ACA ACA Water Reading & River Hydrology 1 — Questions and Answers
Question 1: What is a 'hydraulic' (also called a 'hole') in river hydrology?
- A submerged rock that causes eddies
- A recirculating feature where water flows back upstream after dropping over an obstacle (Correct answer)
- A fast laminar flow channel between rocks
- A calm pool at the bottom of a rapid
Correct 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.
Question 2: What is the function of an 'eddy' in river paddling?
- A downstream current that accelerates boat speed
- A calm, upstream-flowing area behind an obstacle used for resting or scouting (Correct answer)
- A surface wave caused by wind
- A drop in water level indicating a waterfall
Correct 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.
Question 3: What does the term 'gradient' mean in river classification?
- The width of the river at its widest point
- The vertical drop per horizontal distance, usually measured in feet per mile (Correct answer)
- The temperature change across a river section
- The ratio of flatwater to rapids in a stretch
Correct 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.
Question 4: According to ACA water reading instruction, what does a 'V' shape pointing downstream on the river surface indicate?
- A submerged hazard below the surface
- A clear channel of deeper, faster water between obstacles (Correct answer)
- An approaching hydraulic feature
- Shallow water over a gravel bar
Correct 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.
Question 5: What is 'strainer' as taught in ACA river hydrology?
- A rock garden requiring technical maneuvering
- Debris such as branches or logs through which water flows but a paddler cannot pass safely (Correct answer)
- A shallow riffle section of a river
- A whirlpool formed by converging currents
Correct 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.
Question 6: How does water volume affect river hazard levels as taught in ACA instructor courses?
- Higher volume always makes rivers safer by washing hazards away
- Higher volume increases current speed and hydraulic power, making features more dangerous (Correct answer)
- Volume has no effect on hazard level
- Lower volume always increases danger by exposing more rocks
Correct 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.
ACA ACA Water Reading & River Hydrology 1
What is a 'hydraulic' (also called a 'hole') in river hydrology?