ACA ACA Hydrology & Water Reading 2 — Questions and Answers
Question 1: What is a 'strainer' in river paddling, and why is it one of the most dangerous hazards?
- A shallow section of river where rocks scrape the bottom of the hull
- An obstacle (such as a fallen tree) that allows water to pass through but traps boats and people, creating a drowning risk (Correct answer)
- A narrow canyon section with fast, constricted current
- A series of closely spaced standing waves
Correct 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.
Question 2: What is a 'sieve' in whitewater, and how does it differ from a strainer?
- A sieve is a large hole in the riverbed; a strainer is a surface hazard
- A sieve is a submerged rock formation with narrow gaps that water passes through, trapping swimmers underwater; a strainer is usually surface debris (Correct answer)
- There is no difference — the terms are interchangeable
- A sieve is a shallow riffle; a strainer is a deep hole
Correct 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.
Question 3: What does 'water temperature stratification' mean for paddlers on large lakes and reservoirs?
- Water at different depths has different currents that create navigation challenges
- Warm surface water sits above cold deep water, creating a thermocline — cold shock risk is high if paddlers capsize into cold underlying water (Correct answer)
- Temperature stratification prevents waves from forming on flat water
- Different water temperatures are used to rate the difficulty of lake crossings
Correct 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.
Question 4: What is 'flood pulse' and how should an ACA instructor account for it in trip planning?
- The rhythmic wave created by dam releases on regulated rivers
- The natural seasonal rise and fall of river levels caused by precipitation or snowmelt, which changes river character dramatically (Correct answer)
- The pulse rate increase experienced by paddlers in cold water
- A paddling technique for crossing flood-swollen rivers
Correct 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.
Question 5: What is the significance of a 'wave train' in a rapid?
- A series of buses used to shuttle paddlers to the put-in
- A series of standing waves created by fast water flowing over a regular bottom feature, indicating a clear but bumpy route (Correct answer)
- Waves that travel upstream against the current
- A training exercise where paddlers follow each other through a wave sequence
Correct 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.
Question 6: What is a 'pourover' in whitewater, and how does it affect swimability?
- Water pouring off a ledge or underwater shelf, often creating a strong recirculating hydraulic that is difficult to escape by swimming (Correct answer)
- A gentle overflow from a calm pool into a lower section
- A wave that breaks over the bow of a kayak
- The overflow from a dam spillway into the river below
Correct 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.
ACA ACA Hydrology & Water Reading 2
What is a 'strainer' in river paddling, and why is it one of the most dangerous hazards?