Wave Construction River Drop and Flow

Published on July 19th, 2013 | by Neil Egsgard

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Surf Anywhere: Drop & Flow

Surf waves can be built anywhere you have enough fast water.  Figuring out where you have enough drop and flow is the first step to building a wave.  The Surf Anywhere Project and Riverbreak are sharing this information to help you build waves everywhere.

Drop Provides Wave Speed

If you have a 1 metre drop in a river with a 30 cms flow you can build one of the best waves in the world.

The drop in elevation from upstream of a river wave to downstream is the wave’s energy source.  The larger the drop the faster the water.  The faster the water the more energy available for the wave.  The Eisbach has a drop of about 1.1m or 3’7” from the channel bottom above the drop to the channel bottom after the drop.  If you have a 1 metre drop you can build one of the best waves in the world provided you have enough flow. The figure below depicts how these components relate to each other and how they work together so that a river wave forms.

Flow Provides Wave Thickness

The flow is the volume of water per second going through a river (depth X width X velocity).  The more flow you have the bigger and thicker the wave can be. The average flow rate of the river above the wave, on the wave and below the wave is always the same.  If you increase the velocity than the width and/or velocity or must decrease.  The Eisbach has a flow of about 30 cubic metres per second (cms) or 1,060 cubic feet per second (cfs).

How Water Changes With Drop and Flow

 Drop     Water Speed      Water Depth

Flow    Water Depth

River Width     Water Depth

Making Waves With Drop and Flow

High Flow + Wide + Big Drop = Wave

If the channel is too narrow then the water will be too deep for a wave.  If the drop is too small the water just fills in the wave.

Small Flow + Narrow + Small Drop = Wave

If the channel is too wide then the water will be too shallow for a wave.  If the drop is too big the water will be too fast and therefore too shallow for a wave.

Amwelle: Low flow, narrow, small drop and a fun wave

 

Eisbach: Higher flow, wide, larger drop and a good wave

Surf Anywhere Project

This is the first of a number of articles on building river waves driven by the Surf Anywhere Project.  The other articles will cover different fundamentals of river wave building making it easier for surf waves to be built everywhere.  If you have any questions about building waves near you or information to share, please contact me – negs (at) riversurfing.ca

This article was written by Neil Egsgard, Surf Anywhere Project Lead 
Surf Anywhere Project — SurfAnywhere.ca
Alberta River Surfing Association — RiverSurfing.ca/forum

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Neil Egsgard

Neil Egsgard is the president of the Alberta River Surfing Association (ARSA) and leader of the Surf Anywhere Project -- a project to share wave building details and knowledge so waves can be built everywhere. He loves river surfing, believes surfing can be anywhere, built RiverSurfing.ca in 2009 to share and record the sport and since 2005 has surfed river waves from big to small all over Western Canada and the northwest United States.



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