Resistivity Survey at Red Dragon, Givenchy. Carried out by Dr. Iain Banks (Director, Glasgow University Archaeological Research Division) and Dr. Tony Pollard (Director, Centre for Battlefield Archaeology, Glasgow University).
In April 2006, a resistivity survey was carried out in a field at Givenchy-Lez-La Bassée in the vicinity of the Red Dragon crater, the result of a German mine that was exploded at 2.50am on 22 June 1916, causing much surface and underground damage. The intention of the survey was to detect any traces of the British tunnel that was damaged by the explosion, trapping a party of British tunnellers that included Sapper William Hackett VC of 254 Tunnelling Company and Private Thomas Collins of 14th Welsh Regiment (Swansea Pals).
The survey was a part of a larger potential project to excavate the remains of the trenches and tunnels at Givenchy-Lez-La Bassée, identify the location of the shaft near which Sapper William Hackett VC and Private Thomas Collins still lie 12 metres beneath No Man’s Land, and to erect a monument to the Tunnelling Companies of the First World War, a Corps whose endeavours have until recently been largely neglected by historians (Barton et al 2004).
When the Red Dragon explosion happened Hackett and Collins were part of a five-man team working in a tunnel running beneath the British trenches towards the German lines. The mine’s shock-wave caused considerable damage, bringing down 8 metres of gallery behind the tunnellers and thus cutting off their sole exit route. A rescue party was able to reach the gallery via the single access shaft – the Shaftesbury Shaft – and after two days of digging managed to extract three men. Thomas Collins, however, had suffered several broken ribs and was too badly injured to negotiate the narrow escape hole.
William Hackett, an experienced coal miner well-knew the danger of further collapse, yet insisted on staying with his comrade until access was possible that could extricate both men. Food was passed through and stabilisation work continued until another major roof-fall once more entombed the two men. Despite four more days of digging, it was found impossible to regain contact; in addition, the shaft itself was suffering from the effects of incessant hostile shelling and mortaring; it too was at risk of collapse, endangering the lives of the rescue party themselves. Eventually, efforts had to be suspended. The bodies of William Hackett and Thomas Collins were never recovered and still lie in the tunnel to this day. The intention of the survey was to locate elements of the WW1 trench system, any indication of the entrance to Shaftesbury shaft and signs of the Givenchy south crater field, an area long reclaimed by agriculture to the point where only a shallow depression on the site of the backfilled Red Dragon crater is now visible to the naked eye.
The survey consisted of a resistivity survey carried out over 20m grid squares in a field beside the main road through the village. Resistivity is an electrical technique that measures the resistance encountered by an electrical current passed through the soil between two pairs of probes. One set of probes is in a fixed position, while the other set is mounted on a frame and inserted into the ground at regular intervals. In the case of the survey undertaken here, the interval was 1m along traverses set 1 m apart. This meant that 400 readings were collected from each 20 m grid.
The readings recorded are a measurement of the amount of resistance encountered by the current as it passes through the soil. There will be minor variations in the amount of resistance irrespective of the presence or absence of archaeology. Archaeological features cause larger alterations in the resistance: backfilled features such as ditches, trenches, pits, craters etc. retain more moisture than surrounding undisturbed soils and therefore provide relatively low resistance as the moisture allows the current to pass more easily. Solid objects, such as walls, create a higher resistance. The results will show on a greyscale plot as dark or light patches.
The equipment used was a Geoscan RM15 resistivity meter, with the results downloaded and processed in Geoscan’s Geoplot v3 software. This allows the results to be filtered to remove background noise, largely consisting of the natural fluctuations in resistance that are present in all soils. The results are presented as a greyscale plot that consists of all the individual 20 m grids stitched together. In the event, 15 grids were surveyed, giving coverage of 6,000 m².
The fields were very dry when the survey was undertaken. There had been considerable rainfall in the previous weeks, but this had substantially evaporated by the time of the survey. This meant that the readings in the survey were uniformly low, representing the depleted levels of moisture present. This means that the results have to be treated with due caution because the variations between the readings is very small; it would thus be easy to misinterpret minor variations as major features. Equally, it is possible that major features would produce only very low anomalies.
