Assessing Dunes

Sand dunes are fun to explore.  There are lots of ups and downs and little paths to follow and being just behind the beach, they are a good place to find shelter on a windy day.

However, sand dunes are a vulnerable environment that is easily disturbed.  Strong winds from the beach readily move the loose sand around, blowing it further inland and rearranging the dunes, covering whole plants in one place and exposing the roots in another.

As we go tramping around our feet kick the sand about.  The plant roots cling on to the sand as best they can, but it is easy to disturb everything just a little too much.

Let’s investigate:

  • Is there more evidence of people just behind the beach or further inland?
  • Does the impact decrease as you get further away from the car park?

To assess the impact on the dunes you need a chart:

This is a basic outline, but you can add more rows and more things to investigate.

You need a copy of the chart for each site that you are going to assess.  You’ll need to visit 3 or 4 sites, at different distances from the sea, or different distances from the car park. You could pace out the distance between them.

At each site look around you.  Then put one tick on each row of your chart.  So with the first row, if it is really noisy then put a tick under -2; if it is really quiet then tick +2.  If it is somewhere in between – well you have 3 options.  Do each row in the same way.

When you’ve finished work out the total score for each site.  The best site, with the least evidence of people, will have the most positive score overall.  The worst site will probably have a negative total score.

You can adapt your chart to other situations too, by changing the descriptions at the ends of the rows.  Just keep all the bad stuff on the left and all the good stuff on the right.

Which is the best beach?  The best footpath?  The best village?

Use Your Quadrat

A quadrat can be used in all sorts of ways and you might find it useful for biology fieldwork too.  Here are some ideas for the beach.

Last week we found out how to use the quadrat to estimate percentages, so now try that with beach material.

What are the percentages of seaweed and sand?

Or the percentages of sand and pebbles?

If you are measuring pebble sizes then you can use the quadrat to tell you which pebbles to measure.

You could measure the pebble underneath each point where the strings cross…

…or if they are bigger you could just take one from under each of the corner junctions.  It doesn’t matter how you do it, as long as you decide the rules before you throw the quadrat down.

Sometimes, behind the beach you find sand dunes.

If so, then take your quadrat into the dunes.  Measure the percentage vegetation cover, just like I showed you last week with my patio weeds.

Does the percentage change as you get further from the sea?

Now look at the plants in detail.  Use a book or the internet to identify the different types.  At each location see which species covers the largest area.

Does the main vegetation type change as you get further from the sea?

If you want an easier option than identifying plants, count the number of different species in your quadrat.  You don’t need to know what they are.

Does the number of plant species change as you get further from the sea?

We’ll look at dunes again next week – there are a few more things you can investigate, that don’t involve quadrats.

Make a Quadrat

There are plenty more beach fieldwork options to come, but first you need to make yourself another piece of equipment – a quadrat.

To make one of these you need something to make the outside frame and then string to divide the central area into smaller squares.  You also need a tape measure to help you get everything in the right place.

For the frame I used garden canes, but lengths of wood would work too and would probably be more robust.  You need to cut 4 lengths of about 60 cm.  The inside edge of the frame will be 50 cm x 50 cm, but you need the extra length to fix them together.

Use string to lash the frame together at the 4 corners.  (Lengths of wood could be screwed together.)

Make sure the internal area of the square is exactly 50 cm by 50 cm.

You are going to divide the frame every 10 cm.  Mark the edge with permanent marker so that you know where to fix the strings, and so that you can see where they should be, if they slip out of position.  There should be marks at 10, 20, 30 and 40 cm on each side.

Now tie strings across.  Go first one way…

…and then the other way, twisting around each of the first set as you go.

Check the squares are still square (10 cm by 10 cm) and adjust if necessary.

And there you have it…

…a very useful piece of kit.

Here’s one way to use it.

As you can see my patio needs weeding!  We can use the quadrat to help us estimate the percentage of my patio that is covered in weeds.

Throw the quadrat down.  Yes, don’t place it, since that would be you choosing the results.

The quadrat has 25 small squares so each of them represents 4%.  Give each square a score:

  • Square is all weeds = 4
  • Square is ¾ weeds = 3
  • Square is ½ weeds = 2
  • Square is ¼ weeds = 1
  • Square has no weeds = 0

Add them up and you can see that 45% of my patio is covered in weeds.

I’m off to do some gardening, but I’ll be back next week to tell you how to use your quadrat at the beach.

 

Hold on to that Beach

Seaside resorts would lose their popularity and their customers if they lost their beach.

Where the local council want to be sure to keep, and even build up their beach, groynes are often built – those wooden fences that point straight out to sea and can make a walk along the beach something of an obstacle course.

Groynes also provide a handy indicator of the predominant direction of the longshore drift.  The beach material piles higher, and the waves don’t come in so far, on the side that has the most longshore drift moving towards it.

You can see the effect on this satellite view of Bournemouth.

So if your beach has groynes, then you need to go armed with a tape measure.

Measure from the top of the groyne vertically down to the beach material.  Do two measurements at the same place, one on each side of the groyne.  You’ll get a smaller measurement where there is a bigger pile of beach material and that’s the side that the longshore drift is coming towards most of the time.

Here are some things to investigate:

  • Is the height difference bigger closer to the sea?
  • Is the height difference bigger at one end of the beach?
  • Is the longshore drift for a particular day (as shown by a float or pebbles) the same as the overall longshore drift direction (shown by the groynes)?

And don’t forget to check out the satellite view of your favourite resort.

Drifting Pebbles

Last week we learnt about longshore drift, and a simple method for finding out its direction on the day of your fieldtrip.

Longshore drift constantly shuffles beach material.

This is Chesil Beach in Dorset.

The beach material is clearly sorted, from small size at the west end…

…to large size at the east end.

(Zoom in on the photos to compare them – if I crop them any more you will lose the sense of scale.)

Longshore drift is usually from west to east on this part of our coast, as the most powerful waves tend to come from the south-west, causing all the beach material to move eastwards.  Less frequently the swash comes from the other direction, and longshore drift goes east to west, but waves from this direction are usually less powerful – only the smaller pebbles get shifted back to the west again.

Here’s another method for looking at longshore drift but this one needs a bit of preparation.  You will need to collect some pebbles, preferably a variety of different sizes, and paint them in a bright colour.  (Don’t use water soluble paint!)

At the beach, put your painted pebbles into the water, all at the same place.  Best to do this as the tide is coming in.  Otherwise they may not move very much before being left high and dry.  Leave them as long as you like, the longer the better.  Just make sure that you know where they started from.  Hopefully you will be able to find some of them at the end of your experiment.

  • Did they move along the beach?
  • Did they all move in the same direction along the beach?
  • Which moved further, bigger or smaller?