Zone of Influence vs. Zone of Contribution

Hydrogeologically, the WHPA is essentially the contributing area (or zone of contribution) to a well and it should not be confused with the zone of influence which is the aerial view of the cone of depression (see the chapter on Basic Principles). This activity illustrates the shortcomings of using the zone of influence as the WHPA.

Activity: The zone of influence (ZOI) versus the zone of contribution (ZOC). Using the ZOI as a WHPA will overestimate the area in the downgradient direction and underestimate it in the upgradient direction.