Wave Construction McLaughlin

Published on November 16th, 2014 | by Ben Nielsen

Photo by McLaughlin |  13

The Two Types of River Waves: Which One Are You Surfing On?

A professional kayaker once told me that holes are a “dime a dozen” but waves are something special. I thought this was a great way to put it and probably the reason we surfers (and kayakers) search far and wide to score a river wave. How many times have you driven around a river bend expecting to see the next undiscovered wave only to see whitewater chaos, but nothing ride-able? So why is this? As a wave designer I spend my days answering and agonising over this precise question.

There are two types of river surf waves — Hydraulic Jumps and Sheet Flows. A Hydraulic Jump Wave forms when fast moving water slows down because of the water downstream, called “tailwater”. There are many examples of Hydraulic Jump Waves:

By contrast, a Sheet Flow Wave forms when fast moving water flows over a bottom contour that shapes the wave but is not affected by the tailwater. The best example of this is the Cunovo Wave in Slovakia. Note in the video how much the pool downstream is below the wave – not impacting the wave at all. In general, a hydraulic jump wave is the only type that forms naturally in rivers. I suppose a sheet flow wave could form in a river, but I personally have never seen or ridden one.

Hydraulic Jump Wave or Sheet Flow Wave?

I have been asked which is better a Hydraulic Jump Wave or Sheet Flow Wave? That is a tough question and probably more of a personal preference. For me, I can’t tell the difference when I’m surfing as long as the sheet flow wave is deep enough to ride full profile and stiff fins. Although shallow sheet flow waves like the FlowRider™ are super fun, I prefer the feeling of driving through turns as only fins allow. Hydraulic Jump and Sheet Flow Waves are formed by two fundamental elements — hydraulic drop and flow.

Flow: It’s obvious but without water there are no river waves. Also without enough water it’s not deep enough to surf. My experience is that a minimum flow for a surf wave is about 15 cubic feet per second (cfs) per foot of width of wave (1 cubic meter per second per meter) but this is very dependent on various hydraulic conditions.

Hydraulic Drop: This is energy available to create the wave. More drop equals bigger waves right? Not exactly, there are practical limits. In general, 2 to 4 feet of drop is ample to create good waves.

Neil Egsgard with the Surf Anywhere Project wrote a great article for Riverbreak on the basic elements needed to create river waves. Check it out for more info.

The Four Types of Hydraulic Wave Formations

My expertise is designing Hydraulic Jump Waves. That’s the kind of wave most commonly surfed. Hydraulic jumps are affected by many factors, none more than tailwater, the depth of water in the downstream pool. Depending on tailwater there are typically four unique wave/hole formations:

#1: Pour Over (Lowest Tailwater) — Can be hazardous to river users due to strong upstream currents.

#2: B Jump (Low Tailwater) — A hole formation (breaking wave) that occurs just downstream of the structure.

#3: Max Wave (Perfect Tailwater) — The holy grail for river surfing.

#4: A Jump (High Tailwater) — Hole formation (breaking wave) that occur on the structure.

Video Illustrating the Various Wave Forms

Check out this video during a MWDG physical model that illustrates the various wave forms. Note how the wave form changes with tailwater. Can you find the four wave forms?

As you can see in the video, the Max Wave, what we all want to ride, is very sensitive. The height and steepness needed to surf requires a specific tailwater depth. Herein lies the crux of the wave building problem. To further complicate the matter, there are many variables besides tailwater that affect Max Wave — drop, flow, geometry of wave structure, slope of approach, downstream pool configuration, and others.

How to Design a Max Wave

There are two approaches to effectively design a Max Wave. Trial and error may work in canals and other very controlled environments but still may never yield a Max Wave suitable for surfing due to so many variables or may be cost prohibitive particularly in natural rivers.

Real-Time Adjustability – WaveShaper™ (developed by MWDG) to solve the Max Wave problem. The WaveShaper™ can be adjusted to affect the approach angle, drop, and tailwater relative to the structure – three of the biggest factors. Design is still very important even with real-time adjustability because the range that Max Wave occurs is still easily missed. In addition, the more adjustability a feature has the higher the cost so accurate design is key. The Boise River Park is a good example to illustrate how the WaveShaper™ works and it’s applicability to river surfing.

Static Features – Boulders or concrete structures. This requires the highest level of design and experience to reliably create a Max Wave. MWDG designed a static feature called the Treadmill Wave in Columbus Georgia. In general, the best static feature waves occur with higher flows than required by the WaveShaper™, which is often not available.

Getting your Wave Built

So what does all this mean to ripping your first turns? If you surf a man-made wave already, consider yourself lucky and buy the designers/builders a beer (or two) next time you see them, it’s a great accomplishment. If you want one built in your town, get in touch with an experience designer that has had success building surf waves. If you are keeping it natural, keep hunting around that next bend and hope for highwater. See you on the river.

