How can groundwater flow direction be determined at a site?

• A. By measuring rainfall intensity
• B. By analyzing soil color
• C. By measuring hydraulic heads across wells and using gradient analysis; mapping head contours indicates flow direction
• D. By measuring surface temperature

Answer: (C)

Groundwater flow follows the hydraulic gradient, moving from higher hydraulic head to lower hydraulic head. To determine flow direction at a site, measure hydraulic heads at multiple wells across the area, ideally during the same groundwater conditions. Use those head values to compute the gradient between locations and plot head contours (equipotential lines) on a map. The flow direction is perpendicular to these contours, from high head toward low head, which aligns with Darcy’s law that relates flow to the gradient.

Rainfall intensity tells you about recharge, not the current direction of groundwater movement. Soil color doesn’t indicate the subsurface hydraulic gradient, and surface temperature reflects near-surface conditions rather than subsurface flow.