NAUI Master Scuba Diver 34 The Diving Environment LEARNING GOALS In this chapter, you will: 1. Be introduced to the environmental terms presented in bold letters. 2. Identify the following terms: waves, surge, surf, tides, seiches, currents, thermoclines, haloclines, bottom composition, weather conditions, water conditions, man-made structures, plankton, algae, invertebrates, fishes, birds, mammals, hazardous aquatic animals, and predators. 3. Understand marine pollution and identify the common types. 4. Know how to preserve the underwater environment. 5. Understand the negative effects divers can have on the environment. PHYSICAL ASPECTS - WATER MOVEMENT WAVES Waves are a series of undulating energy forms that move through water while the water remains in the same place. Waves are generally propagated on the water’s surface by wind and move in the same direction as the wind. They are secondarily caused by geological disturbances and by the gravitational influences of the sun and moon. Waves are measured in terms of their height, length, and period (figure 2-1). The height of a wave is the vertical distance from its crest (highest point) to its trough (lowest point), and is usually measured in feet or meters. The wavelength is the horizontal distance between successive crests (or troughs), and the period is the time required for two successive crests to pass a given point. The volume of water transported by a passing wave is negligible and can be disregarded for all practical purposes unless the wave breaks. The water particles within a wave move in an orbital motion as the wave form moves forward, returning to nearly their original position as the wave passes (figure 2-2). This means that objects do not relocate horizontally underwater due to wave action, although they can move to and fro, a phenomenon known as “surge.” Objects are transported by wind at the surface or by currents underwater. The surface particles move in a circular orbit which equals the wave height. Beneath the surface, the orbits become smaller and smaller, finally diminishing to nothing at a depth equal to approximately one-half the distance between waves. If waves have a wavelength of 15 m (50 ft), the influence of those waves will be greatly diminished at a depth of 8 m (25 ft) or more. Still-Water Level Wavelength Direction of Wave Movement Wave Height Trough Crest Surge Limit Depth FIGURE 2-1. WAVE TERMINOLOGY Direction of Wave Movement Orb FIGURE 2-2. WAVE ORBITALS AND SURGE
20047TC
To see the actual publication please follow the link above