If there is a single large groyne or jetty, take pebble measurements and profile readings at frequent intervals on both sides of the groyne. If there is a series of groynes on a beach, take pebble masurements and profile readings on either side of each groyne and at distances in between. 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.
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.
For an estimate of pebble size, measure the longest axis of each 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.
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).
To 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.
The table below shows some examples for criteria you can use in a bi-polar survey. A pilot survey will show whether the criteria you have chosen are appropriate. This will also help you to judge what precisely you mean by, for example, 'ugly'.
|BIPOLAR EVALUATION OF SEA DEFENCES|
|NEGATIVE EVALUATION FACTOR||-3||-2||-1||1||2||3||POSITIVE EVALUATION FACTOR|
|Vulnerable to erosion (unable to 'hold the line')||Effective protection against erosion (able to 'hold the line')|
|Vulnerable to overtopping (unable to control flooding)||Effective against overtopping (good flood defence)|
|Ugly (poor aesthetic value)||Enhances natural environment (high aesthetic value)|
|Poor access to beach||Good provision made for access to beach|
|High risk safety hazard to general public||No obvious safety risk to general public|
|Short lifespan &/or high maintenance costs||Good life expectancy &/or low maintenance costs|
|High levels of disturbance caused to local people during construction||Low levels of disturbance caused to local people during construction|
|Disturbs natural coastal processes & habitats||Maintains natural coastal processes & habitats|
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