## 4 Results and Discussion  
### Changes in Sediment Texture from Borhelo Sample Datasets  
Table 2 shows the characteristic particle sizes and sorting indices obtained for all clastic sediment samples that were extracted from the boreholes. According to these data, different patterns in thickness and sediment texture were found in the alluvial channel-fill: the pattern located in the active channel, characterised by a progressive decrease in the median grain size, and an increase in the sorting index with depth, passing from medium-sized gravels at the surface level to sands and small gravels at the bottom (BH3); the pattern defined in the lateral bars (BH1 and BH4) by a single layer 1 to 1.5 m thick composed of medium and coarse gravels and moderate heterometry (\(2.1<\sigma<2.4\)), directly lying on a softer rocky substrate; and a third pattern in the edge and tail part of a central bar (BH2), where a subsurface level of coarse material is prevalent, mainly gravels with a size dispersion index somewhat smaller than in the previous cases, but noting an abrupt change in texture in depth (a layer with abundant sand 1 m thick and a deeper and slightly thinner mixed layer of sands, gravels, and pebbles). In general, except in the BH2 case, the subsurface detritial layer has a homogeneous thickness, between 1 and 1.5 m, and consists of coarser materials than deep deposits.  
Average values of the Zingg and the Sneed and Folk shape and sphericity indices for each depth interval are shown in Table 3. A common feature in all borehole logs is the decrease in the percentage of rod particles as depth increases. This fact may have conditioned the void ratio and the effective porosity in a similar proportion, also affecting the obtained electrical resistivity values. It is also worth noting the progressive decrease in the I/L ratio in the discoid or oblate class obtained according to the depth for the BH3 borehole. The highest percentages reached in the subsurface layer correspond to the discoid/oblate and rod classes (>80% between both classes), which tend to increase the degree of porosity at this level. On the other hand, the disc-rod index (DRI) and the effective settling sphericity (\(\psi_{\text{p}}\)) do not seem to be decisive for differentiating sediment textures, since they range between 0.38 and 0.51 in the first case and between 0.60 and 0.69 in the second.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Grain Sizes**} \\ \hline  & **Depth (m)** & **D\({}_{\text{10}}\) (mm)** & **D\({}_{\text{20}}\) (mm)** & **D\({}_{\text{50}}\) (mm)** & **D\({}_{\text{84}}\) (mm)** & \(\sigma\) \\ \hline BH1 & 0.0–1.1 & 0.4 & 2.1 & 15 & 36 & 2.37 \\  & 1.1–3.0 & 0.01 & 0.02 & 0.04 & 0.06 & 0.08 \\ \hline BH2 & 0.0–1.4 & 0.4 & 2.5 & 12 & 27 & 2.09 \\  & 1.4–2.3 & 0.2 & 1.1 & 1.9 & 15 & 2.21 \\  & 2.3–3.0 & 0.5 & 2.6 & 17 & 32 & 2.22 \\ \hline BH3 & 0.0–1.2 & 0.4 & 3.3 & 10 & 17 & 1.86 \\  & 1.2–1.6 & 0.3 & 1.9 & 8 & 18 & 2.08 \\  & 1.6–2.5 & 0.4 & 1.4 & 6 & 26 & 2.20 \\  & 2.5–3.0 & 0.1 & 0.5 & 4 & 12 & 2.73 \\ \hline BH4 & 0.0–1.5 & 0.5 & 3.2 & 17 & 27 & 2.11 \\ \hline \hline \end{tabular} BH is the borehole code, D\({}_{\text{10}}\) and D\({}_{\text{20}}\) are the effective grain sizes corresponding to 10% and 20% of the total sample weight (mm), D\({}_{\text{50}}\) is the median grain size (mm), D\({}_{\text{84}}\) is the particle size for 84% of the sample weight (mm), and \(\sigma\) is the inclusive graphic standard deviation (sorting) after Folk (1974).  
\end{table}
Table 2: Representative grain sizes and sorting estimated for clastic sediments in borehole logs. Rambla de la Azohia.