Measuring River Waves

Whilst the perfect ocean wave can only be given to us surfers as a gift from mother earth (or sea), man is able to construct stationary waves in rivers or in special basins using water pumps or other kinds of advanced hydrotechnology. But finding the perfect spot for a constructed river wave is not that easy. Again, specialized technology helps us deciding exactly where in a river bed the potential for constructing a surfable wave is at its highest.

This spring a bunch of interested people joined together to measure the bed of the river Mur in Graz, Austria. Surfers, kayakers and wave engineers teamed up with city officials to think about how to manoeuver a small, unmanned and unmotorized scientific plastic trimaran sideways across a river.

The first attempt was to simply attach a rope (approximately 14 meters long) to the boat and guide it from one side of the river to the other while walking on a bridge. But according to the plan developed by Michael Strömer, a wave engineer from Graz, we needed more of these “lines” of measurement. But how do you move a floating device straight across a 40 meter river bed?

After exchanging some thoughts and ideas we finally sticked to this one: First different lengths of ropes (used for rock climbing) were tied together and laid down on the bridge. Then one person held the end of the rope standing on the bridge while the first team went down to the shore with the other end of the rope, attaching it to a tree trunk. As soon as that end of the rope was fixed, the person on the bridge attached a second auxiliary rope to the bridge to hold the middle of the (main) rope firmly attached to the bridge.

The question was, how do you move the boat from one side to the other?

Then the second team moved down to the shore at the other side with the untied end of the main rope. Because it would otherwise consume too much of the rope the second team always pulled the rope slightly down to the shore while the person in the middle of the bridge gently loosened the auxiliary rope until running out of rope. As a (calculated) result the main rope fell into the river and was quickly pulled out with several moves by the second team which fixed the tightened rope to another tree.

Now we had constructed a long rope across the river where the boat could be attached via a return pulley, but how do you move the boat from one side to the other? We needed another (steering) rope! I will spare the details on how we got this one across the river…

Finally to move the boat across the river each of the teams standing on the river shores pulled the steering rope. The desired result was a (surprisingly easy to understand) graphical profile showing a) the depth profile of the river bed and b) the water flow rate at any given point.

Three spots have been measured using this method: The Radetzky spot, the Hauptbrücke spot and the (soon-to-come) “Edegger” spot near the Murinsel in Graz. Totally exhausted I went home only to realize I’d got my first sunburn this year. For what it’s worth.

Measuring river waves photo gallery

More about: Austria Europe Graz How-to Mur Wave Construction

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Börny Börny was forced to surf the river Mur in Graz / Austria for the first time in 2010 (by PhilK) during the time he made a movie called 'murtreiben' about the local riversurfing scene (sounds very similar to PhilK's story). Since then he decided to surf rivers instead of making movies. And now there is Riverbreak!