Comparing different shallow geophysical methods in a tidal estuary, Verdronken Land van Saeftinge, Western Scheldt, the Netherlands

Abstract

In order to validate existing models of sedimentation in active sedimentary environments, detailed stratigraphic information is indispensable. Near-surface geophysical methods provide a means to acquire high-resolution images of the stratigraphic succession in the shallow subsurface. Land-based and marine methods have been tested in the Verdronken Land van Saeftinge. This intertidal flat area is cut by numerous tidal gullies, and high tidal amplitudes enable the application of different techniques at various water levels. Data acquisition focused on the upper 10 – 20 m of the active sediment bodies. Applied techniques include high-resolution seismic acquisition, geo-electrical methods (DC resistivity), electromagnetic techniques, CPT, and manual drilling. In general the acoustic methods allowed more reliable and detailed interpretation of the sedimentary structures than the electric/electromagnetic methods. The latter suffered from the effect of tidal action and salt-water intrusion, and their application on land proved very strenuous. CPT and shallow cores provided valuable ground-truth information. The results clearly indicate that no single technique can provide all the answers. Only an integrated use of (complementary) methods will allow getting a better grip on the sedimentary architecture and preservation potential in active estuarine sedimentary environments.

Massive marine methane emissions from near-shore shallow coastal areas

“…In the Scheldt estuary, an increase of CH 4 was observed in the lower estuary (salinity >25) compared to the mid estuary (salinity ~15) (Fig. 2) which has been attributed to the presence of extensive tidal flats7, where gassy sediments also occur27. Hence, CH 4 seepage from shallow gassy sediments could be the main reason for elevated CH 4 concentrations in surface waters of both the nearshore BCZ and lower Scheldt.…”

Exploring Integrated Geophysics and Geotechnics as a Paleolandscape Reconstruction Tool: Archaeological Prospection of (Prehistoric) Sites Buried Deeply below the Scheldt Polders (NW Belgium)

“…Because of high groundwater saturation in polders, low attenuation of the seismic waves was expected, allowing a good resolution of shallow targets (e.g. Ghose et al, ; Missiaen et al, ). S‐waves are not affected by the fluid content of the sediments and essentially respond to the lithologic contrast (Johnson and Clark, ).…”

“…Therefore, the approach suggested by Vos () to identify peat merely from the friction ratio was adapted in our study (e.g. Missiaen et al, ).…”

Archaeological prospection of the nearshore and intertidal area using ultra‐high resolution marine acoustic techniques: Results from a test study on the Belgian coast at Ostend‐Raversijde

“…The last decade has seen a significant development in very high resolution seismic acquisition in shallow water environments (e.g., Baradello & Carcione, ; Missiaen et al., ; Wunderlich, Wendt, & Müller, ). Careful attention with regard to source and receiver, geometrical arrangement, and operational conditions is crucial to obtain accurate images of the shallow subsurface (Missiaen, ).…”

“…Different features, for instance hard layers or fine‐grained deposits, may sometimes yield a similar reflectivity and can therefore be easily mistaken (Stevenson et al., ). Integrated use of complementary methods is often needed to provide optimal information on sedimentary architecture and buried features, as shown by an extensive geophysical study in The Netherlands at Verdronken Land van Saeftinge, an intertidal marsh area in the Westerschelde estuary (Missiaen, Slob, & Donselaar, ).…”