Measuring beach slope angleYou are here: Home >> Coast >> Low energy coasts >> Stage 2

Stage 2: Fieldwork

When and where to carry out your fieldwork

Fieldwork on the beach may take you several hours to complete. To ensure that you have enough time, try to carry out fieldwork on a falling tide, starting ideally 1-2 hours before low tide. A larger amount of beach is exposed on a low spring tide that a low neap tide. Use this page to choose the nearest location to the beach where you are sampling. Pick out the low water predictions (L) with the lowest heights above chart datum.

Transects

For investigations along the shoreline, choose regular intervals along the beach. At each interval, take a vertical transect from the sea shore up to at least the high-tide mark. Use a tape measure or ranging poles to ensure that you keep to a straight line.

At 2m intervals up the beach, place a quadrat on the surface, and use this to select 10 stones from the surface. Measure the shape and size of each stone. Where there are no pebbles, use a trowel to take sediment samples from the surface. Each sample needs to be dried in the lab, then broken down with a pestle and mortar. Find the total mass of the sample. Then shake through a series of sieves, each decreasing in mesh size. Find the mass of material at each level.

Measure the profile of the beach at each interval.

Pebbles on a beachPebble measurement

(a) Simple methods

The simplest way to measure pebble shape is to classify the stone as very angular, angular, sub-angular, sub-rounded, rounded or very rounded. Decide which shape is the best fit for each pebble.

very angular
angular
sub-angular
sub-rounded
rounded
very rounded

For an estimate of pebble size, measure the longest axis of each pebble.

(b) More complex methods

3d pebble

For more precise shape data, use Cailleux's Flatness Index to measure the degree of roundness. The raw data needed for each pebble is as follows.

  1. The length of the longest axis (called l)
  2. The radius of the sharpest angle (called r)

To calculate the Cailleux Index see Stage 4.

For more precise size data, measure the a, b and c axes of each pebble. For pebbles where it is difficult to pick out the axes, allow the pebble to rest on a flat surface. The length of the longest axis is the a axis.

The a, b and c axes can also be used to calculate Krumbein's Index of Sphericity and for Zingg's shape classes (see Stage 4).

Beach profiles

Using ranging polesTo measure the angle of a slope between two points you need two or three people.

Identify a slope unit between two breaks of slope. Measure this distance.

Person A stands at the bottom of the slope with the clinometer resting on top of a ranging pole.

Person B holds a second ranging pole at the top of the slope.

Person A sights the clinometer at the top of the ranging pole held by B and reads off the slope angle.

Angles going uphill are recorded as positive (+) angles and downhill as negative (-) ones. Measuring the angle of a slope at regular intervals is more straightforward, but it tends to hide the small variations in slope which can be important on a beach.

Measuring from break of slope to break of slope means that you have to estimate where the slope angles change. This means that you normally end up taking more slope readings, but the profile that you draw is more accurate.

GO TO NEXT STAGE: Finding more data

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