Identifying Changes in Sediment Texture along an Ephemeral Gravel-Bed Stream Using Electrical Resistivity Tomography 2D and 3D

Abstract

Differences in deposit geometry and texture with depth along ephemeral gravel-bed streams strongly reflect fluctuations in bedload which are due to environmental changes at the basin scale and to morphological channel adjustments. This study combines electrical resistivity tomography (ERT) with datasets from borehole logs to analyse the internal geometry of channel cross-sections in a gravel-bed ephemeral stream (southeast Spain). The survey was performed through longitudinal and transverse profiles in the upper channel stretch, of 14 to 30 m in length and 3 to 6 m in depth, approximately. ERT values were correlated with data on sediment texture as grain size distribution, effective grain sizes, sorting, and particle shape (Zingg’s classification). The alluvial channel-fills showed the superposition of four layers with uneven thickness and arrangement: (1) the softer rocky substrate (<1000 Ω.m); (2) a thicker intermediate layer (1000 to 2000 Ω.m); and (3) an upper set composed of coarse gravel and supported matrix, ranging above 2000 Ω.m, and a narrow subsurface layer, which is the most resistive (>5000 Ω.m), corresponding to the most recent armoured deposits (gravel and pebbles). The ERT results coupled with borehole data allowed for determining the horizontal and vertical behaviour of the materials in a 3D model, facilitating the layer identification.

Integrated Geophysical Methods for Shallow Aquifers Characterization and Modelling

“…Since the call for papers was announced in June 2019, a total of 11 manuscripts were received. After a rigorous review process, eight papers have been accepted for publication [1][2][3][4][5][6][7][8]. To gain a better insight into the essence of the Special Issue, we offer brief highlights of the published papers below.…”

“…The paper "Identifying Changes in Sediment Texture along an Ephemeral Gravel-Bed Stream Using Electrical Resistivity Tomography 2D and 3D" [4] combines the ERT technique with datasets from borehole logs to analyze the inner geometry of channel cross-sections in a gravel-bed ephemeral stream in southeast Spain. The ERT models were correlated with sediment texture data, such as grain size distribution, effective grain size, sorting, and particle shape (Zingg's classification), in order to integrate the horizontal and vertical ER distributions into a 3D model, thus facilitating the identification of layers according to differential sediment supply at the basin scale.…”