Measuring Average Bedload Size

Equipment needed

(Caliper)

Quadrat

Caliper

Record sheet

Pencil

Procedure

Standing in the river, drop a quadrat onto the ground or into the water and allow it to settle. Select any pebble within the range of the quadrate. Fit the pebble horizontally (i.e. on its longest axis) in the gap of the caliper and take a reading of the length. Record the value. Rotate the pebble until it is vertical (i.e. on its middle axis) and take a reading of the length. Record the value. Repeat steps 2 to 5 until you have found the average bed load size of as many pebbles as you need to obtain your desired degree of reliability.

Measuring Channel Features (Width, Depth, Velocity, Discharge)

Width

Extend a tape measure from the point where the dry bank meets the water on one side of the river to the same point on the other side (hold it taut about 20cm above water level). Record the length, viewing the reading from directly above the tape measure.

Average depth (across channel)

Immerse a metre ruler (edge facing upstream to minimize exposure to flowing water) into the water until it just touches the riverbed. Record the distance from the bed to the water surface. Repeat at regular intervals (e.g. every 50cm) across the channel.

Velocity

Measure a set distance of the river (up to 10m). Mark the start and end points. Put the float (i.e. a brightly coloured object that floats in water) slightly upstream of the start point. With a stopwatch, time how long it takes the float to travel from start to end. Repeat at least five times, releasing the float at regular intervals across the stream to measure velocity across the channel. Disregard any anomalous results (e.g. if the float gets stuck).

Discharge (cumecs or cubic metres per second)

Multiply the cross-sectional area* (square metres) by its velocity (m/s)

*width x depth

 

 

Fieldwork: Water Testing

pH level

Collect a water sample. Dip a dry strip of litmus paper into the sample. Leave for a few minutes or until the litmus paper has changed colour. Compare the new colour of the litmus paper to the pH colour chart (any number below 7 is acidic, any number above is alkaline).

Nitrate level

Collect a water sample. Put about 2.5ml of the water into a test tube. Add an equal volume of nitrate-reducing reagent. Cover and shake the test tube until the contents are fully combined. Observe the colour of the mixture and compare it to the colour chart in the nitrate testing kit – from this you can approximate the nitrate concentration of the water sample in mg/L.

Turbidity

Secchi disk method (in a deeper part of the river)

Slowly lower the Secchi disk into the water and stop just when you can no longer see it. Record the depth (indicated by marks on the rope). Slowly raise the disk until it can just be seen again. Record the depth. Find the mean of these two depths to determine the Secchi depth.

Reagent test method

Collect a water sample. Compare the turbidity to a control solution of equal volume. Gradually add a turbidity reagent to the control sample until it is visually identical the water sample. A value can be determined in standard Jackson Turbidity Units.

Odor

Threshold Odour Test:

Collect a water sample. Add odorless water to the sample and stop when the sample itself is odorless. The last dilution before the sample becomes odorless determines the Threshold Odor Number (TON), which measures how much odor was present.