ACA Water Reading & River Hydrology Flashcards

What is a 'hydraulic' (also called a 'hole') in river hydrology?

Answer: A recirculating feature where water flows back upstream after dropping over an obstacle

A hydraulic or hole forms when water drops over a ledge or rock and recirculates back toward the feature, creating a powerful backwash.

What is the function of an 'eddy' in river paddling?

Answer: A calm, upstream-flowing area behind an obstacle used for resting or scouting

An eddy is a calm pocket of water that flows upstream behind rocks or other obstacles, used by paddlers to rest, regroup, or scout downstream.

What does the term 'gradient' mean in river classification?

Answer: The vertical drop per horizontal distance, usually measured in feet per mile

Gradient describes how steeply a river drops, expressed in feet per mile, and is a primary factor in determining current speed and rapid intensity.

According to ACA water reading instruction, what does a 'V' shape pointing downstream on the river surface indicate?

Answer: A clear channel of deeper, faster water between obstacles

A downstream-pointing 'V' on the water surface marks a tongue of clear water flowing between obstacles, indicating the preferred entry line into a rapid.

What is 'strainer' as taught in ACA river hydrology?

Answer: Debris such as branches or logs through which water flows but a paddler cannot pass safely

A strainer is any obstruction like logs, wire fences, or debris that allows water to flow through but traps and can pin a swimmer or boat against it.

How does water volume affect river hazard levels as taught in ACA instructor courses?

Answer: Higher volume increases current speed and hydraulic power, making features more dangerous

Higher water volume amplifies current speed and hydraulic power, making existing features such as holes and strainers significantly more dangerous.