🔍 Key Concepts

• Vertical clearance is the distance from the water surface up to the lowest part of the bridge structure. • On inland rivers, published bridge clearances are usually given at a reference gage height (often 0.0 or a specific stage). • To solve, you need to adjust the charted bridge clearance using the current gage reading before comparing it with your towboat height.

💭 Think About

• Think about how the gage reading affects the clearance: if the river is higher than the reference stage, does the clearance increase or decrease? • What information do you need from the river tables or bridge list about the Helena Highway Bridge to start the calculation? • Once you adjust the bridge clearance for the current gage, how do you figure out whether your 53-foot towboat will fit and what the remaining clearance is?

✅ Before You Answer

• Be sure you understand whether the published bridge clearance is given at 0.0 gage or at a specific stage on the Helena Gage. • Carefully apply the difference between the reference gage and the current gage (6.7 ft)—including the correct sign (add or subtract). • After finding the adjusted bridge clearance, subtract your 53 ft air draft to find the remaining vertical clearance, then match that to the closest choice.