The Cahaba River is the longest free-flowing river in Alabama
and is among the most scenic and biologically diverse rivers in the
United States. The Cahaba River is a major tributary of the Alabama
River and part of the larger Mobile River Basin. With headwaters
near Birmingham, AL, the Cahaba meanders to the southwest, then at
Heiberger turns southeast, and joins the Alabama River at Cahaba,
Alabama (in Dallas County).
When asked about local rivers and what they mean to them, most
people bring up recreational aspects like fishing, canoeing and
kayaking. However these rivers have much more important duties as
they begin their long journey to the ocean. The river is the
sculptor of its valley, and provides the major water-source for all
the animal and plant life in the area.
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Rivers begin rather unpretentiously. They are lazy. They follow
the force of gravity until they find the most convenient way to
flow downhill. This is governed by the topography of the area in
which they flow. In time, the river begins to modify this landscape
until it creates a valley. The average river system, if viewed from
above, looks like a many branching tree. Hundreds, perhaps
thousands, of small rivulets flow into slightly larger branches,
which in turn flow into tributaries. Eventually the water makes its
way into the main body of the river.
What does all this mean? While we patiently sit along the
river’s bank, it's easy to imagine this single entity, lazily
meandering as it begins its long journey. However, exactly the
opposite is true. The river is the product of thousands of miles of
tiny rivulets that completely dissect the surrounding terrain. As a
result, anything that takes place within the rivers watershed can
affect the quality of water carried within the river.
When the glaciers entered the scene, they adopted the
pre-existing river channels. Since glaciers are little more than a
slow moving river of ice, it seems logical that they would follow
existing pathways. As they flowed down valleys like the Bow,
Kicking Horse and Athabasca, they altered the pre-existing valleys
until they seemed very different from the valleys that had existed
prior to the ice. As the ice melted, the rivers reclaimed their
valleys and began to flow once again.
Over the past decade, we have had seen serious flooding, and
this must be carefully considered as we continue to develop the
mountains. Rivers carry a certain amount of water based on an
intricate relationship between average rainfall and runoff from the
surrounding mountains. However, the forest cover on those mountains
absorbs large amounts of that water long before it reaches the
river. By bringing in excessive developments, and removing that
large storage reservoir, we risk increased flooding as the reduced
forest cover allows ever increasing amounts of water to enter the
river channel.
Nature reacts to change very slowly. We initiate it at a rate
far too rapid for the ecosystem to respond. We must be prepared for
the unexpected changes that result from our impatience.
The Life Of A River
Water is the most powerful force on Earth. It impacts every
aspect of our life, and rivers provide its principle transport
mechanism. These rivers begin as rain and snow high up in the
mountains. As the rain hits the ground, it stirs the soil,
splashing fine sediments and dissolving minerals. Some of this
water penetrates the surface either through cracks, or by
percolating through the thin mountain soil. Some of this will later
re-emerge and enter our rivers. Some may percolate deep down into
the Earth, heat up, and resurface in one of our hot springs. This
capturing of rainfall and releasing it later is essential. If all
the rainfall in the mountains were to go directly into our rivers,
flooding would be a regular occurrence. In area’s where
overcutting of trees has occurred, we often see increased flash
flooding. For this very reason, logging is carefully
regulated.
Not all of the water seeps below the surface. As the soil
becomes saturated, water begins to flow over the surface. As it
feels the pull of gravity, it picks up speed, and at the same time,
increases in energy. It picks up fine surface sediments loosened by
the pounding raindrops, and will also carry dissolved minerals.
Gravity will take the water downhill, taking advantage of any
depression to aid its descent. In this way, the landscape begins to
be divided by small rivulets that over time will be enlarged.
Eventually, the water makes its way into a small stream and begins
its long trip to the nearest ocean.
The faster the water flows, the larger its ability to carry
sediment. As the streams flow into rivers, the water picks up
increasingly large material. Raging torrents have been known to
carry immense boulders, cars – even entire buildings. Very
little can stand in the way of a powerful river. Material carried
with the water adds to its erosive power. The material acts as an
abrasive rapidly carving through rock, deepening its channel, and
cutting through obstacles. As the river rounds a corner, water on
the outside of the corner will move much faster, eating away at the
outer bank of curves. On the inner bank, the river may deposit some
of its sediment. Over time, the river may take on a meandering
pattern.
To Claim credit for the Earthcache Please answer the
following:
1.) How fast is the water flowing right now? 2.) What is the
temperature of water today? 3.) Using the historic marker near by
what direction is Cahaba Mountain?