Gates Gates Gates are used to control the

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Gates

Gates

Gates • Gates are used to control the discharge and also to stop the

Gates • Gates are used to control the discharge and also to stop the flow if required. y 1 w y 2

 • The discharge can be evaluated according to the condition of the water

• The discharge can be evaluated according to the condition of the water under the gate. If the flow is supercritical i. e. • Then, the discharge can be calculated as follows;

 • Where: q is the discharge per unit width =Q/b g acceleration of

• Where: q is the discharge per unit width =Q/b g acceleration of gravity = 9. 81 m 3/sec Yc critical depth Ce discharge coefficient (from graph) b Channel width A is the water section = b w w is the opening height of the gate

Ce

Ce

 • In case of subcritical flow, no jump, the flow can be evaluated

• In case of subcritical flow, no jump, the flow can be evaluated as follows; Where, Cd is discharge coefficient = 0. 61

 • Example • For a maximum discharge of 12 m 3/sec in a

• Example • For a maximum discharge of 12 m 3/sec in a channel of width 14 m, upstream water depth of 2. 2 m and downstream water depth 1. 6 m, design the gate opening? Sol. First assume subcritical flow, Apply the equation get A = 5. 73 m 2 then w = 5. 73/14 = 0. 41 m

Check for critical flow Yc = 0. 42 m > w Then assumption is

Check for critical flow Yc = 0. 42 m > w Then assumption is wrong Apply the equation for the supercritical flow; assuming w = 0. 41 m Then y 1/w = 5. 4 and y 2/w = 3. 9 get Ce = 0. 4 get A = 4. 6 m then w = 4. 57/14 = 0. 32 m

Then y 1/w = 6. 9 and y 2/w = 5 get Ce =

Then y 1/w = 6. 9 and y 2/w = 5 get Ce = 0. 38 get A = 4. 81 m then w = 4. 81/14 = 0. 34 m Again Then y 1/w = 6. 5 and y 2/w = 4. 7 get Ce = 0. 39 get A = 4. 68 m then w = 4. 68/14 = 0. 33 m Close … then w = 0. 33 m