Geology Reference
In-Depth Information
stream to the ocean, the sediments are deposited in the dam-created lake. And, of
course, this lake has been created where there was not a lake before, flooding habitats
and displacing creatures, including (in many cases) humans.
Shaping Waterways
Damming is only one way humans act as geologic agents to flowing water. Humans also
straighten and deepen river channels to provide access to inland cities for the shipping
and tourism industries.
Many river channels are not naturally deep enough to allow the passage of large freight-
er ships that transport goods around the world. The solution, of course, is to dig the
river channel deeper by removing sediments. This process of
dredging
acts as a short-
term, massive erosional force — taking sediments from the river channel and transport-
ing them elsewhere.
Similarly, a river's natural path may be changed by the construction of a concrete chan-
nel to help direct the water where humans want it to go, rather than where the natural
shape of the landscape sends it. The Seine River in Paris is shaped in this way —
straightened into a smooth curve through the center of the city and guaranteed not to
change course.
Nourishing Beaches
Coastal beaches depend on rivers to carry sediments from the continent to the sea. As
the river washes the sediments into the ocean, the waves carry sand up and onto the
nearby beaches. But this natural geologic process of beach building is halted by
changes upstream.
When humans change the course or sediment load of a river, the sediment that normally
would have been brought downstream to the ocean and deposited along beaches is no
longer available. To fix this problem, humans add sand to the coast in what is called
beach nourishment.
To build up beaches, sediments are brought in from somewhere else
and deposited along the beachfront. However, these added sediments may not be the
right size to withstand the erosional forces of waves or to support the natural ecosys-
tem.
