The Greenville Gage reads 1.6 feet. The high point of your towboat is 54 feet above water. What is the vertical clearance as you pass under the Greenville Highway Bridge?
• How river bridge clearances are typically published relative to a reference gage reading • How to adjust a charted bridge clearance when the actual gage reading is higher or lower than the reference • Relationship between water level change and available clearance under the bridge
• Ask yourself: If the river level goes up, does the clearance under the bridge increase or decrease? What about if the level goes down? • Think about what additional information you would normally need: a charted clearance at a standard gage level. How would you combine that with the 1.6-foot reading and your 54-foot air draft? • Compare each choice with the height of your vessel (54 feet). Which answers would mean you cannot safely pass, and which would allow safe passage with some margin?
• Be clear whether the gage reading is telling you how high the water is, not the clearance itself • Check that the vertical clearance must be greater than your 54-foot air draft to pass safely • Verify that any computed clearance must make physical sense compared with a typical highway bridge over an inland waterway (not unrealistically low or high)
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