Certified Storm Water Operator Practice Exam

What type of particles are often transported easily and settle slowly?

1. Silt-sized particles

2. Fine sand-sized particles

3. Clay-sized particles

4. Gravel-sized particles

The correct answer is: Clay-sized particles

Clay-sized particles are known for being extremely small, often measuring less than 0.002 mm in diameter. This small size allows them to remain suspended in water for extended periods, making them easily transportable by flowing water. Because of their diminutive size and low settling velocity, clay particles take a long time to settle out of suspension when conditions change. This characteristic is significant in stormwater management, as it indicates that clay can remain in the water column, contributing to turbidity and potentially affecting water quality. In contrast, larger particles like gravel-sized ones settle quickly due to their weight, and fine sand-sized particles settle faster than clay but slower than gravel. Silt-sized particles, while more easily transported than sand or gravel, do not exhibit the same prolonged suspension characteristics as clay. Thus, clay-sized particles epitomize the type of particles that settle slowly despite being transported easily.