*A* |
cross-sectional area perpendicular to flow (L^{2}) |

*α* |
compressibility of the aquifer skeleton (T^{2}LM^{−1}) |

*β* |
compressibility of water (T^{2}LM^{−1}) |

*C* |
concentration in the stream water (ML^{−3}) |

*C*_{g} |
concentration in 100% groundwater (ML^{−3}) |

*C*_{r} |
concentration in 100% surface runoff water (ML^{−3}) |

*D* |
in Equation 2, mean pore size diameter for porous media or the pipe diameter (L) |

*D* |
in Equation 4, hydraulic diameter of the pipe (L) (for circular pipe it is the pipe diameter, but for a non-circular pipe D = 2 times the square root of (A/π); where A is the cross-sectional area) |

Δ*h* |
measured head difference (L) |

Δ*l* |
length over which the head difference is measured (L) |

Δ*p* |
pressure difference between two ends of the pipe (ML^{−1}T^{−2}) |

*f*_{D} |
Darcy friction factor (dimensionless) |

*g* |
local acceleration due to gravity or gravity constant (LT^{−2}) |

*K* |
hydraulic conductivity of the porous medium (LT^{−1}) |

*L* |
pipe length (L) |

*μ* |
absolute or dynamic viscosity of water (ML^{−1}T^{−1}] |

*n* |
porosity (dimensionless) |

*ν* |
kinematic viscosity of water (L^{2}T^{−1}) |

*Q* |
volumetric discharge (L^{3}T^{−1}) |

*q* |
specific discharge (LT^{−1}) |

*Q*_{g} |
groundwater portion of the total discharge of the stream (L^{3}T^{−1}) |

*Q*_{r} |
surface runoff portion of the total discharge of the stream (L^{3}T^{−1}) |

*r* |
pipe radius (L) |

*Re* |
Reynolds number (dimensionless) |

*ρ* |
density of water (ML^{−3}) |

*S*_{s} |
specific storage (L^{−1}) |

*V* |
*Q/A* and is the mean flow velocity (LT^{−1}) across a cross sectional area (also called Darcy velocity), which is equal to the volumetric flow, Q (L^{3}T^{−1}), divided by the cross-sectional area perpendicular to the direction of flow, *A* (L^{2}) |