running small dams

Keep swimming when you should be rafting? Share or beg for tips and technique .
Post Reply
blisterfree

running small dams

Post by blisterfree » Wed Apr 29, 2009 12:34 pm

A local river here in the NE, one of the old urban/industrial rivers, offers some convenient and interesting paddling opportunities, but also features a fair number of dams. Portaging usually isn't very problematic with an Alpacka, and some of the dams are small enough to be easily run when the river is sufficiently high. On the other hand, some of them look more like this:

http://picasaweb.google.com/blisterfree ... 1340537474

That's a vertical drop of about 4-5 feet, typically with adequate river depth both above and below and a modest current (it's a little low as seen here). Assuming I steer my Denali Llama bow-downriver over the drop, what happens next? Any tips in terms of approach speed, body position, and paddle technique? I assume some aggressive paddling may be required to float free of the hole at the base of the falls. But I can't quite envision how the boat will behave en route over the drop.

To wit, is running a dam such as this no big deal or more trouble than its worth?

Arturgreen
Posts: 46
Joined: Wed May 07, 2008 10:52 pm

Re: running small dams

Post by Arturgreen » Thu Apr 30, 2009 12:12 am

Try it and let us know? :)


I've often wondered the same thing...

blisterfree

Re: running small dams

Post by blisterfree » Thu Apr 30, 2009 7:38 am

Not likely!

My main concern is that the bow gets caught in the hole and I end up being thrown out forward while still on the vertical. That, or I hit the back of my head on the dam somehow.

On smaller (1-2 ft) dams that I've run the raft breaches the drop, bow and stern, so there isn't any "hang time." And the current naturally seems to pull the raft through the hole without much input from me. Here (on a 4-5 ft dam) there would seem to be a greater chance of losing beneficial downstream momentum. Or it could all be over with, no worries, before I've had a chance to scream for mommy.

That's what you experts are here for, right? To end my wanton speculation.

Shaggy
Posts: 172
Joined: Thu Aug 23, 2007 10:51 am

Re: running small dams

Post by Shaggy » Thu Apr 30, 2009 4:03 pm

Hi Blisterfree,

The runnability of a low-head dam depends on the dam, from "non-event" to "death trap" :!:

Basically, if the flow over doesn't create a hyrdraulic / recirculation of any significance, then - as long as you don't bonk your head on something - you're just doing a little drop, and at worst will take a swim. However, as the flow gets larger and more powerful, it creates a powerful recirculation zone from which escape is almost impossible, due to the fact that it stretches from bank-to-bank.

I don't feel comfortable assessing from a photo, and because I don't personally have a lot of experience with these dams. The really important question is "if you swam, could you easily swim out of the there?" and "is there a junked '57 chevy under there?" :o What's really great is to go out with someone who has whitewater rescue time or lots of river experience, and get their read on some of these, so you start really knowing what to look for. Sorry I can't be more definitive for you...
All posts are personal opinions only.

"Boldness has a genius, power, and magic." -Goethe

blisterfree

Re: running small dams

Post by blisterfree » Fri May 01, 2009 8:42 am

Shaggy, thanks! In hindsight I couldn't have hoped for a more sensible answer.

I will have to go dip my toes beneath the dam and see what I find, junked 57 Chevys or otherwise. Very good point about the bank-to-bank hydraulics that are peculiar to dams.

Proceeding with an abundance of caution...

DaveChenault
Posts: 111
Joined: Wed Jul 23, 2008 6:04 pm
Location: Kalispell, MT
Contact:

Re: running small dams

Post by DaveChenault » Fri May 01, 2009 10:43 am

Back in high school in Ohio the rivers we kayaked had quite a few dams like that. Some were trivial, some undercut such that runable flows produced certain enders if you didn't punch them with lots of speed. I presume Alpacks don't punch water like that, and are very prone to bandersnatching.

I'd stay away, those little dams can be nasty.

turk

Re: running small dams

Post by turk » Tue May 19, 2009 5:07 pm

One of the things not being mentioned here is exactly what the dangers with
low head dams are.

For ANYONE not familiar with reading whitewater and understanding the forces
and physics involved with moving water, the next sentence could very well save
your life: LOW HEAD DAMS KILL MORE PADDLERS THAN ANY OTHER RIVER
FEATURES COMBINED.

why? well its pretty simple. To the average joe, they look pretty harmless. A
quick little drop, and you paddle on down an otherwise pretty tame section of river.
A lot of people actually go out and pick a low head dam to run as a precursor to
actual whitewater experience.

What about them, makes them so dangerous?

Okay here we go:
Most people can figure out the basic danger of a natural hyraulic. "Its below the
drop that is going to suck me backwards and pull me towards the actual water curtain.
" Think of low head dams, as a treadmill on water. If it is moving faster and more
powerfully than you can paddle, you are in real trouble. Oh ya, and nature's treadmill
doesn't get tired. Plenty of paddlers make it over the drop with no problems,
only to get stuck in the hydraulic paddling as hard as they can, going nowhere, until
the've burned up all the juice left in their arms and completely spent themselves.
Eventually you will give up .... then you get pulled back. When you hit the curtain,
water fills and usually swamps the boat. This is when you are upside down, rotating end
over end, all the while being pushed backwards into the curtain of falling water or worse ,down
and backwards. How many front or back flips can you do underwater before you lose all
sense of direction. Thats a game we played in the pool as kids. Personally Im totally
disoriented after 3 or 4 rotations.

