Gates

Gates Gates are used to control the discharge and also to stop the flow if required. Gates are used to control the discharge and also to stop the flow if required. y1y1 w y2y2

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

Where: Where: q is the discharge per unit width =Q/b q is the discharge per unit width =Q/b g acceleration of gravity = 9.81 m 3 /sec g acceleration of gravity = 9.81 m 3 /sec Y c critical depth Y c critical depth C e discharge coefficient (from graph) C e discharge coefficient (from graph) b Channel width b Channel width A is the water section = b w A is the water section = b w w is the opening height of the gate w is the opening height of the gate

CeCe

In case of subcritical flow, no jump, the flow can be evaluated as follows; In case of subcritical flow, no jump, the flow can be evaluated as follows; Where, C d is discharge coefficient = 0.61

Example 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. 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 Y c = 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 C e = 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 Then y 1 /w = 6.9 and y 2 /w = 5 get C e = 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 C e = 0.39 get A = 4.68 m then w = 4.68/14 = 0.33 m Close … then w = 0.33 m