Surf's up(stream)

Don K, Sioux City, IA — Wed, 20 Aug 2008 16:35:51 GMT

My take is that it's some sort of a spillway and they're surfing the bottom. Pretty cool.

Surf's up(stream)

Alex, Lenexa, KS — Wed, 20 Aug 2008 19:11:22 GMT

Will,
It is probably the outflow from a dam, they usually have a concrete slough that comes out the bottom of the dam for outflow. Usually at the end of the concrete slough there is that wave effect as the water drops into the soil and then turns back upwards.

Surf's up(stream)

Freeway — Wed, 20 Aug 2008 19:55:12 GMT

we surf behind ski/wakeboard boats. get a big enouph wake to curl the wave and you can surf about 4 feet behind the boat with no rope.

Surf's up(stream)

Thu, 21 Aug 2008 01:24:55 GMT

yes, you are right, the water pattern matches the underlying rock pattern.

though the water pattern depends partly on the river's water level, which is highest when snows melt.

and there are more rocks downstream to hit too.

and not forgetting that many rivers, including the Delaware, Passaic, and Miami, long ago had many more natural rock barriers and waterfalls, and some rock barriers made by indians as wiers to catch fish, mostly long ago removed.

http://www.scenicbuckscounty.com/MorrisvilleTides/FallsOfTheDelaware.html

http://www.lutins.org/weir/

Surf's up(stream)

Evan, southern Oregon — Thu, 21 Aug 2008 09:46:06 GMT

The structure that is causing the wave is upriver from them. THe water is falling down over this item, and this is the first wave in the ripple pattern that follows downstream. This could be a rock, but I'm guessing it's more likely some sort of man-made piece that disrupts the water flow. I'm guessing that the water is fairly deep where they're falling.

Surf's up(stream)

Larry — Thu, 21 Aug 2008 13:23:31 GMT

It's probally a channel, or a trench, in the river.

Surf's up(stream)

anon — Thu, 21 Aug 2008 17:58:05 GMT

Nope, not hitting anything. The water is piling up just after a drop off, creating the larger wave. The smaller white water wave behind it is just what is piling up after spilling over the large wave. Looks like water coming off of a small spill way.

Surf's up(stream)

Brian, Philadelphia, PA — Thu, 21 Aug 2008 18:36:05 GMT

Will, this looks like one of those "stationary" surf machines they have at waterparks and on cruise ships. I wouldn't be surprised to see a small dam or spillway to teh right, just out of frame.

Surf's up(stream)

Alderberry Q. Thistlepuck — Thu, 21 Aug 2008 21:30:16 GMT

Waves like that can be caused by several things, rocks being one of them. That’s called an obstruction; other things that can cause waves are, constriction, Laminar flows and change in elevation(of the river bottom). And by all kinds of combinations of these.

The one in the video appears to be caused by a change in elevation and some Laminar flows.

I’ve been a whitewater river guide for almost 30 years and have seen a lot of attempts to surf waves, some very successful and some not.

Surf's up(stream)

JB Redmond, WA — Thu, 21 Aug 2008 22:31:58 GMT

No, they'll move downstream of the rocks.

Ocean waves move while the water stays still (fairly, until the wave breaks). River water moves while the waves stay still. Relative speed of the board vs. the water is similar, but the physics of balance and motion take a bit of learning, when switching from one to the other.

Surf's up(stream)

WFC Tulsa, OK — Fri, 22 Aug 2008 19:12:54 GMT

Skilled kayakers and canoist have been doing this for years. Just a delicate balance between gravity, drag, and water flow (ala JB Redmond)It is perplexing to watch though.

Surf's up(stream)

Mike, Chicago, IL — Mon, 25 Aug 2008 20:08:02 GMT

This spot is in the English Gardens in Munich Germany. The Eisbach River was diverted to flow into the park and this was the happy result. The river flows out of a tunnel under the city. Surfers must be careful, as the rock is only about 40cm below the surface.