ACA Hydrology & Water Reading Flashcards
6 cards from real ACA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 ACA Hydrology & Water Reading flashcards as text
What is a 'laminar flow' in a river, and where is it most commonly found?
Answer: Smooth, parallel layers of water typically found on flat sections and near the surface in low-gradient rivers
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.
What creates a 'pillow' on the upstream face of a rock in a river?
Answer: Water deflected upward as the current piles against the upstream side of an obstacle
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.
What is the 'V' shape (downstream V) visible on the river surface, and what does it indicate?
Answer: The tongue of fast, smooth water between two obstacles, indicating the deepest and clearest channel
A downstream V (apex pointing downstream) indicates the deepest, fastest, clearest line of flow between two obstacles — the preferred route for paddlers.
What is an 'upstream V' on the river surface, and what hazard does it indicate?
Answer: A rock or obstacle just beneath the surface, with current being deflected around it
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.
What is the 'thalweg' of a river, and why is it important for paddlers?
Answer: A German term for the deepest, fastest part of the main channel — important for navigation and finding the cleanest line
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.
What does 'gradient' mean in river terminology, and how does it affect paddling difficulty?
Answer: The rate of elevation drop per mile — higher gradient generally means more technical, faster, and more challenging water
Gradient measures how steeply a river drops — rivers with high gradient drop quickly, creating rapid sequences, powerful currents, and more challenging whitewater.