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Like other water bodies, creeks form in low-lying areas, but unlike
lakes, creeks form where there are continuous narrow stretches of
low areas called valleys.
Most valleys in the Hamilton area were begun by the movement of
glaciers. Glaciers scrape off surface layers of soil and rock as
they grow and advance across an area. When they retreat, they leave
behind low-lying areas where these materials have been removed.
Water drains, or 'runs off', to these areas under the force of gravity
and pools. Where there are longer stretches of low land, water flows
along, again under the force of gravity, until it is able to escape
to even lower land often through a gap in the landscape.
Areas
through which water can flow become eroded over time by that water,
creating deeper and deeper channels. If the soil and rock is easily
eroded this can occur very quickly. If the underlying material is
very hard, it takes longer but still happens. The result is a river
valley. Sometimes valleys are called ravines although ravines are
usually either very shallow creek valleys or very short cuts in
a slope not long, winding creek paths.
Note
the red banks of the Red Hill Creek.
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Because
creeks have eroded through layers of soil and rock, they expose
layers that are not visible elsewhere. Visit the creek nearest to
you and, if it is safe to do so, look closely to see what the material
in the bottom is like. It may be fine sand, silt or sticky clay.
Some local creeks bottoms are quite flat and hard where the surfaces
of sedimentary rock layers are exposed.
Creeks are as subject to climatic effects as the land around them,
but not in the same way.
When
there is a great deal of rain, creeks swell and run more quickly.
If the rain is warm the creek temperature may temporarily rise but
creeks rarely become permanently warm like ponds can.
In
times of low rainfall, some smaller creeks can dry up completely
becoming dry creek beds for short periods of time. Some creeks are
dry in the winter, especially if there has been little snow and
few thaws to melt the snow which does exist. Dry creeks can also
be the result of over-extraction of water for agricultural and greenhouse
irrigation. Spencer Creek in particular is under this kind of pressure.
Creeks that dry up from time to time are called 'ephemeral'.
| 'ephemeral'
means lasting a short time |
These
ephemeral creeks are still important habitat areas but not over
as long a season as creeks that flow more often.
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