الفهرس | Only 14 pages are availabe for public view |
Abstract An appropriate flow resistance value is obtained from field measurements. For a specific flow rate, wetted area and fall in head over a certain distance, the flow resistance was commonly calculated by one of the famous flow formulas like Manning’s formula. The net cross-section was used for the wetted area and the hydraulic radius. The result is a roughness coefficient, such as n, which represents mainly the roughness on the wetted perimeter . The flow formulas were originally derived for sections with little to no obstruction elements present, such as concrete lining or large alluvial channels . However severe weed growth reduces the effective flow area considerably and the flow velocity within the vegetated part is considerably neglected . Therefore it has been assumed that the obstructed part has no effect on the discharge capacity. According to the above assumption, analysis process has been applied on collected field measurements along two main vegetated canals suffering from submerged weeds in upper Egypt in order to achieve the best design and performance of grassed open channels. Also to help irrigation engineers in detecting the most suitable time of maintenance program for the vegetated open channels depending on what efficiency is needed. Through this study, it was assumed that the flowing discharge passes only through the net area free of weeds. So open channel dimensions were calculated for the net area of the cross-sections free of weeds. It has been calculated a net hydraulic radius, a net hydraulic mean depth, and new open channel dimensions that calculated for the net cross-section area. Then Manning’s equation has been used to calculate the canal dimensions in case of no vegetation then in case of vegetation growth for different weed densities. Also the hydraulic efficiency has been calculated to study the effect of weed growth and the change in channel dimensions on the flow efficiency. |