Radar facies of unconsolidated sediments in The Netherlands : A radar stratigraphy interpretation method for hydrogeology

Since 1990, The Netherlands Institute of Applied Geoscience TNO has been carrying out ground penetrating radar (GPR) measurements to assess the potential for imaging and characterising different hydrogeological targets in more than 30 pilot areas in The Netherlands. The experience gained by processing this large amount of radar data has enabled reflection patterns characteristic of different depositional sedimentary environments to be identified. This paper presents typical examples of radar patterns for almost all the sedimentary environments in The Netherlands which are suitable for GPR measurements, including glacial (push moraines, glacio-fluvial deposits, glacio-lacustrine deposits), aeolian (coastal sand dunes, river dunes, cover sands), fluvial (braided river systems, meandering river systems), lacustrine (fen pools) and marine (beach ridges, estuarine deposits, littoral facies). Listing the different radar facies elements characteristic of each environment forms an aid for identifying the types of sedimentary sequences. This radar stratigraphy procedure will be helpful when defining the hydrogeological setting of the subsurface. Aquifer imaging is completed by characterising the reflections from the water table in the various environments as well as the reflection patterns from the host rock, because the intensity of a water-table reflection largely depends on grain size. The most characteristic parts of the GPR sections representative of the different sedimentary environments of The Netherlands have been grouped into a synoptic 'radar facies atlas', together with the inferred reflection patterns

Ground penetrating radar images of selected fluvial deposits in the Netherlands.

Ground penetrating radar (GPR) surveys have been carried out in order to characterise reflection patterns and to assess the method's potential for imaging palaeofluvial sediments in the Mass-Rhine former confluence area in the southern Netherlands. The results show that the deposits of meandering, braided and transitional river types produce characteristic radar facies. Representative examples of each of these river types were selected where the GPR data could be directly correlated with sedimentary information derived from exposures and detailed drilling, and geomorphological data could be supplied. Individual channels may be distinguished by the radar facies of their fills. The floodplains of the different river types also show a characteristic radar facies. In GPR data from the meander floodplain, parallel, dipping reflections represent point-bar structures, while irregular, intersecting small channel patterns that alternate with parallel continuous reflections are more typical in the braid plain. A transitional river type shows characteristics of both of these types. Typical examples of GPR sections recorded in each of the different fluvial palaeoenvironments are presented in an interpretative radar facies chart

Ground penetrating radar for determining volumetric soil water content; results of comparative measurements at two test sites

Ground penetrating radar (GPR) can provide information on the soil water content of the unsaturated zone in sandy deposits via measurements from the surface, and so avoids drilling. Proof of this was found from measurements of radar wave velocities carried out ten times over 13 months at two test sites in the Netherlands. At these same locations and on the same dates, soil water content was measured in access robes using a capacitance probe. Comparison of GPR and capacitance probe observations revealed that: 1. The inferred absolute values of soil water content agree well. This is remarkable because the soil water content is deduced entirely differently for the two methods. 2. Seasonal fluctuations in soil water content established for different (general) depth zones of radar waves correlate well with the fluctuations observed in the access tubes. 3. The various methods to determine the propagation velocities of radar waves are complementary; together they produce a realistic and reasonably complete image of the vertical distribution of the soil water content of the entire unsaturated zone. High-frequency (200 MHz) direct groundwaves and refracted waves constitute a particularly attractive complementary combination, which provides information on consecutive shallow zones in the underground, i.e. the zones of major soil water content fluctuations. 4. Lateral variations established at one of the test sites where several access tubes have been placed in a transect also follow from the GPR measurements along that profile; this non-destructive determination of soil water content in practically continuous and detailed sections is one of the great assets of GPR, opening the way to mapping preferential soil water flow paths

Benthic Habitat Variations Over Tidal Ridges, North Sea, The Netherlands

Marine ecosystems on continental shelves endure an increasing burden of human activity offshore, and the impacts on benthic habitats are not well known. An improved understanding of how benthic habitats vary in relation to substrate types and seabed features is therefore essential to both scientists and offshore developers. This case study shows that marine habitats over two tidal ridges in the North Sea vary from low-density/low-diversity communities on the well-sorted sandy crests of ridges to high-density/high-diversity communities in the poorly sorted muddy, gravelly sediments in the adjacent troughs. On sandy continental shelves, including the Netherlands Continental Shelf (NCS) in the North Sea, tidal bedforms occur of different spatial scales, such as sand banks (tidal ridges), sand waves, and megaripples. Marine habitat maps reveal that benthic habitats vary spatially on continental shelves in relation to seabed morphology, water depth, and sediment composition. The different morphological elements of tidal ridges are expected to accommodate different benthic habitats. Some tidal ridge areas in the North Sea are nominated to become marine protected areas, but are also attractive for their marine aggregates and may be designated in part as mining areas. Due to their composition and shallow water depths, tidal ridges are also suitable locations for the construction of offshore wind farms. To date, the characteristics of relatively inaccessible seabeds are too poorly understood to explain the effects of physical parameters on benthic communities. Therefore, it is important to expand our understanding of benthic habitat variations associated with tidal ridges, for the benefit of both science and offshore development. © 2012 Elsevier Inc. All rights reserved