Canyoneering Hydrology: The study of water movement and its behavior relating to the topography, which allows us to properly assess dangerous water hazards that can exist in Canyoneering.
The most common terms you will hear are swift water, whitewater or class 3 canyons. These types of canyons are located all around the world and are considerably different from dry canyons which require a separate skill set to navigate the hazards.
Swift water canyons can be extremely dangerous and as with all aspects of Canyoneering, instruction, practice and training cannot be substituted for this information.
Basics
Water behaves differently according to the volume, shape of the river bottom and types of obstructions which can then effect and produce different movements. Canyoneering Hydrology needs to be learnt to reduce the risk of injury, mishap or even death.
Three points that cover moving water especially in a Canyoneering environment are:
Powerful
Swift moving water exerts a force on any object it encounters, whether it is a rock, bridge or person in the water. This force is dependent upon the speed of the water. As the speed of the current increases, so does the power.
Continuous
Moving water will always exert a continuous force on an object or person. It never stops, unlike an ocean wave which has a cycle of breaking and receding.
Predictable
Water may sometimes look as if it is moving randomly, but to the trained person it is moving in an orderly and predictable way. Surface features can be “read” and used to predict what is happening under the water.
Characteristics
The nature of rivers in a canyon are variable and are determined by five main factors. Understanding how moving water behaves, you can use the canyon river to ascertain a level of risk management and avoid unnecessary or unacceptable levels of danger.
Topography
Topography is generally consistent over time. Increased flow, as during a flood or high rainfall season can make permanent changes to the streambed by displacing rocks and boulders, by deposition of dirt, sand or stones or by creating new channels for flowing water.
Gradient
The gradient of a river is the rate at which it loses elevation along its course. This loss determines the river’s slope, and to a large extent its rate of flow. Shallow gradients produce gentle, slow rivers while steep gradients are associated with more forceful flows.
Constrictions
Constrictions can form a water hazard where the river’s flow is forced into a narrower channel. This pressure causes the water to flow more rapidly and to react differently to the river bed.
Obstructions
A boulder or ledge in the middle of a river or near the side can obstruct the flow of the river, and can also create a “pillow”, when water flows backwards upstream of the obstruction, or a “pour over” (over the boulder), and “hydraulics” or “holes” where the river flows back on itself—perhaps back under the drop,often with fearful results for those caught in its grasp.
Water Flow
Measuring water flow is an important aspect for canyoners. A marked increase or decrease in flow can create a hazard or make safe passage through previously navigated rapids more difficult or impossible. Flow rate is measured in either Cubic Meters per Second (m³/s) or Cubic Feet per Second (cfs)