By: Ben Nielsen, PE, LEED AP

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Ben Nielsen

is a professional licensed engineer with McLaughlin Whitewater Design Group in Denver Colorado. He was the design engineer for the Boise River Park and Chattahoochee River Restoration in Columbus Georgia. While attending Cal Poly, where he received a degree in civil engineering, he fell in love with surfing the powerful, empty lineups of Central California. With Ben’s passion for rivers and surfing combined with expertise in hydraulics and fluid dynamics he is advancing river wave design to bring land locked surfers, like him, the stoke of riding waves. Ben has presented at many U.S. and international conferences on various topics related to river recreation design. Most recently, he presented design strategies for integrated recreation and fish passage projects at the 2013 International Fish Passage Conference and design of surf waves in natural river systems at the 2014 Forum Flusswellen in Munich.

  • Jacob Kelly

    Awesome article Ben!!!
    It won’t be long before more of these waves will be built around the world!! The future of river surfing is hunting for naturally formed waves in combination with surfing man made features! The more waves that get built the more research goes towards getting better at achieving Max Waves. Even Ryan, the wave tech at the Boise River Park, has put a lot of time and experimentation into forming better and better waves. The more waves we can build in different locations, the more experience the world will gain for shaping perfect waves : )

    Stoked for things to come! So happy passionate and knowledgable people like Ben are out there giving their life to wave building!

    To health & highwater!

    • http://riverbreak.com/ Riverbreak Magazine

      Yes, guys like Ben and Ryan are at the forefront of wave construction! Jacob, try to think of what comes after Max Waves? I mean, can you imagine that we build Barreling Waves in rivers. Most of the waves that barrel in the river are natural river waves, but one day we will be able to actually build these monsters!

      • Jacob Kelly

        1. Munich’s Eisbach is where the bar is set for world class.

        2. A river barrel is the ultimate test of river wave construction, if we can build a barrel the traditional surf industry will certainly start to take notice.

        3. The real future as I see it it dynamic river waves. Similar to the hydraulic wave in Boise but something that changes as you ride it. It would be more similar to riding a line in a skate park or down a mountain. We won’t just match ocean surfing and the other sports that have influenced river surfing but surpass them creating something completely new. This all rests on the shoulders of talented wave engineers and designers!!! (no pressure Ben)

        • Ben Nielsen

          I love this insight Jacob! I totally agree. First goal is consistently build more quality river waves that give people all over the world an opportunity to surf river waves…..that would be a beautiful thing. We have some innovative wave designs in the works. Now i need to find a locale to build it!!

          • Jacob Kelly

            I have a great little spot for you on the Kananaskis river, up here in Alberta!!! Drop by any time!!

  • Alex hall

    Please Côme to Montréal, se have two types of sheet flow wave naturally occuring in the st-lawrence river that you could surf or kayak and also study. They have Nice mitts and bouncers because of the features around them. If you have ever heard of big John, or habitat 67, you will understand that the quantity of water coming down the river makes the waves but also the edies around those waves make the sweet spots on them. There is also another big one that is called Mavericks, that one is a one shot deal tough and is only accessible after a juge effort from the Eddy of big John or by jet boat. If you come around mtl next Sumner please email and i’ll ne more than happy to show you the spots. Hall.alex@hotmail.com

    • http://riverbreak.com/ Riverbreak Magazine

      Hey Alex, thanks heaps for your comment … H67 and Mavericks are two absolutely sick spots! We’d be more than happy to get in touch with you when we make it to Montreal. Hopefully next summer! Would love to meet up with you, have a surf and chat with you dude!! ALOHA!

    • Ben Nielsen

      Alex thanks for the invite. I have heard great things about the waves in Montreal! Surfing up there is on my wish list. I will hit you up when I come up.

  • http://www.testboot.de Gert Spilker

    10years ago we built an artificial wave in Muttershotz / France just by narrowing the downstream river tongue from the sides. Waves are oszillations, and by moving up/down-stream 1-3feet the knot point (= first wave = initial wave) we could adjust the second wave in a way that it hits the flatwater building a wave or a hole.

    The wave is perfect for surfing and resembled to the OLD Rabioux Wave / Durance / France (before year 2002)

    • Ben Nielsen

      Sounds like a simply good design. Do you have any video of your wave? I’d love to surf it sometime!!

    • http://riverbreak.com/ Riverbreak Magazine

      This is sick — would be neat to see this idea implemented in other rivers too!

    • Alex Mauer

      I would also love to see some video of the wave! Sounds cool!!!

  • Bill Kirby

    I ran across a journal article a number of years ago (that I can’t now lay my hands on) that concluded the critical parameter for the difference between an aerated hydraulic jump and an undular hydraulic jump, i.e. a surfing wave, was the relationship between t he depth of the tailwater and the height of the obstruction that caused the acceleration of the flow. If the tailwater elevation was higher the elevation of the obstruction, a wave was formed. If the tailwater was below the obstruction a hydraulic was formed. Does this agree with your research and experience?

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