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

Turbulent, chaotic flow in the center of a rapid

Answer

The circular current in an eddy

Answer

The underwater current that runs opposite to surface 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

Sediment deposited by slow-moving water

Answer

An air pocket trapped beneath the rock's surface

Answer

A wave formed when fast water meets a calm pool

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 hydraulic or hole that traps swimmers

Answer

A sand bar running along the river bottom

Answer

The wake created by a powerboat upstream

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

Safe passage between two eddies

Answer

A smooth water entry into a pool below a rapid

Answer

The calm water at a river bend

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 shallow area along the riverbank where portaging is easiest

Answer

A measurement of total river gradient over a given distance

Answer

The boundary between fast and slow water in an eddy

Question 6

What does 'gradient' mean in river terminology, and how does it affect paddling difficulty?

Accepted Answer

The rate of elevation drop per mile — higher gradient generally means more technical, faster, and more challenging water

Answer

The color change in water indicating depth changes

Answer

The temperature differential between surface and deep water

Answer

The ratio of sand to rock in the riverbed composition