BOUNDARY FLUX EXAMPLE #2 - NO FLOW

Example of Potential Problems Which May Result From Misunderstanding / Misusing a No Flow Boundary

When a no flow boundary is used to represent a ground water divide, drawdown may be overestimated, and although the model does not indicate it, there may be impacts beyond the model boundaries.

Figure 1

Simplified model with no-flow boundary representing the ground-water divide.

Figure 2

Use of a no-flow boundary in this manner may cause problems: When a ground water divide is defined as a no-flow boundary, the flow system on the other side of the boundary cannot supply water to the well, therefore predicted drawdowns will be greater than would be experienced in the physical system. The no-flow boundary prevents the ground water divide from shifting, implying there drawdown is zero on the other side of the divide.

Figure 3

Lesson: Monitor head at no flow boundaries used to represent flow lines or flow divides to ensure the location is valid even after the stress is applied.