1&2 Introduction
Educational Objectives
3 The Boat
Terminology
Boat Types
Measuring Length
Hull designs
Types of hulls
Propulsion
Carbon Monoxide
Capacity Plate
Engine Systems
Checklist
Review Quiz - 3
4 Legal Requirements
Who May Operate
Registration and Numbering
Hull ID Number
Required Equipment
Personal Flotation Devices
Navigation Lights
Fire Extinguishers
Ventilation
Backfire Flame Arrestor
Sound Producing Device
Visual Distress Signals
Pollution Regulations
MSDs
No Discharge Zones
Aquatic Nuisance Species
Recommended Equipment
Review Quiz- 4
5 Preparation
Vessel Check List
Trailering
Environmental Conditions
Leeway
Tide and Current
Local Hazards
Float Plan
Preventive Maintenance
Fueling
Review Quiz-5
6 Operations
Operator responsibility
Homeland Security
BUI
Navigation Rules
Definitions
Proper Lookout
Seamanship
Sound Signals
Rules of the Road
Meeting & Crossing
Commercial Vessels
Restricted Visibility
Aids to Navigation
Review Quiz-6
7 Getting Underway
Line Handling
Docking/Undocking
Maneuvering Underway
Anchoring
Water Sports
Hunting and Fishing
Swimming
Diving and Snorkling
Paddle Sports
Skiing and Towing
Personal Watercraft
Review Quiz-7
8 Accidents
Fatal Vs Non-fatal
Accident Reports
Crew Overboard
Assistance from Shore
Hypothermia
Fires on Board
First Aid
Rendering Assistance
Running Aground
Review Quiz-8
9 Special Items
Vessel Repairs
Locks
Dams
Security
Sailing
Review Quiz-9
State Requirements
Final Exam

Chapter IX - Special ItemsSection 3 - Dams

Dams

Dams are built to back up water in a reservoir for a variety of reasons. Dams are hazardous both above and below the dam. These wall-like structures pool the water as it flows over the crest and drops to the lower level.

This drop creates a hydraulic, which is a backwash that traps and re-circulates anything that floats. Boats and people have been caught in this backwash. A person caught in the backwash of a low-head dam will be carried to the face of the dam, where the water pouring over it will wash him down under to a point downstream called the boil. The boil is that position where the water from below surfaces and moves either downstream or back toward the dam. A person who is caught in a low head dam struggles to the surface, where the backwash once again carries him to the face of the dam, thus continuing the cycle

.

To complicate matters, these dams are usually loaded with debris, such as tires and logs on the surface and rocks and steel bars just below, posing additional problems should a person get trapped in this dangerous structure.

Dams do not need to have a deep drop to create a dangerous backwash. During periods of high water and heavy rains, the backwash current problems get worse, and the reach of the backwash current is extended downstream.

Small low-head dams that may have provided a refreshing wading spot at low water can become a brutal death trap when river levels are up. Simply put, it is not the drop of the dam which is the lethal danger, but the backwash current. This backwash current is governed by volume of water and flow.

From downstream, you may not realize the danger until it’s too late. From upstream, low-head dams are difficult to detect. In most instances, a low-head dam does not look dangerous, yet can create a life-threatening situation. You should always pay attention to warning signs, markers or buoys and keep well clear of low-head dams.

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