Section 9

How can sediment act as a polutant?

Decreases compensation point (where O2

use exceeds production)

• Clog waterways, carry contaminants,

increase drinking water treatment cost

• Point-source discharges decreasing, but

non-point increasing (urban expansion

What does sediments do to hydroelectric turbines?

It can ruin the blades via scratching

Point source?

Comes from a set location like a pipe

Non point sources?

Comes from multiple avenues like erosion in a field.

Turbidity

Clarity of a water sample

• Amount of dissolved or suspended solids

• Suspended sand, silt or clay, organic materials/creatures

Turbidimetry

Measures the decrease in transmitted light intensity as it passes

through a sample containing particles (180* angle)

when to use turbidimetry

Suitable for samples with higher concentrations of larger particles, where a

significant amount of light is blocke

Nephelometry

Measures the intensity of light that is scattered by particles in the solution at

an angle to the incident beam (typically 90 degrees)

How doe nephelometry measure?

It measures scattered light

What is more sensitive, turbidimeter or nephelometer

nephelometer is more senstive but it requires carful minerology considerations

Secchi disk

20 cm disk lowered into stream until you can no longer see it

Is high turbity good?

No, it increases algae growth and lower fish food

Hydrometer for Total Suspended Solids (TSS)

Measures density of the sediment suspension

• Density increases as the sediment

concentration increase

Bedload transport

is sediment that is transported along

or near the streambed

• Larger than suspended solids and either roll or

bounce along the stream be

Where do you measure sediments?

At eroding source

– At boundary of disturbed area

– At some point downstream of disturbed area

How can you compare sediments?

Use total suspended solids and turbidity