Rapids have strong eddies and currents and moderately sized waves. Good boat control is required, but major hazards are easily avoidable. Rapids are powerful and turbulent with large, unavoidable waves and holes or constricted passages. Safe navigation requires precise boat handling.
Rapids often require "must-make" moves to avoid dangerous hazards. Rapids are long, obstructed, and violent with exposure to substantial risk. They require expert-level boat handling to navigate unavoidable waves and holes or steep, narrow chutes.
Class VI runs are un-runnable to to all but the most advanced paddlers, and are the frontier of whitewater difficulty. Rapids must be run without error, and rescue may be impossible. The river is a very dynamic setting, with many factors coming into play.
The grading of rapids is very subjective and can vary from region to region. If you are unsure remember to start small. There are hundreds upon hundreds of side canyons and drainages that bring water into the Colorado River.
With a few exceptions, many of these side canyons are dry year-round, except during rainstorms. During these heavy rains extreme flash floods can carry massive amounts of debris, rocks, and sometimes large boulders down into the Colorado River. All this debris can dam up the canyon and force the water to slow down and pool at the top of the rapid.
As the water leaves the pool it speeds up through the boulder-choked areas. Although changes are still occur year after year, most of the rapids and riffles we know today were formed in times long past. So 'white-water', which is when the water makes foam, as in the picture above, does not necessarily tell of rapids, they just tell of very fast-moving water.
Rapids are, however, common places of white water. When you get rocks with many layers, and these rocks stand up in the river bed, the weaker rocks will get worn away faster than the stronger ones. So some bands will stand up a little higher in the river bed. Generally, the guide will place the raft in the current of the tongue , a V shaped section of smooth water that indicates the deepest part of the channel through the obstruction.
Suddenly, the raft will plunge over this smooth tongue at the lip of the rapid, until it hits the first of a series of waves that the V shaped tongue of smooth fast current will invariably slam into. The largest rapids in Grand Canyon are known for having huge waves. Even some of the smaller rapids have some nice-sized waves. However, few Grand Canyon rapids are technical. Technical rapids require making one or more moves. In addition, they may require a change in direction when navigating a rapid, usually moving out of the tongue.
The more moves required to successfully navigate a rapid, the more technical and challenging the rapid. Most Grand Canyon rapids only require the raft to enter a rapid at a fairly precise location before the rapid actually begins.
Guides can then float down the tongue and into the wave train. In this scenario, the guide only needs to hit the waves straight on, with the bow of the raft perpendicular to the angle of the waves. The Grand Canyon rapids considered the most technical this varies with water levels are: Hance, Crystal the two longest rapids in the canyon , Bedrock, Deubendorf, and House Rock. At lower water levels, a few other rapids become more technical , because more rocks or sharper holes appear.
On average, it is a much higher volume than the typical whitewater river. The cubic feet per second cfs of the Colorado through Grand Canyon averages 12,,cfs in the commercial rafting season. Flows can be as low as cfs and as high as 25,cfs depending on energy needs, which dictate dam releases.
0コメント