IGCSE Geography- River Fieldwork

Cross section area of river channel

Width x depth

Velocity

distance/time

Cross section area of river channel

Width x depth

Velocity

distance/time

Discharge

The amount of water flowing past a particular point in the river.

- area of cross section of river x velocity (cumecs m^3/sec)

Wetted perimeter

Total length of a river's bed and banks which are in contact with water.

Sampling

Number of sample sites should be large enough to be able to use statistical tests and obtain meaningful, accurate results.

Random sampling

Each site of the river has an equal chance of being collected.

Systematic sampling

A rule of procedure is used for selection (e.g. every 100 meters) to avoid bunching of data points.

Stratified sampling

Most accurate method, as it involves looking at the area and dividing it into categories (e.g. Rock type, elevation and gradient).

The size of each category ( as a % of a whole) determines the number of samples taken from the category. The samples may be selected randomly or systematically.

Pragmatic sampling

Used in areas where access is difficult or local conditions mean obvious difficulties are going to interfere with the data collection (e.g. river is too dangerous or inaccessible).

Measuring channel width

This is measured using a tape measure stretched across the channel. Measure the width across the surface of the water, stretched tight, and standing at each side of the river.

Measuring channel depth

Take the width of the channel and divide it into 10 equal parts. Measure the depth at each of the ten points across the channel. Always start from the same side, left or right when looking downstream.

Measuring the wetted perimeter

Lay the chain along the river bed at the same place as you measured the channel width. The chain is heavy and flexible, so it sinks to the bottom over the uneven bottom of the channel. Mark where it touches the water on each bank and remove the chain. Lay the chain on the river bank and use a tape measure to measure the length of the chain, which was in contact with the water.

Measuring velocity

Measure a distance of 10 meters downstream, marking each end with a ranging pole. Release the floating device gently and use the stopwatch to time the floating device traveling over the distance. Repeat this three times for an accurate result. Then carry out it in different parts of the river (left, right, middle)

Using a flowmeter

Flowmeter is placed underwater and the results are shown on the device. The propeller must be facing upstream, allowing the water to flow through.

Measuring gradient

Take two ranging poles and place them in the channel at a distance of 10 meters apart, holding them at water level. Use a clinometer to measure the angle between them by lining up the same height at each pole. Measure the angle three times at different parts of the river to receive more accurate results.

Measuring sediment size

Large pieces of sediment can be measured by a caliper for their width, length and thickness (long axis, short axis, side axis).

Measuring sediment shape

Particle shape is measured by observation. A random sample of sediment (10 pieces) is taken and the number of particles of different shapes and of particular roundness is recorded. The Power's scale of roundness is used.