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Skip to 0 minutes and 11 secondsThere are many ways that you could estimate the area of land that is sealed in your local area. Here are just a few ideas. You could walk round the local area, focusing on a particular area and note how much land is sealed. I'm doing this for Lancaster University campus. To help me keep track and estimate the percentage of area that's sealed, I'm marking it on a map. You could also use a sketch map or take notes. Using a local map will tell you a lot about the land use. And if it's sufficiently detailed, you'll be able to work out whether it's sealed.

Skip to 0 minutes and 48 secondsI'm using a 1 to 25,000 ordinance survey map to identify areas which have buildings and those which don't. These maps are readily available in the UK and provide a very good source of information. Alternatively, you could use an online map if that's readily available. Depending on how accurate you want to make your estimate, you could print off the map and shade areas of sealing or do this in a computer programme, if you know how. Google Maps and Google Earth provide satellite images of many areas of the world.

Skip to 1 minute and 21 secondsBy looking over a given area, you could assess how much is covered by vegetation, and thus is less likely to be sealed, and how much is covered by buildings, roads, and other impermeable surfaces. There are special techniques available to do this sort of analysis. But we're just interested in an estimate. So you could zoom into the area you're looking at and estimate the area on your screen that looks as though it's sealed.

Practical activity - surface sealing

Soil erosion is only one of the threats to soils. Another threat is surface sealing.

Surface sealing is the covering of the soil surface with impervious materials. This mainly occurs as a result of urban development. Once an area is sealed it is lost to other land uses such as agriculture and normal soil functions are either severely impaired or prevented. There is a growing awareness of this problem in some regions of the world, especially in relation to flooding since water flow patterns are heavily impacted by surface sealing.

The majority of surface sealing can be seen in urban areas. Look around your local area and see if you can estimate the percentage of land that is sealed.

Watch the video for some ideas about how you might estimate surface sealing. Your estimate can be approximate or you can have a go at being more precise. If you need to refer to written instructions, you can use the transcript in the downloads section below.

Post the result in the discussion below together with the approach that you used.

  • Do you think surface sealing is a big concern where you conducted this exercise?

  • In Europe an average area of 200 m2 is sealed per person. Do you know to what extent surfaces are sealed where you live?

Safety tips

You will be walking around making observations.

  • Be aware of other people and potential hazards around you – roads, pavement kerb and uneven surfaces.
  • If you are in a rural area you may encounter hazards of a different nature.

Please also see our safety tips in the introduction.

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This video is from the free online course:

Soils: Introducing the World Beneath Our Feet

Lancaster University

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