Calculate the effective length of the spillway which consists of 6 spans having a clear width of 10 m each. The thickness of each pier may be taken as 2.5 m and the total design head on the crest including velocity head is 16.3 m. Assuming 90° cut water nose piers and rounded abutments.

Calculate the effective length of the spillway which consists of 6 spans having a clear width of 10 m each. The thickness of each pier may be taken as 2.5 m and the total design head on the crest including velocity head is 16.3 m. Assuming 90° cut water nose piers and rounded abutments. Correct Answer 55 m

The effective length of the spillway is given by- Le = L – 2.H Where L = clear length of the spillway crest = 6 x 10 = 60, N = Number of piers = 5 and H = 16.3 m For 90° cut water nose piers and rounded abutments; Ka = 0.1 and Kp = 0.01 Le = 60 – 2 x 16.3 = 55.1 m.

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The discharge passing over an ogee spillway is given by (where, L is effective length of spillway crest and H is the total head over the spillway crest including velocity head.)
Statement (I): The ogee spillway is a control weir having an S-shaped crest profile which provides a high discharge coefficient without causing cavitations. Statement (II): The crest profile of ogee spillway conforms to the lower nappe of flow over a ventilated sharp-crested weir and ensures a constant discharge coefficient for all heads.