|Measuring sediment properties in the field using MEDUSA RhoC|
Eelkema, M. (2008). Measuring sediment properties in the field using MEDUSA RhoC. MSc Thesis. Civil Engineering and Geosciences: Delft. xiii, 61 + appendices pp.
sediment · radioactivity · density · composition
A promising new method for measuring sediment properties in the field is called MEDUSA RhoC. This device measures mud and sand content, sediment density, and water content in the field using Radiometric Sedimentology. The aim of this thesis is to investigate the accuracy and applicability of the MEDUSA RhoC system with its new components. This is done by comparing results obtained with the RhoC to results obtained with traditional analyses, both in the lab and the field. Besides this, also the general characteristics of natural sediments are investigated in order to see what other properties can be derived from mud content, sediment density and water content alone.The radiometric activity of sediment is related to its mud content. The MEDUSA RhoC system determines mud content by measuring the radio-activity of sediment, and translating the activity to mud content. The relation between mud content and activity concentration is called the radiometric fingerprint. Depth averaged sediment density is determined by pushing a radio-active source into the soil, and measuring the attenuation of the activity coming from the source. The water content is determined with a technique known as Time Domain Reflectrometry.To investigate the performance of the RhoC under controlled circumstances, tests are performed in the laboratory and field. The field tests of the RhoC are performed on tidal flats in the Western Scheldt. On several locations in the Western Scheldt the RhoC is used to measure radiometric activity, density profile, and water content. At the same locations, sediment cores are collected. These samples are taken to the laboratory to determine sediment density, water content, grain size distribution, organic matter content, and radiometric activity concentration. This is done using "ordinary" techniques.The laboratory analyses on the sediment samples taken from the Western Scheldt show several relations between various sediment properties. The RhoC measures only the mud content, bulk density, and water content. From these properties other properties such as the silt content, clay content, porosity, and relative water content are derived. These properties are important for the mechanical behavior (such as erosion) of the sediment.In general, the MEDUSA RhoC system is able to supply valuable information on the composition, density, water content, and stratification of sediment. Although these properties are the only things the RhoC measures, the known relations between these properties and other parameters enable the user to derive much more qualities. This makes the MEDUSA RhoC system a valuable measuring device for sediment mapping, which can improve the quality of the input parameters for large-scale numerical models.