A high phraetic line within an earthfill dam would indicate which of the following?

• A. A potential problem with seepage nearing the surface which would cause problems with erosion or slope failure of the surface materials of the dam
• B. Seepage issues with no surface expression
• C. Sufficient seepage to reinforce the dam
• D. No impact on dam stability

Answer: (A)

The main idea tested is how the position of the phreatic (seepage) line inside an earthfill dam relates to surface stability and erosion risk. A high phreatic line means seepage is close to the surface, so pore pressures in the upper zones are elevated and the surface materials are saturated. This situation can lead to surface erosion and slope instability of the dam’s face or crest, as flowing water undermines the surface materials and can initiate cracks, slides, or even internal erosion (piping) that compromises stability. Therefore, a high phreatic line signals a potential problem with seepage nearing the surface, requiring protective measures or drainage to prevent surface deterioration. The other scenarios—seepage with no surface expression, seepage sufficient to reinforce the dam, or no impact on stability—do not match the consequence of seepage being near the surface.