Gravel size is primarily measured and classified by its particle size range. This method involves sorting or analyzing particles based on their diameter or range of diameters.
Understanding Gravel Classification
Gravel is not a single size but encompasses a range of granular materials. Classification scales categorize these materials into different groups based on specific size boundaries. These classifications can range from very fine particles (like granules) up to much larger fragments (like boulders), with gravel typically falling within an intermediate range.
The Udden-Wentworth Scale
One common system for classifying sediment sizes, including gravel, is the Udden-Wentworth scale. In this scale, gravel is broken down into more specific categories based on measured size ranges.
Here's how the Udden-Wentworth scale defines two common types of gravel based on size:
| Gravel Type | Millimeter (mm) Range | Inches (in) Range |
|---|---|---|
| Granular | 2–4 mm | 0.079–0.157 in |
| Pebble | 4–64 mm | 0.2–2.5 in |
As shown in the table derived from the reference, granular gravel includes particles from 2 mm up to 4 mm, while pebble gravel covers a broader range from 4 mm up to 64 mm. Larger particle sizes within the broader gravel classification might extend up to cobbles and boulders in this scale.
Therefore, measuring gravel size involves determining where individual particles or a sample of particles fall within these established size ranges using methods like sieving or visual inspection against a scale.
