SRT Upstream & Downstream Hazard ID 3 â Questions and Answers
Question 1: Which characteristic most distinguishes a 'keeper' hydraulic from a non-keeper hole?
- A keeper has steep side walls and no lateral escape route on either bank
- A keeper recirculates objects back into the trough rather than flushing them downstream (Correct answer)
- A keeper has a longer wave train and higher aerated foam pile
- A keeper is always formed below vertical drops exceeding 6 feet
Correct answer: A keeper recirculates objects back into the trough rather than flushing them downstream
A keeper hydraulic recirculates objectsâincluding swimmersâback into the trough due to the geometry of the backwash, making escape extremely difficult.
Question 2: From upstream, what distinguishes a standing wave from a hydraulic (hole) in terms of visual appearance?
- Standing waves have white foam piles; holes have smooth, glassy crests
- Standing waves show continuous downstream-moving crests; holes show a recirculating foam pile with a trough (Correct answer)
- Standing waves are formed only in Class IâII water; holes only in Class IVâV
- Standing waves are wider than the river channel; holes are narrow features
Correct answer: Standing waves show continuous downstream-moving crests; holes show a recirculating foam pile with a trough
Standing waves move water downstream continuously, while holes display a recirculating foam pile and visible trough where water cycles back upstream.
Question 3: A 'pourover' feature is hazardous primarily because:
- The smooth water on approach conceals depth, making foot placement uncertain
- Water pours over a ledge and creates a recirculating hydraulic trough below (Correct answer)
- Pourover rocks are always undercut, creating a pinning hazard for boats only
- The wave train below a pourover extends 50+ meters, exhausting swimmers
Correct answer: Water pours over a ledge and creates a recirculating hydraulic trough below
Water pouring over a ledge accelerates and plunges into a pool, creating a recirculating trough that can trap and recirculate swimmers.
Question 4: Which river feature is described as a 'hydraulic' versus a 'stopper' in swiftwater rescue terminology?
- They are entirely different hazards; a stopper is always upstream of a hydraulic
- The terms are often used interchangeably for a recirculating hole feature; 'stopper' emphasizes its ability to halt downstream progress (Correct answer)
- A stopper refers to a strainer; a hydraulic refers to a wave feature only
- Hydraulics form only below dams; stoppers form only below natural ledges
Correct answer: The terms are often used interchangeably for a recirculating hole feature; 'stopper' emphasizes its ability to halt downstream progress
Both terms describe recirculating holes; 'stopper' is commonly used in British/European contexts and emphasizes the feature's ability to stop and retain swimmers or boats.
Question 5: An undercut rock is particularly dangerous because:
- It creates a strong surface eddy that traps swimmers in a circular pattern
- Current flows beneath the rock, creating a void that can trap and pin a swimmer with no escape (Correct answer)
- It always produces a visible boil on the downstream surface identifying its location
- Undercuts only affect paddlecraft and pose minimal risk to swimmers
Correct answer: Current flows beneath the rock, creating a void that can trap and pin a swimmer with no escape
Undercut rocks have cavities beneath them where current flowsâa trapped swimmer is pinned by hydraulic force with no upstream or downstream exit.
Question 6: When prioritizing between a strainer and a hydraulic encountered simultaneously in a rescue corridor, which general principle applies?
- Hydraulics are always treated first because recirculation is more immediately fatal
- Strainers are typically prioritized because entrapment with water pressure is almost always fatal with minimal survival window (Correct answer)
- Priority depends solely on the victim's current position relative to each hazard
- Both hazards are equal priority; throw rope to victim regardless of feature type
Correct answer: Strainers are typically prioritized because entrapment with water pressure is almost always fatal with minimal survival window
Strainers pin victims with the full force of the current against them with almost no survivable position, giving rescuers an extremely short time window compared to hydraulic recirculation.
Question 7: The recirculating backwash pattern of a low-head dam's hydraulic trough is sometimes called 'a drowning machine' because:
- Its gentle surface appearance lures swimmers into a strong whirlpool current
- The surface recirculation returns swimmers to the boil line repeatedly while the sub-surface current prevents escape (Correct answer)
- Dam operators increase discharge during rescues, making conditions unpredictable
- Its aerated water reduces buoyancy and causes PFDs to fail
Correct answer: The surface recirculation returns swimmers to the boil line repeatedly while the sub-surface current prevents escape
The surface water recirculates back into the trough while sub-surface currents prevent swimming out, trapping victims in a near-endless cycle.
SRT Upstream & Downstream Hazard ID 3
Which characteristic most distinguishes a 'keeper' hydraulic from a non-keeper hole?