A | Cross-sectional area of the pipe or tunnel |

A | Cross-sectional area of surge tank in the water surface |

D | Diameter of pipe or tunnel |

D | Width of water surface in the surge tank |

D | 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 |

Z | 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 | Maximum level of the water surface in the surge tank |