As the excavations have got underway and continued in earnest this week at Blelham Tarn, I have been there for several days in both sunshine and occasional heavy downpours undertaking detailed topographic survey of the site. When the survey is eventually drawn up it will complement both the excavations and geophysical survey results and will give us a really detailed picture of this complicated site.
Two days were spent investigating the field containing the bloomery mound(s), using survey flags to differentiate the edges of breaks of slope to each earthwork, and then recording them using either theodolite or total station. The rough survey data has been overlain onto contour data at 10cm intervals that was created using LiDAR data, in order to give the general natural topography surrounding the site. One day was spent recording a large dammed pond and water channel located on the hillside above the bloomery and a further day was spent doing basic walkover survey to identify sites in the wider landscape surrounding the bloomery field.
The rough survey results still need to be drawn up in the field to create detailed hatchured plans of the archaeological features. Initial results have revealed that the core of the site consists of a small sub-rectangular building platform with a flattened slag mound to the west. The gap between these mounds is a relatively flat platform and would have been used as a working area, and it contains the two furnaces identified during the geophysical survey (location of magnetometry grid shown in orange). The first excavation trench (open trenches shown in pink) is located on the inner edge of this building platform and is set across a wheel pit that would have once held at least one water wheel to be used to power the bellows on one of the two furnaces.
There is a flat triangular working area located south of the bloomery which extends out into a bog. There is slight earthwork evidence for small dumps of slag/spoil on the area, and possibly the eastern edge of some type of building foundation (shown in the geophysics results). Two trenches will be opened in this area to investigate these features, as well as another trench which has been opened to record the tailrace running away from the wheel pit. There is no surface evidence for the tailrace as it was infilled with slag, although this is picked out beautifully on the geophysics results.
Upslope to the north of the bloomery there is a slight gully or remnants of a field boundary (not a headrace to the wheelpit) which has a further small slag heap set against it. On the steep slope above the site there is a large dammed pond with an overflow channel on the west side. It is probable that the pond was once used to power the waterwheel at the bloomery site but there is no direct evidence for this. The pond was heavily modified with a new dam in the Victorian era when it was used for hunting purposes.