In a natural hydraulic you have 3 ways out - overpower it physically by paddling or swimming,
move parallel to the hydraulic until it gets weaker and you can break free, and / or luck or
some irregularity of flow it spits you out when its good and ready.

With a low head damn there are 3 big killers that naturally formed hydraulics don't have.
The dam is almost always a uniform flat concrete or steel retaining wall that spans the
entire river. This means that the hydraulic formed also spans the entire river and
exerts an equal force across the entire river. So if you can't overpower it physically,
moving parallel towards either shore isn't going to be any easier, if you can move at
all. Man-made river features are too perfect. The second deadly feature is that
the wall of the dam is usually a perfectly flat and vertical or near vertical surface.
No major irregularities across the face of the concrete or steel damn. If your body is
thrown back and against the wall, you are stuck worse than in a naturally occuring water
fall that usually has enough irregular surfaces that you can claw, push off of, and otherwise
get yourself free and moving parallel and out of the hydraulic. (except for caves, but thats
another discussion entirely). Low head dams are just smooth walled death traps with
nothing to grab, and nowhere to move to even if there was.

Lastly, low head dams are almost always in areas of some built up civilization and that
means "Townies"... "No city or urban development has ever done any good to an
innocent river nearby". Low head dams with their uniform in-escapable river wide
hydraulic are like giant rotating garbage mounds. Every piece of garbage, shopping
cart, spare tire, plastic bag, beer can and snarled knot of fishling line from miles and
miles upstream, eventually ends up in the churning, unforgiving hydraulic at the base
of a low head dam. just .. yummy. Just one more added element to make a life and
death situation that much more interesting.

And the last element of danger.... misreading the danger level. Because the hydraulic
is so uniformly perfect, even accomplished class V paddlers can miss-read the sheer
strength of the currents they produce. Generally speaking and this is VERY general .
... look at the width of the band of water that is flowing back towards the curtain
against the current. The wider the band, the more powerful the rotational force of
the hydraulic. If the band is wider than your boat is long ... you are tossing the dice
with your life. Irregular flows or breaks in the perfect band usually means large foreign
objects that have come down river and been pinned in the hydraulic.

That is not to say that all low head dams are waiting to catch and kill you. Its extremely
dependent the actual flow of water going over the dam. Most river gauges are located
right on low head dams because its so easy to take accurate readings. If you're not into
metric yet - (get with the rest of the world America :D ) I will provide a translation here
from Canadian/restoftheworldese to Imperial here: A cubic foot of water weighs 62.5lbs.
A 5ft x 30" standard steel bathtub holds almost exactly a cubic foot of water. River gauges
often have two scales on them. One of which is cubic feet per second. There are all kinds
of 'rules of thumb' to aproximate flows, but actual river gauges never lie and are
always precise, instead of 'close' ;) The more cubic feet of water per second spilling over
the dam, the more weight and total force driving the hydraulic at the bottom. A measly little
10cubic foot flow is equal to 625lbs of force, pushing your body in a direction opposite to where
you want to go.

SO ya .... thats whats dangerous about low head dams. They look like nothing... and thats how
they get so many people. There is a reason you don't see any world class kayakers or videos on
youtube of pro paddlers messing around in low head dams. Experienced people know to avoid them.
Inexperienced people continue to take on low head dams ever year looking for a quick thrill, and
sometimes paying the ultimate price.

Sorry that was so winded. I just think its important that anyone thinking about running low head
dams, KNOW beforehand how dangerous they are.






Personally, I would rather run a C-5 concrete fishladder in full 'rag-doll' position than take a gamble and
bail in a high volume low head dam.

RomanDial
Posts: 428
Joined: Mon Oct 01, 2007 11:13 am

Re: running small dams

Post by RomanDial » Tue May 19, 2009 9:34 pm

Awesome answer Mr. Turk.

Shaggy
Posts: 172
Joined: Thu Aug 23, 2007 10:51 am

Re: running small dams

Post by Shaggy » Wed May 20, 2009 10:09 am

Well said indeed, Turk.
All posts are personal opinions only.

"Boldness has a genius, power, and magic." -Goethe

Arturgreen
Posts: 46
Joined: Wed May 07, 2008 10:52 pm

Re: running small dams

Post by Arturgreen » Tue Jun 02, 2009 12:19 am

I wanted to thank both the original poster and turk for this discussion. I was rafting a large river here in Belgium this last weekend and I came to a ~2-meter concrete dam similar to the ones described here. I studied it for awhile, but thinking of this discussion I decided to just portage it.

However, I'm pretty sure I might have given it a shot out of ignorance otherwise. Maybe it would have been fine. Maybe not.

Shaggy
Posts: 172
Joined: Thu Aug 23, 2007 10:51 am

Re: running small dams

Post by Shaggy » Tue Jun 02, 2009 6:42 am

I think a key point is that if there's any uncertainty, it's not worth taking the chance. Someone with sufficient expertise & training here might now feel that uncertainty (and I'm not that person :) ), but for the rest of us, the voice of uncertainty is a great guide.
All posts are personal opinions only.

"Boldness has a genius, power, and magic." -Goethe

damt
Posts: 16
Joined: Sat Jun 20, 2009 3:08 am

Re: running small dams

Post by damt » Sat Jun 20, 2009 3:12 am

Thanks for the instructive post Turk.

arthurgreen, just out of curiosity, where was that dam ? I live in Belgium too (close to Liège/Luik), but I haven't done much paddling here though.

Post Reply