Abstract

Investigations on suspended sediment colour took place from 1998 to 2006 with daily stream water samples in the Olewiger Bach basin (Southwest Germany) and floodwater samples in in the Attert River basin (Grand Duchy of Luxembourg). Moreover, fine bed sediments, suspended sediments and potential suspended sediment sources were sampled during the course of one year in order to use the classical fingerprinting approach together with colour information to identify suspended sediment sources.

To estimate sediment colour, each sample was filtered through a fibre filter, scanned under a microscope with a digital camera and placed in an oven for 5 hours at 500 °C. After cooling and re-weighing, filters with the remaining inorganic particles were scanned again. The digitized colour values, which contain the red, green and blue colour information and the luminosity value for the residue, were stored using the common graphic format TIFF. An eight-bit resolution for each colour, that is a total colour depth of 24 bits, provides 256 x 256 x 256 = 16.8 x 106 colours. In contrast, the human eye can only differentiate 200,000 colours. Particle colour turned out to be a useful, fast and easy approach for examining variations in suspended particle characteristics even at very low concentrations. Results illustrate a high spatial and temporal variability of suspended particle characteristics during flood events. This variability was related to changes in the composition of suspended solids caused by the changing lithology of the variable source areas just like seasonal changes of hydrological and climatological conditions. During the winter season and more so during flood events sources located further from the streams were active. Contrarily, during summer low flow conditions, in-channel sources became more significant.

Keywords: particle colour, suspended sediment sources, sediment fingerprinting