The most obvious anomaly in the field is a very large circular entity (A; fig 2) in the right hand (south eastern) part of the plot. Although it is essentially circular, there is a break in the circumference on one side (north). There are also indications of variation across the interior of the anomaly. The essential characteristics of the readings in the anomaly suggest a ring of compacted soil surrounding looser material in the interior. This is what would be expected of a backfilled mine crater. The explosion would throw the soil upwards, and some would then fall back, partly re-filling the crater. The edge of the crater would be compacted by the shockwave, a force that would be in the process of dissipating by the time that the upflung soil was no longer falling. This would cause an area of compaction that would be quite narrow. The dimensions of the anomaly seem to be as might be expected of Red Dragon, being roughly 45 m in diameter: the precise dimensions are difficult to determine as it is the physical effects of the blast that have been measured. It is hard to find an alternative interpretation of the results. The break in the circle may be the result of later shelling or mine blasts; Red Dragon dates from June 1916, while this area was continuously a part of the front line until the end of the war (Barton 2006, 1). It is likely that later actions will have had an effect on the geophysical properties of the soil.
There are further anomalies within the circumference of the anomaly representing the mine crater. These may represent later uses of the crater, again adding to the palimpsest of the resistance patterning across the field. Excavation would clarify whether these do represent later elements of the trench system or whether they are artefacts of the overall pattern of resistance from the crater.
One of the other significant elements of the geophysical results relates to a linear anomaly that runs roughly along the line of the field edge (B). This initially looked as though it would merely represent the difference between the two fields; one was ploughed and harrowed, while the other bore a crop and was relatively compacted. The difference between the fields is readily apparent in the parallel stripes running at a slight angle down the smaller field: indications of ploughing that are absent from the larger field. The linear anomaly is certainly partially represented by the field edge, but there is more to it than that. The anomaly appears to run through the crater, but there is a right-angled bend to it at the crater ‘lip’. At this point, it runs for roughly 20 m to the NE, and then cuts back to the SE. This makes the anomaly appear to avoid the anomaly of the crater. The top end of the anomaly, furthest away from Red Dragon, has a stronger anomaly (C) that creates an irregular, sub-circular pattern of higher resistance. It is a rather jumbled patch of readings, but the tendency is that the readings at this point are higher than the surrounding soils in either field. There is also a second, rather faint line that runs across one corner of the plot (D). This may be created by the presence of patches of lower resistance, but it does seem to snake across the ground past Red Dragon. The final element of note is visible in the lower contrast plot (fig. 3). This consists of a small rectilineal anomaly that may have a larger rectangle enclosing it (E).
There can be little doubt that Anomaly A represents the Red Dragon crater, as the comparison to the map and aerial photograph indicate. The stronger linear anomaly (B) represents a trench which may be that which appears as a dotted line on the trench map to the west of the crater, though as previously stated, it is likely that at least part of the anomaly derives in particular from the field boundary. However, the fact that the anomaly appears to turn away and then back would suggest that the field boundary is not the entire explanation and that this is also part of a British trench. The physical form of the anomaly also suggests that while there is a certain amount of higher (in the plot, darker) resistance as would be expected from a field boundary, there are parallel, lower readings that suggest a backfilled feature such as a trench or a ditch.
If Anomaly B is accepted as being the trench, it would have run into the crater, and would have been the trench occupied by the Royal Welsh Fusiliers on 22/23 June 1916. The deviation in the line, which would have been quite normal for a trench (to reduce the lines of sight along the trench in the case of enemy intrusion) may have been the restoration of the trench after Red Dragon had been blown; this remained the British front line despite the blast, and would do so until 1918.
The next anomaly (C) is probably another crater, in this case a smaller one that appears on the AP. It is likely to be a shellhole or small mine crater. The snaking faint line (D) may represent a second trench line that, according to the contemporary trench map, ran at an angle on the western side of Red Dragon crater. Caution is needed here because the map seems to be rather representational at times in its depiction (when compared to the aerial photograph). Nonetheless it does appear to correspond to the long angle of the triangular trench system which shows so clearly on the aerial photograph.
The anomaly at (E) may represent the top of a shaft, its location fitting well with the location shown on the map (Duck’s Bill No. 2) and in relation to the triangular shaped trench feature. It appears relatively geometric, which is generally a good indication that the anomaly is anthropogenic. It lies close to the edge of the crater.
As ever with geophysical survey, a note of caution must be sounded over the interpretations. The anomalies represent variations in the readings recorded by the resistivity meter. They may be the variations in the strength of the resistivity in the soil caused by the actions of the First World War, but they could also be purely the result of surface soil conditions. In terms of the conditions of the survey, the results were uniformly low, with a very small range in the readings. It would be easy in the circumstances to see features that are not real. However, on the basis of the survey, these interpretations are the best fit for the readings, and there is nothing else that can be suggested as representing the WWI features.