Building a Rapid
Passing over a riffle—bump, bump, bump, -- feels very different from plunging into a rapid’s churning whitewater. But as a basic level, a riffle and a rapid are much the same. Both are formed were a tributary flows into a main river, as the Paria river does here. Tributaries deposit sediment into the river channel. During floods this could include large boulders and rocks as well as sand and gravel. The debris clutters the river bottom and constricts the channel, forcing the river to gain speed and power. The river swirls thought or crashes over the debris-strewn riverbed, forming mild riffles or deadly crushing rapids. Paria Riffle is the first turbulence faced by boaters on their Grand Canyon river journey. Once through, over 90 named features still await them, and the rapids only get bigger. A flash flood may completely change a rapid overnight. Even on calm days, you can see the muddy Paria river depositing sediment into the clear Colorado river.
