Application of ground-penetrating radar to the identification of subsurface piping in blanket peat

Abstract

Natural soil pipes are common and significant in upland blanket peat catchments yet there are major problems in finding and defining the subsurface pipe networks. This is particularly important because pipeflow can contribute a large proportion of runoff to the river systems in these upland environments and may significantly influence catchment sediment and solute yields. Traditional methods such as digging soil pits are destructive and time-consuming (particularly in deep peat) and only provide single point sources of information. This paper presents results from an experiment to assess the use of Ground Penetrating Radar (GPR) to remotely sense pipes in blanket peat. The technique is shown to be successful in identifying most of the pipes tested in the pilot catchment. Comparison of data on pipes identified by the GPR and verified by manual measurement suggest that pipes can be located in the soil profile with a depth accuracy of 20 to 30 cm. GPR identified pipes were found throughout the soil profile except that those within 10 – 20 cm of the surface could not be identified using the 100 or 200 MHz antennae due to multiple surface reflections. Generally pipes smaller than 10 cm in diameter could not be identified using the technique although modifications are suggested that will allow enhanced resolution. Future work would benefit from the development of dual frequency antennae that will allow the combination of high-resolution data with the depth of penetration required in a wetland environment. The GPR experiment shows that pipe network densities were much greater than could be detected from surface observation alone. Thus, GPR provides a non-destructive, fast technique which can produce continuous profiles of peat depth and indicate pipe locations across survey transects