IGCSE Geography Paper 4 (River measurement)

Key Concepts

River characteristics (discharge, width, depth, velocity, load), fieldwork site selection criteria (accessibility, safety, human impact, turbulent flow), safety precautions, river gradient measurement, river depth measurement, river width measurement, river velocity measurement (floater method, flow meter method), infiltration rate measurement.

River Characteristics and Measurement

Rivers flow from upstream to downstream, and several characteristics change along this course.

• Discharge: Increases downstream.
• Width: Increases downstream (distance between banks).
• Depth: Increases downstream (distance from surface to riverbed).
• Velocity: Increases downstream.
• Load Quality (amount of load): Increases downstream.
• Load Particle Size: Increases upstream.
• Channel Bed Roughness: Increases upstream.
• Slope Angle/Gradient: Increases upstream.

Fieldwork Site Selection Criteria

When choosing a site for river investigation, consider the following:

1. Accessibility: Easy transport of equipment from school or road.
2. Safety:
   • Strength of the current (avoid fast-flowing rivers).
   • Presence of dangerous animals.
   • Sharp rocks (risk of slipping).
3. Human Impact: Avoid areas with dams or other alterations, as data will be affected.
4. Turbulent Flow: Avoid waterfalls and rapids, as they affect readings.

Safety Precautions

• Suitable Clothing: Wear appropriate footwear (walking boots).
• Group Work: Always go in groups.
• Sunglasses: Protect eyes from sun rays.
• Weather Forecast: Check for rainstorms.
• Post-Rainfall: Do not enter the river after heavy rainfall.
• Mobile Phones: Carry for communication.

Measuring River Gradient (River Profile)

Instruments: Tape measure, ranging poles, string, clinometers, recording sheet.

Steps:

1. Measure a set distance apart (e.g., 10 meters) using a tape measure.
2. Students hold ranging poles at either end of the measured distance, ensuring they are vertical.
3. Place a string at the same height between the poles.
4. A student uses a clinometer to sight the top of the other ranging pole (where the string is) and takes a reading in degrees.
5. Repeat the process along the riverbed, moving from upstream to downstream.
6. Plot the data on a graph to visualize the river profile.

Measuring River Depth

Instruments: Meter rule.

Steps:

1. Place the meter rule into the river until it touches the riverbed, ensuring it is upright and vertical.
2. Record the distance between the riverbed and the surface of the water.
3. Repeat this measurement at regular intervals across the width of the river (from one bank to the other).
4. Add all the depth measurements together and divide by the number of recordings to get the average depth at that point.

Measuring River Width

Instruments: Ranging poles, measuring tape.

Steps:

1. Place ranging poles on opposite banks of the river.
2. Use a measuring tape to measure the distance between the two ranging poles, ensuring the tape is stretched out and the poles are directly across from each other (90 degrees).
3. Repeat the measurement at different sites along the river to observe changes in width.

Reasons for Increased Width and Depth Downstream:

• Increase in discharge or volume of flow, leading to more erosion of the bed and banks.
• Presence of tributaries joining the main river.
• Erosion processes (abrasion, corrosion, hydraulic action).
• Weaker Bedrock leading to increased erosion.
• Human interference with the river channel.

Measuring River Velocity

Method 1: Using a Floater

Instruments: Stopwatch, ranging poles, meter rule/tape measure, floater (e.g., orange peel).

Steps:

1. Measure a fixed distance along the river (e.g., 10 meters) using ranging poles and a tape measure.
2. Place a floater (e.g., orange peel) in the river upstream of the first ranging pole.
3. Start the stopwatch when the floater passes the first ranging pole.
4. Stop the stopwatch when the floater passes the second ranging pole.
5. Record the time taken for the floater to travel the fixed distance.
6. Repeat the method at different points across the river.

Method 2: Using a Flow Meter

Instruments: Flow meter.

Steps:

1. Place the flow meter below the water surface, ensuring the propeller faces upstream (against the current).
2. Read the speed of the river on the digital scale of the flow meter.
3. Repeat the reading at different points across the channel to get an average velocity.

Measuring Infiltration Rate

Instruments: Perforated measuring tube, water, stopwatch.

Steps:

1. Insert the measuring tube into the soil.
2. Pour water into the measuring tube.
3. Measure the height of the water in the tube.
4. Start the stopwatch and measure the height of the water in the tube every minute.
5. Record the time it takes for a specific volume of water to infiltrate into the soil.

Synthesis/Conclusion

The video provides a practical guide to conducting river investigations for IGCSE Geography Paper 4. It covers essential aspects such as site selection, safety, and detailed methodologies for measuring key river characteristics like gradient, depth, width, velocity, and infiltration rate. The emphasis on specific instruments, step-by-step instructions, and explanations of underlying processes makes it a valuable resource for students undertaking fieldwork.