufacturing, possibility of high quality and quantity control in different stages of construction, as well as high speed of their production and operation. Despite three decades of production archaism and canalette installation in Iran, old regulations are used for design of different types. In this study, initially, with regard to the implementation and operation of canalettes, some definitions were developed for optimal section of this system. Then, it was determined that semi-elliptical cross-section with a ratio of small to large diameter of 0.436 is optimal section of the canalette. A comparison between optimal section of canalette and semi-circular cross-section represented canalette priority to reduce evaporation up to 34% compared to the semi-circular cross-section against an increase of 13 percent in consumed concrete. This is of higher priority especially in areas with high evaporation of water. Also, by determining the geometric characteristics of the channel with incomplete half- ellipse section (with free board), the explicit equations were presented for determining the critical and normal depths in a channel with half-ellipse section. The proposed equations exhibit both simplicity and high accuracy, having maximum relative error of less than 1.4%.