87 
trivial 
ietary ) 
wiron- 
odular 
visu 
el to a 
DUtput 
t scale 
ties of 
'stems 
n into 
3. and 
These 
ponse 
ential 
)orous 
nd 3D 
re soil 
ternal 
niconi 
diable 
tream 
DEMs 
raulic 
of the 
;ones ) 
vari- 
)de or 
. data 
to as- 
ments 
-25.4 pressure he ad 
oc 
9. 6 
Figure 1: Subsurface water velocities for a soil and groundwater contamination problem. The 
isosurface represents the water table, arrow length represents flow magnitude, and shading intensity 
represents pressure head. Discharge across the seepage face at the left boundary is clearly seen. 
having similar properties, such as a clay lens within a sandy aquifer. GIS are extremely useful in 
the processing and presentation of inputs for such distributed models. Land cover information, soil 
maps, remote sensing images, and data from meteorological stations can all be easily represented 
and manipulated within GIS. 
For subsurface features and for model inputs which change in time, scientific visualization tools 
provide functionality which is lacking or inadequate in GIS. For instance, standard visualization 
techniques can be used to display the initial moisture content of the soil as a 3D image. As 
another example, using 30-minute data from a network of rain gauges and meteorological stations, 
visualization software can be used to produce an animation of the spatially interpolated precipitation 
and evaporation patterns on a watershed over a simulation period of interest. 
The model outputs detailed information on the distribution and magnitude of pressure heads, 
soil moisture content, and water fluxes, calculated at the land surface and in the soil zone and 
underlying aquifer (Figure 1). During a storm-interstorm simulation, evaporative losses, overland 
flow, and subsurface runoff will occur in different regions of the catchment, and these zones will grow 
and shrink in response to variability in atmospheric inputs, topography, soils, and initial conditions. 
Surface saturation output processed in a GIS can be used, for instance, to identify catchment areas 
that are most susceptible to waterlogging. Scientific visualization techniques can be used to map 
the magnitude and direction of subsurface groundwater velocities, conveying information about the 
patterns of groundwater recharge and stream discharge in a watershed.