Table 1

1 January 2000

Table 1: Assumptions employed in the guides on optimum diameter of diversion tunnel

Type	Top width, B (m)	Average length, W(m)	Average side slope	Freeboard, F (m)
Embankment	5	100 to 1200	1H:2.25V	1.5
Length, L (m)	Diameter, D (m)	Longitudinal slope, S (-)	Lining thickness, T(cm)
100 to 1400	3 to 15	0.005 (0.001 to 0.015)	30 to 75, varying linearly with D
Discharge, Q (m3/s)	Manning Roughness Coefficient, n		Flow regime	Exit
50 to 1900	0.014 for RC lining	0.022 for shotcrete	0.030 for natural rock	Pressurised (full flow)	Unsubmerged
Type I (n=0.014	Type II (n=0.022)	Type III (n=0.030)	Rock bolts	Shotcrete
Rock bolts + Shotcrete + Reinforced concrete (RC)	Rock bolts + shotcrete	Little rock bolts + little shotcrete	~3m long	10cm thick with steel wires
Tunnel excavation, C1 (US$/m3)	Concrete lining C2 (US$/m3)	Support (rock bolts + shotcrete), C3 (US$/m2)	Fill for the cofferdam, C4 (US$/m3)
8 to 48	40 to 140	24 to 70	2 to 8

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