SRT Hydrology and River Hazards 2 — Questions and Answers
Question 1: What term describes the volume of water flowing past a fixed point per unit of time in a river?
- Velocity
- Discharge (Correct answer)
- Gradient
- Stage
Correct answer: Discharge
Discharge, measured in cubic feet per second (cfs) or cubic meters per second, is the volume of water moving past a point per unit time.
Question 2: A 'hole' or hydraulic on a river is created when water flows over a submerged obstruction and recirculates. Which current characterizes the surface flow of a hydraulic?
- Downstream at the surface
- Upstream at the surface toward the obstruction (Correct answer)
- Laminar flow parallel to the bank
- Downward spiral toward the riverbed
Correct answer: Upstream at the surface toward the obstruction
In a hydraulic, surface water flows back upstream toward the obstruction, creating a recirculating trap for swimmers and boats.
Question 3: What is the 'tongue' of a rapid?
- A submerged rock shelf extending from the bank
- The smooth V-shaped downstream-pointing current between obstacles (Correct answer)
- A lateral wave formed by converging currents
- A pillow of water on the upstream face of a rock
Correct answer: The smooth V-shaped downstream-pointing current between obstacles
The tongue is the smooth, V-shaped chute of fast water pointing downstream that indicates the deepest, least obstructed channel through a rapid.
Question 4: Which factor most directly causes an increase in a river's erosive power during flood conditions?
- Decreased water temperature
- Increased sediment load only
- Exponential increase in velocity and discharge (Correct answer)
- Flattening of the river gradient
Correct answer: Exponential increase in velocity and discharge
During floods, both velocity and discharge increase dramatically, and erosive power increases exponentially with velocity (proportional to velocity squared or greater).
Question 5: What is a 'strainer' in swiftwater rescue terminology?
- A tool used to filter debris from a rope system
- An obstruction that allows water through but traps solid objects (Correct answer)
- A type of hydraulic found below dams
- A low-head dam with grating on the downstream face
Correct answer: An obstruction that allows water through but traps solid objects
A strainer is any obstacle (such as a downed tree or debris pile) that allows water to pass through but traps swimmers, boats, or rescue personnel.
Question 6: The international whitewater classification scale rates rivers from Class I to Class VI. What does a Class V rapid indicate?
- Flat water with occasional riffles
- Moderate rapids with waves, easy to navigate
- Extremely difficult, violent, and unpredictable water requiring expert skill (Correct answer)
- Unrunnable water with extreme danger to life
Correct answer: Extremely difficult, violent, and unpredictable water requiring expert skill
Class V rapids are rated as extremely difficult, featuring violent, unpredictable water with serious hazards requiring expert skill and excellent swiftwater rescue training.
Question 7: What is the primary hazard created by a low-head dam for a swimmer or boater?
- Increased surface turbulence preventing breathing
- A highly aerated water column reducing buoyancy in a recirculating hydraulic (Correct answer)
- Sudden depth increase on the downstream side
- Strong lateral currents pulling toward the bank
Correct answer: A highly aerated water column reducing buoyancy in a recirculating hydraulic
Low-head dams create a uniform hydraulic with highly aerated, recirculating water that reduces buoyancy and makes self-rescue extremely difficult, often described as 'drowning machines.'
SRT Hydrology and River Hazards 2
What term describes the volume of water flowing past a fixed point per unit of time in a river?