I compose these brief notes while the unfortunateness
of Florence takes aim at the East Coast. I offer it in the hopes that we may
have it at the fingertips of our minds for as Seneca reminds us “What has befallen one man may happen to all”
or as the Boy Scouts would say “Be Prepared.”
The
following ideas are gleaned from naturalist studies in river-dynamics, the
frontier scout tradition, and an American Indian tactic or two. Keep in mind
when we discuss river-fluid mechanics these same mechanics will hold for
“concrete rivers,” that is, streets turned to river by flood.
Rivers basically have
two broad aspects to their composition Upland & Lowland. In the Upland
portion the land is steeper and we find more energetic water. In the Lowland phase,
it flattens out and at times we may see only a yard drop in elevation in a ½
mile of travel. The idea to keep in mind is that the faster or more energetic
the flow the closer to the source we are, and the more care we must exercise
when entering the river.
Upland River characteristics: Speed,
energy, sometimes narrow and steep channels, and waterfalls. You can judge the
energy the upland river possesses in full flow by the size of the boulders, the
debris, the scatter of vehicles in the middle and along the banks. The larger
the debris the more energy.
Also—the sound. Upland rivers often provide
white water noise, not just as found at a waterfall, but in general as it breaks
over rocks and debris, or simply the sounds made by its rate of flow.
The Lowland River Phase is
usually broader and has longer straightaways and typically silent unless
something is plunked into it.
If we know that we must cross a river or
flooded street, it is wise to choose lowland phases where we can, move
downstream where possible, and avoid narrowing channels that will multiply the water’s
energy.
Lee-Scree as Force Indicator. Lee-scree
is the debris deposited by a river. In the wild, the rocks, boulders and logs
we find within the main channel and along its banks. In the urban river/flood
the cars, and all other detritus swept into its path. By noting the size of the
lee-scree in a river or stream we can gain an idea of how much energy the river
has when flowing at force. Large boulders, rocks, etc. tell us this river
carries a great deal of power, not the best place to interact with the river.
Lee-Scree as Flood Phase Indictor. Lee-scree
seen deposited above ground in “dry areas” at the side of a river tells us that
the flow is subsiding or that we are moving to a lowland phase. Lee-Scree still
in the flow at the side of the river tells us there is still more to come.
Water moves more quickly around the outside bend of a river or stream
than the inside. Think of street corners and curving streets
as correlates for river-bends. This info is useful for both reading scree and
ford attempts—don’t look to the flow of the inside bend to judge a crossing,
look to the outside bend. The inside bend water flow may look smooth and
fordable, but a look to the outside bend will tell us what we may expect to
find when we’re already a bit exhausted from fording two-thirds of a supposedly
“calm” river.
This is also useful information for those
using canoes, kayaks, etc.—in allowing current to ease workload—aim for outside
bends when going downstream, inside bends when moving upstream.
The flow is fastest in the center of the river. This is all about friction. Sailors, kayakers, seaman of all stripes
know that if you want to pile on speed look for the center of the channel or “stream”
in areas of open water. The center is often positioned over the lowest point, geographically
the Thalweg, and the reduced friction
center-stream makes for faster flow.
With the preceding in mind, when fording,
expect increased force and deeper water as you near the center.
When wading a moving river—face upstream. If you fall you want to fall towards upstream with the strength of
your legs facing downstream to dig in and stop being swept away, or at the very
least allowing your legs to be what comes into contact with debris and
obstacles rather than your head.
As the speed of water goes up by a factor of 2, the size of the object
that can be carried away goes up by a factor of 64. Keep this foremost in your mind, it is not so much the depth of the
flow that is the danger, but speed of flow.
Four inches of moving water can sweep a car away. We are not nearly as heavy or stable as an automobile.
Again, it is speed or rate of flow that is
often the danger and not depth. Many fall prey to the illusion that is safe to
cross ankle-deep water. If it is a lowland phase, go right ahead, if it has high flow---find a lowland
phase.
I’ll offer one more tip, this one from an
American Indian tradition. When the decision has been made to wade a river and
there are few exposed dry rocks to cross over on, face upriver and place your feet-toes upriver/heels
downriver—against the upriver side of rocks as opposed to on top of the rocks.
The force of the water will “stick” your feet to the rocks as opposed to being
swept off the top of them. If more stability is required use a stick in the
hands to post upriver for balance, or if no stick is handy, lean forward and
place the hands on the upriver side of stones and scuttle sideways to ford.
May this information need never be used, but, judging
from the size of the storm…
Better prepared is better prepared.
To those in the path of Florence, and Florences
yet to be, may it serve well.
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