Sediment fillings in valleys of the Ruhr area resulting from human impact in different periods of history

Abstract

Sediment fillings in valleys of the Ruhr area resulting from human impact in different periods of history. This paper deals with the Holocene sediment filling in the Kalwes Valley, a small valley in Bochum, which lies in the southern Ruhr area of Germany. The Kalwesbach catchment was affected by humans from the Neolithic period. Coal mining occurred at different phases until the 1960s, when the Ruhr-University was built on the loess-plateau surrounding the valley. Since that time rainwater from sealed surfaces has been fed into the Kalwes Valley via several drain inlets. It has been possible to differentiate the valley fill into four different strata. Overlying two periglacial layers, a stratum of humous and silty alluvia has been found that forms the major part of the sediment filling. 14C-analysis of wood fragments found in these “floodplain fines” suggests that accumulation began in modern times. The “floodplain fines” contain heterogeneously distributed hard coal particles of extremely high content in some thin layers. Coal content has been quantified by density separation in heavy liquid. The sedimentary depth containing the most coal was dated to the 18 th or 19 th century by 14C-analysis. Hence, coal particles seem to derive from early coal mining in small open pits near the banks. Only in a certain reach of the valley bottom has another layer of up to 1 m in thickness been detected covering the “floodplain fines”. The very coarse-grained material with a more than 60 % content of gravel and stones derives from a small tributary where excessive erosion has been caused by direct runoff from the university area since the 1960s.