Sediment Problems of Irrigation Canals: Field Studies to Assess the Changes in Canals Profiles and Cross Sections
Abstract in English:
Wadi Zabid is one of the main agricultural Wadis in the Tihama Plain. Wide ranges of crops have been cultivated such as cereals, vegetables, fruits, and some cash crops like cotton, sesame and tobacco. It has provided the country with high valued food basket as well as exporting to the neighboring countries. The government realized the importance of Wadi Zabid and started in 1979 constructing diversion works and canals to maximize the agricultural output of the Wadi. During the past twenty years of operations, sediment deposition in front of the diversion works and along the canal system posed serious threats to the project network. Sediment deposition caused many problems such as blocking the off take pipes and gates, raising canal beds and reducing canals slope, increasing the field levels and reducing canal flow capacity. This study would assess the changes in canal sections and profiles at which the present canal profiles and sections are drawn and compared with the canal profiles and sections of the previous years to provide sound basis for problems assessment. Laboratory experiments and sieve analysis were conducted to analyze canal bed samples in order to draw recent grading curves and compared it with the previous grading curves of the canals. This study exposed the fact that canal sections and profiles are changed greatly due to the accumulation of sediments in the upper reaches of the canals whilst equilibrium sections and profiles existed in the middle parts with section erosion in the lower parts of the canal reaches. It also indicated that greater sediments sizes were deposited in the canal upper reaches, which meant that canal behavior is changed and does not work as it was designed for.