Mass Balance
A mass balance must be performed, and used along with Darcy's law, to arrive at the transient groundwater flow equation. This balance is analogous to the energy balance used in heat transfer to arrive at the heat equation. It is simply a statement of accounting, that for a given control volume, aside from sources or sinks, mass cannot be created or destroyed. The conservation of mass states that for a given increment of time (Δt) the difference between the mass flowing in across the boundaries, the mass flowing out across the boundaries, and the sources within the volume, is the change in storage.
Read more about this topic: Groundwater Flow Equation
Famous quotes containing the words mass and/or balance:
“... in the happy laughter of a theatre audience one can get the most immediate and numerically impressive guarantee that there is nothing in one’s mind which is not familiar to the mass of persons living at the time.”
—Rebecca West (1892–1983)
“Bourgeois society is infected by monomania: the monomania of accounting. For it, the only thing that has value is what can be counted in francs and centimes. It never hesitates to sacrifice human life to figures which look well on paper, such as national budgets or industrial balance sheets.”
—Simone Weil (1909–1943)