Contents preface (VII) introduction 1—37

Side elevation
253

24 24 24

223

Plan

152

76

253

177
128 253

Front elevation

Fig. 10.8 Arrows

360 IRRIGATION AND WATER RESOURCES ENGINEERING
The length of cistern required to be roughened is equal to (1)

_c h₃^{3 /2} H_L^{1/ 2}




D
where, D is the depth of water in the cistern, h₃ the depth of flow in the downstream channel, H_L the drop height and c is a coefficient whose value depends on the type of impact as follows:
Vertical impact, c = 1 Horizontal impact, c = 3 Inclined impact with baffle, c = 4
Inclined impact without baffle, c = 6 No impact, c = 8 to 10

Where hydraulic impact occurs, the roughening should start downstream of the jump at a distance about half the height of the hydraulic jump. Downstream of the roughened length, a smooth cistern (without roughening devices) about half as long as the roughened cistern should be provided (1).