Downsforce Project - landscape evidence

Slit trenches

There were no hardened field defences constructed on the Downs; it was a matter of digging in and so Downsforce's static positions comprised earthworks; slit trenches, breastworks and dugouts.

A typical trench is shown at right; this is one of the better examples, retaining part of its corrugated iron revetment. This one trench provided a lot of useful construction data as to the method of arranging the iron.

Identifying slit trenches

However, many slit trenches were filled in during the war to stop redundant positions being used by the enemy in the event of invasion. The Army was supposed to have filled in the remainder after the war as part of the cleaning up process, but a large number appear to have escaped their attention. This was probably to focus on the more urgent need to sweep the area clear of unexploded ordnance and return the Downs to a safe public area.

This oversight is good for me as it makes trenches easy to identify - even those partially filled in often retain evidence of angle-iron pickets in the corners, but what about those trenches completely filled in with all traces of ironwork removed?

This is where some detective work comes in; I'm not an archaeologist so I have no access to geophysics equipment or the like and rely on empirical data to identify a trench.

Seeing with the eyes is sometimes not enough; I've found seeing with my feet a useful technique as shown at left.

In cases where what might be a trench is not easily identifiable from a natural dip in the ground, slowly moving your feet along the perceived edge of the trench can help establish if both edges are almost uniform and if the feature is 'dish-shaped' as described by the red line and angle of my feet.

Marking the area with a tape measure pegged to the standard trench size (180cm x 60cm, with variations) can help and makes it easier to photograph the position.

Other techniques I've found useful are to see if the 'trench' is in a position where it can cover the ground and if it fits in with known trenches in the area. The orientation can also aid identification; a series of these features aligned at perhaps 60°, 90° or 100° (or other round number) would appear to be a deliberate alignment and not a natural formation.

In a landscape that has been used by man and animals for thousands of years I'm always wary of declaring an unidentified feature as a trench without a good combination of identifiying factors. At least two visits on seperate occasions, if possible in different conditions (low winter vegetation is essential), can tip the balance either way. This combination of techniques has helped me be more confident in recording possible features as trenches and also rule out others.

Recording and mapping

The large number of trenches in close proximity make it hard to distinguish each as an individual work, let alone its role in the wider scheme of section, platoon and company localities. Mapping (in a very broad sense of the term) has therefore been essential in interpreting the layout of the defences.

The graphic at right shows a digitised sketch map I drew in the field. These sketches are vital in trying to identify trenches and how they fit into the landscape.

The sketch shows four basic groups of trenches; the distance between each of the groups is not in proportion but the trenches within each group do give an impression of their layout.

Having identified features and marked their location with GPS, I begin charting them by measuring distance and bearing between them and notable landmarks such as trees to create a "semi-accurate" map. I say "semi-accurate" as I have no access to proper surveying tools, so my method of triangulation is rather haphazard!

The 20 trenches seen above were the first that I found and as I wasn't expecting to find many more, I carefully recorded their positions with my tape measure and compass. However, after the documents began targeting more areas and the number of trenches rocketed to 50, then 80, then 100 and to 337 (where it currently stands) I decided to use my GPS receiver to do the surveying instead; this is as technical as my fieldwork gets.

The problem with GPS is that there is a limit to its accuracy; my device (seen at left) constantly tells me how (in)accurate it is, depending on its ability to pick up signals from satellites. I can usually get an error margin of 10m, although I hope to get it down to 5m in most places; 4m is the best I've ever registered.

5m accuracy is never normally a problem except when you come to multiple features that might be only a few metres apart, as they become indistinguishable when so close and with a GPS inaccuracy. So while you can stand at the corner of one trench and use GPS to calculate the distance and bearing to other trenches, the data will never be 100% correct. However, I'm happy to have a few metres lost/gained here and there with the resultant inaccuracy for the time it saves using the tape measure and compass.

The main purpose is to produce maps that enable me to walk the ground in future and be able to see the trench arrangement in the landscape; it's actually very easy to view one locality of 5-6 trenches, and by the time you've walked to the next locality's trenches, you've lost track of the first group because you can no longer see them. Look again at the sketch map above; the six trenches at top right should actually be rotated 90° to the left; it's just that when I was sketching these localities, this is how the layout seemed.

The excitement of discovery and the fact that a new trench appears every 5-10m means that an initial sketch is all that's needed to get an impression of what's going on. Using the sketch in conjunction with the GPS data I then start creating my 'map' in Google Sketchup. An extract is shown below, with the field sketch to compare it with.

Verifying and evaluating the evidence

The process does not stop once a group of trenches has been mapped; there is still a lot more evidence to be extracted. The next stage is to take the map out into the field and check that it is accurate to the eye. This is a simple process that involves standing by each trench with the map aligned by the compass, and checking that the layout of trenches on the map follows that on the ground. Errors are noted and new data taken to correct them.

The map, however, is only 2-dimensional and to study the real layout, you need to be in the landscape to factor in the contours and different heights of the trench lines.

Once you realise that a higher line of trenches is sited so that it can't shoot directly into a forward line further down the slope you begin to see the defence of the landscape in action; the layout of trenches also allows an analysis of their fields of fire to be made.

The image at right shows six trenches (probably a section locality) laid out in Google Earth.

Mouse over the image to see the fields of fire highlighted.

Note how the trenches are arranged for all-round defence; each section could defend itself from attack in any direction, as could a platoon or company.

There are subtle contour changes that Google Earth cannot reproduce, but the upper two trenches are set slightly higher up the slope but can still cover the rest of the position.

The main purpose of this section was to cover the sheep track and slope above it and only the top left trench cannot cover this area without risking shooting into one of the other trenches. However, it is usefully employed covering the rear and a gap on the flank between it and the neighbouring section locality.