hydraulics engineering engr. muhammad hassan [email protected]
TRANSCRIPT
Best Hydraulic Channel
Objective of Channel Design
• Transport of water between two points in a safe and cost effective manner.
• Includes economical safety and aesthetic aspects.
• The channel having the least wetted perimeter for the given area has the maximum conveyance.
• Only focus will be on hydraulic aspects. Conveyance of a channel increases with hydraulic radius (Manning’s Formula).
• Hydraulic radius increases with a decrease in wetted perimeter.
• Best hydraulic section is the one having minimum wetted perimeter.
• For a specific cross section, the proportion that produces the best hydraulic cross section (maximum flow) might be derived.
• The best hydraulic section might not be best from economical point of view.
• The minimum permissible velocity is the lowest velocity that will prevent sedimentation and vegetative growth (0.6 to 0.9 m/s for sedimentation and 0.75 m/s for vegetation.
• The vertical distance from the top of the channel to the water surface is known as freeboard.
Assignment
• What about trapezoidal channel?• What about circular channel?
Practice
• For a trapezoidal channel with base width 6.0m, side slope 1:2(V:H) , and n=2 , calculate the critical depth, critical velocity, and critical slope for Q= 17cumecs.
• A rectangular channel is 3m wide, has a 0.01 slope, flow rate of 5.3 cumecs , and n=0.011. find the normal and critical depths of flow.
• Water flows in a rectangular channel at a depth of 1.22 m and flow rate of 5.66 cumecs. Determine channel width if the channel is sub critical.
• For a trapezoidal channel with base width b=3.0m , Manning's n=0.025 and side slope of 1V:2H, calculate the critical depth, critical velocity and critical slope if Q=10 cumecs.