Physical Fieldwork Methods (Rivers/Coasts)

Purpose of Physical Fieldwork

Physical fieldwork in rivers and coastal environments is carried out to investigate natural processes shaping the landscape. It involves collecting primary data directly from the environment to gain a better understanding of features such as river channels, sediment distribution, and coastal profiles. Fieldwork helps test hypotheses about how physical processes like erosion, transportation, and deposition operate in real settings.

For example, you might hypothesise that river velocity increases downstream or that sediment size decreases along the beach from the backshore to the foreshore. Fieldwork allows you to collect evidence to support or refute these ideas, making geographical understanding more accurate and grounded in real observations.

Data Collection Methods

Measuring River Velocity

River velocity is the speed at which water flows in the channel. It is important to measure velocity because it influences erosion and sediment transport. Velocity can be measured using a flow meter or by timing a floating object over a set distance.

The flow meter is placed in the water at different points across the channel to get an average velocity. Alternatively, you can measure the time it takes for a floating object (like an orange or stick) to travel a known distance downstream.

Channel Cross-Section Surveys

This method involves measuring the shape and size of the river channel at a specific point. Using tape measures and ranging poles, you record the width and depth of the channel at regular intervals across the river. This helps to understand how the channel changes along the river course and how it affects flow and sediment transport.

Beach Profiling

Beach profiles show the shape of the beach from the backshore (near land) to the foreshore (near the sea). Using a ranging pole and clinometer or a simple slope meter, you measure the height and angle of the beach at regular intervals. This helps to identify features like berms, ridges, and troughs formed by wave action.

Sediment Size Sampling

Sediment size is measured to understand the energy of the environment and the processes acting on the coast or river. Larger sediment indicates stronger energy (e.g., stronger waves or faster river flow), while smaller sediment suggests weaker energy.

Samples are collected using sediment grids to randomly select stones or pebbles. These are then measured using a ruler or calipers to find the diameter. Sometimes sieves are used to separate sediment into size categories.

Using random or systematic sampling methods is important to avoid bias in sediment collection, ensuring the samples represent the area accurately.

For instance, if you collect 10 pebbles from a beach and measure their diameters, you can calculate the average sediment size to compare different parts of the beach.

Fieldwork Equipment and Techniques

Flow Meter Use

A flow meter measures water velocity by counting the rotations of a small propeller as water passes over it. It is held at various points across the river channel at about 60% depth to avoid surface turbulence and bed friction.

Multiple readings across the channel are averaged to find the mean velocity.

Tape Measures and Ranging Poles

Tape measures are used to measure distances such as river width or the length of a beach profile. Ranging poles mark points along a transect line or across the river channel to help take systematic measurements.

Sediment Grids and Sieves

A sediment grid is a frame divided into equal squares placed on the ground to randomly select sediment samples without bias. Sieves can be used to separate sediment into size classes for more detailed analysis.

GPS and Compass for Location

GPS devices help record the exact location of sampling points, ensuring data can be accurately mapped and repeated if needed. A compass is used to orient transects or measure directions of flow or sediment movement.

Safety and Ethical Considerations

Before fieldwork, a risk assessment must be carried out to identify hazards such as fast-flowing water, slippery rocks, or unstable cliffs. Appropriate safety gear like life jackets, sturdy footwear, and weatherproof clothing should be worn.

Minimising environmental impact is vital. Avoid damaging vegetation (e.g., trampling plants), disturbing wildlife (such as nesting birds), or leaving litter. Always seek permission and access rights from landowners or authorities before entering private or protected areas.

Weather and terrain can pose challenges. Fieldwork should be planned around tides, river levels, and forecast weather to avoid dangerous conditions. Terrain such as steep banks or rocky shores requires caution and sometimes specialist equipment.

Learning Example: Calculating Average River Velocity Using a Flow Meter

Suppose you measure river velocity at five points across a channel using a flow meter and get the following readings (in $\mathrm{m\,s^{-1}}$): 0.8, 1.0, 1.2, 0.9, 0.7.

To find the average velocity:

$$\text{Average velocity} = \frac{0.8 + 1.0 + 1.2 + 0.9 + 0.7}{5} = \frac{4.6}{5} = 0.92\,\mathrm{m\,s^{-1}}$$

This average velocity can then be used to estimate discharge or compare flow speeds at different points along the river.