Certified Storm Water Operator Practice Exam

Which factors influence the rate at which transported particles settle out?

1. Size, shape, and temperature of water

2. Color, texture, and age

3. Size, shape, and density of the transported particles

4. Moisture content, pH levels, and biological activity

The correct answer is: Size, shape, and density of the transported particles

The rate at which transported particles settle out of water is influenced primarily by the size, shape, and density of the particles themselves. Larger particles typically settle faster due to the increased gravitational force acting upon them, while smaller particles may remain suspended in the water column longer because they can be more easily influenced by current and turbulence. The shape of the particles also plays a crucial role; for instance, flat or irregularly shaped particles may settle more slowly than spherical ones of the same size because their surface area affects how they interact with the surrounding fluid. Density is another critical factor, as higher-density particles will settle more quickly compared to lower-density particles of the same size and shape, given that they have a greater gravitational pull relative to their buoyancy. While the other choices mention various factors like moisture content and biological activity, these do not directly relate to the settling rates of particles in the same way that the intrinsic characteristics of the particles do. Factors such as temperature, while potentially affecting fluid viscosity and thus indirectly influencing settling rates, do not change the fundamental properties of the particles that primarily determine their settling velocity.