Mw. Naegeli et al., GROUND-PENETRATING RADAR FOR ASSESSING SEDIMENT STRUCTURES IN THE HYPORHEIC ZONE OF A PREALPINE RIVER, Journal of the North American Benthological Society, 15(3), 1996, pp. 353-366
Ground penetrating radar (GPR) was used to investigate the structure o
f the sediments in a floodprone gravel-bed river. Measurements were ma
de on 2 gravel bars and in the adjacent channel. We buried a metallic
object to calibrate depth and to visualize changes in GPR-profiles tak
en before and after digging. In addition, along 2 GPR-profiles the str
ucture of the alluvial sediment of a gravel bar was visually verified
by digging a trench down to the groundwater table. The GPR method enab
les,ne to distinguish sedimentary units of different texture with a ve
rtical resolution of about 0.25 m. The investigation showed the depth
of the alluvial valley fill, and it revealed geomorphological features
such as lateral point bar accretion, fills of former pools, or open f
ramework textures. These structures form a complex 3-dimensional mosai
c of sediment patches. The GPR method also allowed us to document the
changes resulting from bed-moving floods, such as in the formation of
homogeneous gravel sheets during high magnitude floods. At some sites
we observed intercalations of coarse organic matter between adjacent s
edimentary units. Based on GPR data and the analysis of geomorphologic
al structures near the study site, we developed a diagrammatic model o
f the sediments of this site in the lower Necker Valley.