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Elements overview

The analytic elements used in Anaqsim include the elements described in the following references:

Wells

The standard well element described by Strack (1989) is used in isotropic subdomains and the well element of Fitts (2006) is used in anisotropic subdomains.

There are three possible kinds of pumping wells in Anaqsim:

  1. Discharge-specified wells in just one subdomain. With this type of well, you specify the known discharge of the well.
  2. Discharge-specified wells spanning multiple subdomains. This is for wells that are screened across multiple levels and subdomains in a multi-level part of a model. For example, a well could be screened across the two lowest levels in a 4-level part of a model. You specify the known discharge of the well, and Anaqsim imposes these conditions: (a) the heads at the well radii in each screened subdomain are identical, and (b) the total discharge of the well elements in the screened subdomains equals the specified discharge of the well.
  3. Head-specified wells in just one subdomain. With this type of well, you specify the known head at the well radius. Anaqsim determines the discharge needed to meet this condition.

Line boundaries

Line boundaries are represented by high-order line elements similar to those described by Janković and Barnes (1999). Line elements are either linesinks, line dipoles, or line doublets. Line elements may have up to ten unknown parameters (degrees of freedom). For example, a linesink with one parameter has a constant discharge/length along its length, a linesink with two parameters has discharge/length that varies linearly along its length, and a linesink with three parameters has discharge/length that varies parabolically along its length. Strack (1989) gives a good overview of line elements.

Uniform area source/sinks

Uniform area source/sinks (constant over a subdomain) are modeled with the uniform recharge functions described by Strack (1989). For these, the extraction/area is uniform over the entire subdomain. This is appropriate in cases with a single level, steady flow, and a uniform recharge rate or zero recharge.

Spatially-variable area source/sinks

Spatially-variable area source/sinks are modeled with the multi-quadric radial basis function elements described by Strack and Janković (1999). With these, the extraction/area varies with location. Spatially-variable extraction occurs when the extraction = recharge + leakage + transient storage flux is spatially variable. This is generally the case in multi-level models where spatially-variable leakage occurs and in transient models where spatially-variable storage flux occurs. See Recharge, leakage and storage and Fitts (2010) for details of how these elements are used to represent recharge, leakage and storage flux.