ACA Hydrology & Water Reading Flashcards
6 cards from real ACA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 ACA Hydrology & Water Reading flashcards as text
What is a 'strainer' in river paddling, and why is it one of the most dangerous hazards?
Answer: An obstacle (such as a fallen tree) that allows water to pass through but traps boats and people, creating a drowning risk
A strainer is any obstacle — typically a fallen tree or debris pile — where water flows through gaps but a boat or paddler's body is pinned against it by the current's force.
What is a 'sieve' in whitewater, and how does it differ from a strainer?
Answer: A sieve is a submerged rock formation with narrow gaps that water passes through, trapping swimmers underwater; a strainer is usually surface debris
A sieve consists of submerged boulders with gaps through which water flows — a swimmer can be forced underwater and pinned against the rocks, with no surface visibility for rescuers.
What does 'water temperature stratification' mean for paddlers on large lakes and reservoirs?
Answer: Warm surface water sits above cold deep water, creating a thermocline — cold shock risk is high if paddlers capsize into cold underlying water
In thermally stratified water bodies, the cold deep layer can cause cold shock and hypothermia within minutes even when the surface layer feels comfortable.
What is 'flood pulse' and how should an ACA instructor account for it in trip planning?
Answer: The natural seasonal rise and fall of river levels caused by precipitation or snowmelt, which changes river character dramatically
Flood pulse refers to seasonal high-water events that can dramatically increase current speed, debris load, water temperature, and overall hazard — requiring reassessment of previously known routes.
What is the significance of a 'wave train' in a rapid?
Answer: A series of standing waves created by fast water flowing over a regular bottom feature, indicating a clear but bumpy route
A wave train is a series of regular standing waves in the main flow — it usually indicates a clear channel free of submerged obstacles, though it can be turbulent.
What is a 'pourover' in whitewater, and how does it affect swimability?
Answer: Water pouring off a ledge or underwater shelf, often creating a strong recirculating hydraulic that is difficult to escape by swimming
A pourover occurs when water pours over a ledge into a recirculating hole below — these hydraulics can be extremely retentive and difficult to swim out of.