Steady State vs. Transient Modeling

Steady State vs. Transient Modeling

   Groundwater flow models describe their capabilities as either steady state and/or transient.  It is important when deciding upon groundwater modeling software to know which options are necessary for your needs.  This month's newsletter will describe the key differences between steady state and transient modeling.

   Steady state flow occurs when the magnitude and direction of flow is constant with time throughout the entire domain.  Conversely, transient flow occurs when the magnitude and direction of the flow changes with time.  In other words, the hydraulic head doesn't change with time in a steady state flow system, but does change during transient flow. This does not mean that in a steady state system there is no movement of groundwater, it simply means that the amount of water within the domain remains the same, and that the amount of water that flows into the system, is the same amount as flows out.

   The steady state flow conditions simplify the groundwater flow equation significantly. When steady state flow occurs, time is no longer an independent variable and thus the storage term in the groundwater flow equation disappears; since there is no change in the amount of water within the domain (no change in hydraulic head) there is obviously no change in the amount of water stored in the domain.  

  References:

 Fetter, C.Q. (1994). Applied Hydrogeology. Published by Maxwell Macmillan International, New York.

Freeze, R.A, and Cherry, J.A. (1979). Groundwater. Published by Prentice Hall, Inc., New Jersey.