Illustration of hyrdologic cycle. i.e. rainfall, surface water, surface runoff, water table, groundwater flow, etc.

Figure 4. Typical hydrologic cycle for eastern North Carolina. East of I-95 (which parallels the fall line between the coastal plain and the piedmont) average annual rainfall ranges from 46 to 56 inches, depending on location. Actual evaporation ranges from 34 to 36 inches annually.

Illustration of hyrdologic cycle. i.e. rainfall, surface water, surface runoff, water table, groundwater flow, etc.

Therefore, the "excess" rainfall, most of which returns to surface waters, ranges from 12 to 20 inches per year.