## 3 Results and Discussion  
### Gpr  
Equations (2) and (3) were used during the calibration and post-processing to identify locations with potential leakages. Table 6 summarizes the dielectric constants for the soil used in the current study at different moisture contents. The dielectric constants were determined using the known distance of the steel plate used during calibration and the propagation velocity (V) of the electromagnetic waves for each case. The dielectric values were used during the post-processing to interpret the data/images. However, due to the space limitations and objectives of the investigation, detailed discussion of the processing of the GPR images was not possible.  
The GPR was used on pipe 1 and pipe 2 to detect leaks in the pipes. However, the GPR could not be used on pipe 4 (faulty joint). This is due to the rate of water leakage from the joint that was higher in comparison to pipe 2 (crack) and pipe 3 (hole). Consequently, the water quickly reached the surface of the sand, forming surface ponding. This scenario represents one of the conditions (limitations) that the GPR cannot be used in because of the conductivity and increasing signal attenuation, therefore no images will be produced. Hence, experimental data presented will not include data for pipe 4.  
The data was collected every hour and the total duration of the experimentation was three hours. A total of three scans per pipe were taken. In addition to this, the readings were taken to the left, center, and right of the pipe to ensure a complete coverage of the area surrounding the pipe. Thus, in Figure 9, it was observed that each time interval has three GPR images: left, center, and right. The leaks were detected in the images obtained from the GPR. In addition, Equations (2) and (3) were used to calculate the travel time of the pulse and confirm the existence of potential leakage. With an increase in the duration of leak, the development of haze in the GPR images indicates the presence of leaks, which have been circled in red. It was observed that the GPR was able to detect leaks in the following cases: all three pipe materials and the pipes with the hole and crack. As mentioned before, the GPR was not used for pipe 4 (faulty joint). However, the development of surface ponding itself was an indication of leakage.  
Figure 10 presents the data obtained from the GPR scans on the setups when the moisture content of the dune sand was approximately 5%. Like the previous case (moisture content = 2%), from Figure 10, it was observed that the GPR was able detect leaks in all  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Water Content (\%)** & **Dielectric Constant** \\ \hline
0.00 & 4.0 \\ \hline
2 & 4.8 \\ \hline
5.00 & 8.5 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Dielectric constants at different moister contents.  
three pipe materials and the two types of pipe damages (crack and hole). However, it was observed that the visual inspection of images to find the leaks was more strenuous when the moisture content was 5% in comparison to the case in which the moisture content of the dune sand was 2%. Figure 11 presents the data obtained for the GPR when the moisture content of the dune sand was 10%. Contrary to the previous cases, the GPR was only able to detect the leak in pipe 2 (crack) in the PPR setup and in pipe 3 (hole) in the PE setup. It may be this way because a high saturation of soil reduces the ability of GPR to identify the contrast between the water coming out of the leak and the soil moisture.  
Figure 9: GPR images obtained on PPR, PVC and PE setup with 2% soil moisture content.  
Figure 10: GPR images obtained on PPR, PVC and PE setup with 5% soil moisture content.