# EPA On-line Tools for Site Assessment Calculation

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The gradient calculators either fit a line or a plane to the water surface.

How often is the water table a straight line or plane? Only if flow is

- one-dimensional
- confined

Since the curvature is often slight, a planar or straight-line approximation is acceptable. Although there might not be much deviation from a straight line locally, over long distances the differences become significant. Also as flow approaches a discharge point, the gradient may steepen as the velocity increases. A single gradient for the whole flow system is no longer appropriate.

The water table also is curved- in three dimensional flow
- because of locallized mounding
- because of pumping or injection wells

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