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Geomorphological processes that are active in floodplain areas are related to terrain elevation. The rate of sedimentation, as well as the texture and the quality of the deposited sediments, depend on the frequency of flooding and the sedimentary conditions during flood events. In addition to geomorphological and soil maps, digital elevation models may provide a sound base for quantitative studies of these processes: flood hazard and, in the case that historical elevation data are available, sedimentation and erosion rates may be derived from the digital representation of relief over space. This paper discusses the interpolation techniques and the test procedures that were used to compute a digital elevation model of a part of the floodplain area of the River Geul (the Netherlands). It was found that the fitting of mathematical splines outperforms local averaging and inverse distance weighting for estimating floodplain elevation. By means of the Digital Elevation Model and a long profile of the river, a flood hazard map was constructed. Photographs of a flood event were used for validation. Analysis of variance revealed that 57-65 per cent of the variance in a set of data on flood-related topsoil metal content can be accounted for by the flood hazard map.

In many technological applications layered materials have an increasing importance. Almost complete characterization of such materials can be achieved with glancing incidence x-ray analysis (GIXA). Within this technique, x-ray reflectivity and angle-dependent x-ray fluorescence measurements are combined, resulting in a structural and chemical analysis of the samples.

Glancing-incidence x-rays provide a wealth of possibilities for the analysis of thin layers and multilayers. This paper discusses reflectometry under both specular and non-specular conditions, and also the combination with angle-dependent x-ray fluorescence. From these measurements information can be obtained on layer thickness, interface quality and compositional depth profile. First the historical development of glancing-incidence x-ray analysis is sketched. Then the physical principles of the interaction of glancing-incidence x-rays with samples which may contain rough interfaces are discussed. The equipment, which allows for both x-ray fluorescence and reflectivity measurements, is also described. The possibilities are illustrated with a number of examples from the literature.

The accuracy of Fundamental Parameter-based XRF quantification is investigated for both bulk and multilayer analysis. It is found that for bulk materials the relative accuracy is of the order of 1% and for multilayers a few percent. The method can be set up in such a way that it contains an inherent validity check. Further possibilities of the Fundamental Parameter method are discussed.

The co-regionalization between relative elevation and zinc concentration was used to map zinc concentration in the soil of the Geul floodplain in the southern Netherlands by co-kriging from 154 observations. Point co-kriging and point kriging for estimating zinc content in the soil were compared in terms of kriging variances. Another 45 samples were used to compare the precision of the estimated values in terms of squared and absolute estimation errors. Point co-kriging produced better estimates of zinc concentration than either simple point kriging or linear regression from the relative elevation data alone. Moreover, the estimation variances for co-kriging are substantially smaller than those for kriging. The results suggest that knowledge of geomorphological processes can often improve the quality of interpolation maps of properties that are expensive to measure.

For a specific flood on the polluted River Geul in March 1988, the relationships between river discharge, sediment concentration, and associated metal levels have been investigated. It was found that river discharge has only a limited influence on the transport of sediment and Pb, Zn, and Cd. During flood peaks its role is prominent, but at the intermediate stages between peaks, the quantity and quality of transported sediment depend on the variable activity of various sediment sources upstream. Nevertheless, when data from more floods are assembled, sediment and metal rating curves are obtained, which provide correlation coefficients of 0-63-0-92. Using these curves, mass transport calculations were carried out which demonstrate that the bulk of the annual transport of sediments and heavy metals occurs during a limited number of major floods.