Metallurgic slag as a tracer in floodplain evolution studies

The aim of this study was to estimate sedimentation rates in floodplains and to investigate lateral channel migrations over the last centuries. Considering the difficulties in determining these parameters using traditional dating methods, we have used different kinds of slag rejected from former metal works. In the Ardenne region (southern part of Belgium), at the end of 14th century, iron factories moved near to rivers in order to take advantage of the hydraulic energy. At the same time, large quantities of slag produced in primitive blast furnaces were piled onto the floodplains, often very close to rivers. Consequently, microslag could be carried away either during floods or by lateral erosion to be deposited on the floodplains downstream. In order to use slag as a stratigraphical tracer, we located slag waste sites along rivers and we dated the periods of furnace activity from historical studies. Afterwards, we measured slag concentrations in the alluvium and we studied their evolutions in different borings. These results allowed us to reconstruct the appearance of the floodplain at the inception of the metal works and to estimate lateral channel mobility over several centuries. Moreover, different kind of tephra and 14C dating have been used in order to date the deposits that have been established before the settlement of metallurgy.