SRT Upstream & Downstream Hazard ID 2 — Questions and Answers
Question 1: A rescuer standing on the bank sees a 'horizon line' across the river ahead. What does this indicate?
- A safe, wide pool suitable for victim recovery
- A drop or significant change in gradient that may conceal a hazard (Correct answer)
- A shallow riffle with minimal current speed
- An eddy line where calm water meets the main current
Correct answer: A drop or significant change in gradient that may conceal a hazard
A horizon line—where the river surface disappears from view—signals a drop, falls, or hydraulic feature that must be scouted before approach.
Question 2: Pillow water forming on the upstream face of a submerged rock is a useful indicator because it shows:
- The rock is deep enough to safely paddle over
- Water is deflecting off the obstacle, signaling a sub-surface hazard (Correct answer)
- A clean hydraulic that will flush swimmers downstream
- Strong upwelling that indicates a safe recovery eddy
Correct answer: Water is deflecting off the obstacle, signaling a sub-surface hazard
Pillow water is created when current hits an obstacle and deflects upward, warning rescuers of a submerged or partially submerged object.
Question 3: Which visual characteristic most reliably identifies a low-head dam from an upstream river approach?
- A V-shaped tongue of smooth water pointing downstream
- A uniform, horizon-wide line of white water with a glassy lip above it (Correct answer)
- Highly turbulent, chaotic wave trains with irregular spacing
- A wide, deep pool with slow surface current and boiling upwellings
Correct answer: A uniform, horizon-wide line of white water with a glassy lip above it
Low-head dams present a uniform, wall-to-wall horizon line with a deceptively smooth glass lip above the recirculating trough.
Question 4: A rescuer observes boils and upwelling on the river surface in what appears to be flat water. This most likely indicates:
- Safe swimming conditions with oxygenated water
- Sub-surface turbulence from submerged structures, rocks, or hydraulics (Correct answer)
- A productive location for victim self-rescue due to upward water movement
- Normal laminar flow transitioning to a pool
Correct answer: Sub-surface turbulence from submerged structures, rocks, or hydraulics
Boils and upwellings on the surface reflect sub-surface turbulence—often caused by submerged boulders, bridge footings, or hydraulic backwash.
Question 5: When assessing river gradient, a steeper gradient generally means:
- Lower current velocity and reduced hydraulic hazard
- Higher current velocity and increased potential for dangerous hydraulics (Correct answer)
- More predictable laminar flow patterns suitable for entry
- Reduced strainer risk due to faster debris transport
Correct answer: Higher current velocity and increased potential for dangerous hydraulics
Steeper gradient increases current velocity, which amplifies the force and danger of hydraulics, strainers, and impact with obstacles.
Question 6: A rescuer approaching a hazardous feature cannot see it clearly due to sun glare, but what auditory cue would most strongly suggest a significant hydraulic ahead?
- A high-pitched bubbling sound consistent with riffles
- A low, continuous roaring sound that increases in volume with proximity (Correct answer)
- The absence of sound indicating calm, deep water
- Intermittent splashing sounds from surface waves
Correct answer: A low, continuous roaring sound that increases in volume with proximity
A sustained, low roar that grows louder is characteristic of large hydraulics, falls, or significant drops and warrants immediate scouting.
Question 7: When scouting a rapid from shore, the best position to identify downstream hazards is:
- Directly at the water's edge at the entry point, looking downstream
- Well above the feature, moving to multiple vantage points at river level (Correct answer)
- From the highest available elevation regardless of distance from the river
- Only from the river right bank, as current always favors river left
Correct answer: Well above the feature, moving to multiple vantage points at river level
Moving to multiple shore-level vantage points along the feature gives the most complete hazard picture—elevation alone creates blind spots in the hydraulic profile.
SRT Upstream & Downstream Hazard ID 2
A rescuer standing on the bank sees a 'horizon line' across the river ahead.
What does this indicate?