## 3 Results and Discussion  
### Detection of Wetting Zones through GPR Data  
The GPR-based delineation of the wetting bulb at the Ottawa site is presented. The 3D renderings (Figure 2a,e) distinctly outlined the dimensions and configurations of the \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Soil Physical Quality Indicator** & **Description** & **Ranges or Critical Limits** & **Evaluation Class** \\ \hline \(\text{Macporosity},P_{MAC}\) [m\({}^{3}\) m\({}^{-3}\)] = & Soil’s ability to quickly & \(\geq\)0.07 & optimal \\ \(\theta_{s}-\theta_{m}\) & drain excess water & \(0.04\leq P_{MAC}<0.07\) & intermediate \\  & and facilitate root & \(<\)0.04 & poor \\  & proliferation & & \\ where \(\theta_{m}\) [m\({}^{3}\) m\({}^{-3}\)] is the saturated volumetric water content of the soil matrix, corresponding to \(h=-0.1\) m. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._wetting bulb generated during both the tension and Beerkan infiltration tests conducted on the identical surface area. Initially, the infiltration bulbs were identified through a comprehensive 360-degree examination of the 3D renderings. Subsequently, horizontal and vertical cross-sections were extracted from the 3D models to pinpoint regions with significant reflection differences, indicative of wetted soil patches beneath the primary wetting front (Figure 2: TI test in subpanels b-d and Beerkan test in subpanels f-h). These cross-sections were then compared with the direct observations of the infiltration bulb, exposed by sectioning the soil along a vertical plane at the conclusion of the third GPR survey (Figure 1). The congruence between the observed shapes provided a robust indication of the accuracy of the 3D interpolation procedure in mapping the wetted patterns. This finding corroborated the experimental results of a prior study by [PERSON] et al. (2020). During the tension infiltration (TI) test, an applied suction of 30 mm (equivalent to a water pressure head of \(-30\) mm) restricted water flow to the soil matrix, thereby excluding pores with radii > 0.5 mm from the infiltration process ([PERSON], 2018). The comparison of radargrams  
Figure 2: Three-dimensional representations of the wetting zones obtained from ground-penetrating radar surveys conducted before and after wetting, during (**a**) tension and (**c**) ponding infiltrometer experiments at the Ottawa site. Panels (**b,f**) illustrate horizontal cross-sections taken from the 3D models at a depth of \(-0.1\)m from the soil surface. Panels (**c,g**) present vertical cross-sections oriented north–south with a view to the east, while panels (**d,h**) show vertical cross-sections oriented west–east within a view to the north. The red arrows highlight the detected flow channeling through the limestone layer (see Figure 1 for reference). from the initial and subsequent GPR surveys enabled us to discern amplitude variations attributable to water movement within the matrix flow region. As anticipated for capillary-driven infiltration, the resulting wetting bulb exhibited a regular, quasi-hemispherical configuration with a uniform water distribution (Figure 2a,b), primarily extending through the upper soil horizon to an approximate depth of 0.3 m (Figure 2c,d). The differentiation between the repeated radargrams of the first and third GPR surveys allowed us to highlight the amplitude fluctuations as a result of the water infiltrating throughout the entire pore system More specifically, in this case, the wetting bulb is the result of the water infiltrated during both the TI and Beerkan tests, which were carried out on the same infiltration surface. During the ponding test, given that the smaller pores were already filled, the water movement occurred mainly into the larger pores (>0.5 mm), determining a smaller wetting pattern in comparison to that generated during the TI test, which highlighted the occurrence of a mainly vertical gravity-driven movement through the topsoil [50], as shown from the dye pattern in Figure 1 (Step 6: Soil excavation).