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20 ■ Chapter 3 Dams, Locks, and Bridges Boat and PWC operators may encounter physical structures such as dams, locks, and bridges. You need to be extra cautious in these situations. Dams Dams pose dangers both above and below the dams. ◆ The low-head dam is the most dangerous type of dam and has been named the "drowning machine." They may not be easily spotted because the top of a low-head dam can be several feet below the water's surface. Because of their small size and drop, low-head dams do not appear to be dangerous. However, water going over a low-head dam creates a strong recirculating current or backroller (sometimes referred to as the "boil") at the base of the dam. Even on small rivers, the force of the backroller can trap your vessel against the face of the dam and pull you under the water—even while wearing your personal flotation device (life jacket). Be aware that on large rivers or during high water the backroller or boil may be located more than 100 feet downstream of the dam. Avoid low-head dams. ◆ Large-structure dams are more easily spotted because of their powerhouses and spillways. They can be dangerous to boaters and swimmers both below and above the dam. These areas are usually off-limits. Obey all warning signs and signals. Locks By learning how to use locks, you will have a host of new opportunities for pleasure boating on the rivers of North America. Lock attendants are present at most locks to help you through safely. ◆ A series of dams on a river help maintain enough water depth to allow river traffic to operate year-round. As a result of a dam, there will be two levels of water at the dam site—one level above the dam and a different one below. Locks safely transport boats from one water level to another, like an elevator. ◆ When approaching the lock: • Be aware that commercial traffic always has priority over recreational boats. • Wait at least 400 feet away from the lock for the signal to enter the lock. • Alert the lock attendant that you wish to go through the lock. You can sound one prolonged blast followed by one short blast of your boat's sound-producing device. You also may contact the lock attendant using your VHF marine radio on Channel 13, but never interrupt commercial communication. • Enter the lock only after you've been signaled to enter by the lock's traffic lights or by the lock attendant. Otherwise, stay well clear of the lock. ◆ When using locks, boaters should: • Have fenders and at least 100 feet of rope to use in securing your boat inside the lock. • Follow the lock attendant's instructions and proceed slowly. • Avoid passing another boat when inside the lock, unless directed to do so by the lock attendant. • Wait for the lock attendant's signal to exit the lock. Low-head dams pose a serious danger to vessel operators. Surface currents below low-head dams can suck vessels toward the face of the dam. Currents above low-head dams can sweep vessels over the dam. The recirculating currents and turbulent waters below these dams can swamp vessels and drown boaters. Traffic Signal Lights at Locks Flashing red light means stay well clear of the lock and do not enter. Allow plenty of room for boats to exit the lock. Flashing amber light means approach the lock at a safe speed and under full control. Flashing green light means enter the lock. Rear gate opens and boats enter lock Gate closes and water level adjusts Front gate opens and boats exit lock Boil Backwash Low-Head Dam Copyright © 2014 Boat Ed, www.boat-ed.com

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