Introduction
to Basic GroundWater Flow


By
the earthDr!


Analogy of the Flow of Rainfall Runoff to GroundWater Flow  
Groundwater
flow is a little more difficult to understand than is the flow of water
as sheet flow during or just after a rainfall. Let's start with flow
of water over the surface of hilly terrain to begin to understand
groundwater flow. The figure belowleft depicts hilly terrain in a 3dimensional
perspective. Even on hilly
Sometimes multiples of a 1foot contour is done. Since the grade at the surface of the water table is often so flat (limited grade or hydraulic gradient  not steep), a contour of the water table is often constructed in some multiple of 0.01 foot (1 foot rise in 100 foot run) or sometimes 0.001 (1 foot rise in 1,000 foot run) for a very flat water table. However, contours of the water table in multiples of 5 and 10 feet can be practible where there is significant relief (elevation change) such as in more mountainous terrain. Contouring in multiples of 0.01 foot would not be practicable for mountainous terrain to describe either surface relief or the surface of the water table since this would involve an inordinate number of contours being constructed for the steep slopes. In the first figure, contour lines are constructed in multiples of ten. The contour lines run from a 60foot to 100foot elevation above mean sea level. Remember that the contour line join points of equal elevation. Therefore, any point along the 70foot contour line should be at an elevation of 70 foot. A 3dimensional plot of contour lines, while it illustrates the concept of a line joining points of equal elevation, is not as useful a tool as a topographic map where contour lines are depicted in plan view as in the figure to the left. In a 3dimensional plot, higher elevations in the foreground can obscure contour lines in the background, thus, limiting its use. This figure in plan view is just the view from above of the first figure, which is displayed in 3 dimensions. Plan view (a view from above) is just the most convenient perspective to view the topographic relief as illustrated in the 3dimensional view above. It won't take you long to get accustomed to conceptualizing a plan view, which is in 2 dimensions, in 3 dimensions. 

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