How to Calculate Suspended Sediment Load

Written by alex zang
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Rock, dirt, and clay are all types of sediment. When a river flows over any of these materials, it may pick them up and carry them down stream. This is known as suspended sediment. Scientists can find the sediment load of a river and can use that number to figure out what type of impact people are having in that environment, as construction going on upstream will impact the suspended sediment load. The formula for figuring out the sediment load of a river is: sediment concentration (SC) multiplied by stream discharge (D) equals sediment load.

Skill level:
Moderately Challenging

Things you need

• Wide mouth flasks
• Filter paper
• Electronic scale
• Funnel
• Flow meter w/ wading rod
• Measuring tape or meter stick

Find Sediment Concentration

1. 1

Use a wide-mouthed flask to to collect water samples from the river. Get your samples from several different locations on the river and during different times -- ideally a few weeks apart. This will yield a more accurate sediment concentration number.

2. 2

Measure the weight of your filter paper (each filter separately). You'll need to subtract this number from your total to find an accurate sediment concentration number. Given the light weight of filter paper, you'll likely need an electronic scale to do this.

3. 3

Pour each sample through a funnel with a filter in it, being sure to change to a new filter paper each time you switch samples. After the water has been filtered, measure it to figure out the volume of water for each sample.

4. 4

Dry your filters, either by letting them sit or putting them in a drying oven.

5. 5

Weigh each filter with the sediment. To find the mass of the sediment, subtract the weight of the filter paper from the weight of the sediment.

6. 6

Find the sediment concentration (SC) by dividing the mass of the sediment by the volume of water for each sample. Average all of your results together to find the average sediment concentration of the river.

Find Stream Discharge

1. 1

Figure out the area of the stream's cross section at the points you took samples from. To do this, measure the width of the stream, then create several equal sections. For example, if the stream is 5 meters wide, you would create five 1 meter sections. Take the length of the segment (in this example 1 meter) and multiply by the depth of each segment to get the area. Take the area of each cross section and add them together. This will give you the total area of your stream's cross section.

2. 2

Use a flow meter and a wading rod to find the velocity at the centre of the river's flow.

3. 3

Find each segment's discharge by multiplying the segment's area with the segment's discharge. Add all of the segment discharge numbers together to find the total river discharge.

4. 4

Find the sediment load of your river by multiplying your discharge with the sediment concentration number that you calculated in section one. After you're finished, you'll know the sediment load of your river.

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