Tony Ward-Holmes provides a history lesson on the creation of the Hawea playwave. A slightly different version was originally published in NZ Canoeing 13.1, p8-10.
Building a play-wave seems easy at first thought. You need some water for a start, and some gradient to make that water flow. To shape a wave you need a ramp or a constriction to speed up the water, preferably both. An eddy or two are needed too… a one-shot wave isn’t much use… and Bob’s your uncle, right?