FE Civil Practice Question Solution included after investigation
CASE E-112 · FE

The Aquifer That Moved 1,500 ft³/day, Not 72,000

The hydraulic gradient was correct, but the plan-view area was used instead of the area perpendicular to groundwater flow. The aquifer moved 1,500 ft³/day.

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Case E-112 engineering failure visual
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1

Inspect

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2

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3

Prove

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4

Fix

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5

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Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

A confined aquifer has hydraulic conductivity K=30 ft/day, saturated thickness b=25 ft, and width perpendicular to flow W=400 ft. Hydraulic head drops 6 ft over a flow length of 1,200 ft. Determine discharge using Darcy's law Q=KiA.

Water Resources Environmental Engineering Civil Design Verification Root Cause Analysis Safe Correction
E-112
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

Plan area was used as Darcy flow area.

What was missed

Flow area must be normal to the groundwater direction.

Corrected model

Use Q=KiA with i=Δh/L and A=bW for the stated confined aquifer.

QUICK ANSWER

i=6/1200=0.005 and A=25×400=10,000 ft². Therefore Q=KiA=30(0.005)(10,000)=1,500 ft³/day.

ENGINEERING TAKEAWAY

Use Q=KiA with A equal to saturated thickness times width for horizontal confined flow.

CASE QUESTIONS

Questions this case should settle.

What area is used in Darcy's law for horizontal confined flow?

The saturated thickness times width, normal to the flow direction.

NEXT FE PRACTICE QUESTION

The Basin That Needed 12,600 ft³, Not 21,600

Water Resources Environmental Engineering · 5–10 min

Continue Practice →
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Each case is designed to build the judgment, analysis, and confidence you need for engineering exams — and beyond.

  • Apply core engineering concepts to real-world problems
  • Practice structured troubleshooting and analysis
  • Strengthen exam-ready thinking through realistic scenarios
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