ACA ACA Hydrology & Water Reading

Question 1

What is a 'laminar flow' in a river, and where is it most commonly found?

Accepted Answer

Smooth, parallel layers of water typically found on flat sections and near the surface in low-gradient rivers

Answer

Laminar flow is smooth, layered water movement where water molecules travel in parallel paths — it occurs on flat, slow sections and is the opposite of turbulent flow.

Question 2

What creates a 'pillow' on the upstream face of a rock in a river?

Accepted Answer

Water deflected upward as the current piles against the upstream side of an obstacle

Answer

A pillow is a mound of water pushed upward on the upstream side of a submerged or surface rock as the current is deflected around the obstacle.

Question 3

What is the 'V' shape (downstream V) visible on the river surface, and what does it indicate?

Accepted Answer

The tongue of fast, smooth water between two obstacles, indicating the deepest and clearest channel

Answer

A downstream V (apex pointing downstream) indicates the deepest, fastest, clearest line of flow between two obstacles — the preferred route for paddlers.

Question 4

What is an 'upstream V' on the river surface, and what hazard does it indicate?

Accepted Answer

A rock or obstacle just beneath the surface, with current being deflected around it

Answer

An upstream V (apex pointing upstream) indicates a submerged obstacle — current is being deflected to either side, creating a V shape with the point toward the hazard.

Question 5

What is the 'thalweg' of a river, and why is it important for paddlers?

Accepted Answer

A German term for the deepest, fastest part of the main channel — important for navigation and finding the cleanest line

Answer

The thalweg is the line of deepest flow in a river channel — paddlers follow it to find the fastest current and avoid grounding on shallow features.

(ACA) American Canoe Association Instructor Certification Practice Test

(ACA) American Canoe Association Instructor Certification Practice Test

ACA ACA Hydrology & Water Reading