Environmental Engineering Reference
In-Depth Information
steepening as it is opposed by river flow. Several million people living around its shores
were relieved that calm, anticyclonic conditions prevailed during the twentieth century's
highest spring tide in September 1993; a
storm surge
reinforced by cyclonic low
pressure and strong winds could have been catastrophic.
High tides occur simultaneously at a number of places, linked by
co
-
tidal lines
as they
are drawn across the ocean. The ocean surface tilts as it ebbs and flows, moving away
from and towards land, and is also tilted by the Coriolis force. As a result, the water
surface in enclosed oceans or seas oscillates from side to side around
amphidromic
points
with zero or very low tidal range (Figure 11.12). Coastline configuration also
influences
Figure 11.12
Co-tidal lines, amphidromic points and tidal
range around the British coast.
tidal range. Open coasts capable of reflecting tides with little complication, or enclosed
seas like the Mediterranean with limited scope for tide generation, experience
microtidal
ranges less than 2 m in amplitude. More indented coastlines and wider continental
shelves, enhancing wave reflection and retardation, raise tides to
mesotidal
or
macrotidal
ranges of 2-6 m and over 6 m respectively.
WAVES
Waves are the smallest mass disturbances, dependent on the wind and therefore transient
and irregular in strength and direction, except in the sense that predominant wind
directions excite a similar response in wave direction. It is important to note that waves
transmit energy but very little mass - i.e. a wave is an onward transmission of energy
from one water particle to the next in which the wave form is created by the rotational
rise and fall of each particle in turn (Figure 11.13). This is demonstrated by the rise and
