FLOWTHRU displays groundwater flow patterns in an aquifer near a surface water body.  Although written with shallow lakes in mind, the program also applies to wetlands, rivers, streams, canals and channels.  The primary uses of FLOWTHRU are (i) for determining the depths of groundwater capture zones near shallow water bodies (analogous to the problem of wellhead protection), and (ii) as an educational tool, to allow users to visualise flow patterns near surface water bodies.

FLOWTHRU is based on a two-dimensional vertical section through water bodies which are long in the direction perpendicular to the direction of regional groundwater flow (Figure 1).  Depending on the directions of flow at lateral boundaries, FLOWTHRU applies to flow-through lakes (Figure 1a), to rivers or channels receiving water from both sides (Figure 1b), or to channels or elongated pits which provide recharge to the regional aquifer (Figure 1c).

FLOWTHRU recognises 17 flow-through regimes, as well as 11 recharge and 11 discharge regimes which can occur under different combinations of regional flow and recharge. It is important to understand that flow "regimes" are defined based on the directions of seepage through the bed of a water body, and can not be determined a priori based on the directions of flow at the boundaries of a vertical section.

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Figure 1a:   Flow near a long flow-through water body

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Figure 1b:   Flow towards a long water body from both sides

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Figure 1c:   Flow away from a long water body in both directions

FLOWTHRU displays groundwater flow patterns in a two-dimensional vertical section through a shallow surface water body. This representation is only valid if the vertical section is aligned with the direction of regional groundwater flow and if the water body is long in the direction perpendicular to that section.

FLOWTHRU assumes that water bodies are shallow relative to the thickness of the aquifer. The water body is represented as an infinitesimally thin layer of constant head lying at the top surface of the aquifer.

FLOWTHRU can be considered as a companion to a paper by Nield et al. (1994), which provides a general framework for classifying groundwater flow patterns near elongated surface water bodies.  Townley and Trefry (2000) extended these results to three-dimensional flow near flow-through lakes (Figure 2).  All the flow patterns identified by FLOWTHRU can also occur on the plane of symmetry through a circular lake.

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Figure 2:   Three dimensional flow near a circular flow-through lake

FLOWTHRU is not a numerical groundwater model, but rather, combines and displays a set of precomputed solutions.  These solutions were obtained using the linear triangular finite element model, AQUIFEM-N.  The solutions are provided as a set of unformatted files, for a range of lake geometries.

Numerous display options are possible in the standalone version of FLOWTHRU.   The user can choose to work in either non-dimensional or physical variables, to view equipotentials, streamlines and/or dividing streamlines, and to view or hide spatial distributions of piezometric head on specified flux boundaries.  The spatial distribution of seepage through the bottom of the surface water body can be displayed and written to an output file.  Graphical output can also be saved as files suitable for HP plotters and laser printers and PostScript laser printers.

Figure 3 shows two examples of graphical output from FLOWTHRU.   The online version of FLOWTHRU supports a combination of physical variables and non-dimensional ratios to define the situation of interest.

FLOWTHRU was developed by researchers at CSIRO, and forms the basis of research continued by CSIRO Land and Water.