QUANTITATIVE SEDIMENT SOURCE ASCRIPTION USING MAGNETIC MEASUREMENTS IN A RESERVOIR-CATCHMENT SYSTEM NEAR NIJAR, SE SPAIN

The magnetic properties of sediments from a dried-out reservoir and its inflowing streams were measured to provide a basis for sediment source determination. Quantitative estimates of source component proportions in the reservoir sediments were made using linear programming procedures. The study confirms that this type of research must be based on a detailed knowledge of the relationship between magnetic properties and particle size in both the sediments and the potential sources. In the case of the site studied, the Isabel II reservoir, near Nijar, S.E. Spain, the sediments generated by contemporary surface processes within the reservoir catchment fail to reflect fully the 19th century material largely responsible for the rapid infill of the reservoir. An additional source type, namely unweathered schist-derived material not represented in the fine sediments sampled within channels upstream from the reservoir, has to be included in the model before calculations of source component contributions can be made. It is inferred that one or more high magnitude, low frequency event outside the amplitude of the most recently operating processes was largely responsible for the infilling of the reservoir.