At McAlpine L & D, normal upper pool elevation is 420.0 feet MSL, equal to 12.0 feet on the upper gage. The vertical clearance at the Clark Memorial Highway bridge is 72.6 feet above normal pool. What is the clearance if the gage reads 27.2 feet?

Correct Answer: Option C — 57.4 feet

The gage reads 27.2 feet, which is 15.2 feet above the normal pool of 12.0 feet (27.2 - 12.0 = 15.2). Subtracting this rise from the original clearance of 72.6 feet yields 57.4 feet. This calculation accounts for the increased water level reducing the available vertical clearance under the bridge.