A

Cross-sectional area of the pipe or tunnel

A_s

Cross-sectional area of surge tank in the water surface

D

Diameter of pipe or tunnel

D_s

Width of water surface in the surge tank

D_s0

Diameter of the base of the surge tank

f

Darcy-Weisbach friction factor

g

Acceleration of gravity

L

Length of pipe or tunnel

m

Side slope in surge tank cross-section

Sum of the coefficients for all minor losses in the pipe or tunnel

t

Time

V

Water velocity

Z₀

Water level in the surge tank below reservoir level in the case of steady flow condition

Z⁻

Water level in the surge tank below reservoir level

Z⁺

Water level in the surge tank above reservoir level

Z_max

Maximum level of the water surface in the surge tank