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 GPR and verified by manual measurement suggests 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; however, 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.

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(Spain) C/ Marti i Franques sin 08071-Barcelona 1.-INTRODUCTION Commissioned by the Spanish Authority of Culture a geophysical survey using GPR has been carried Out in the Roman City Wall of Lugo (Spain). The purpose was the inspection of the City Wall and surrounding areas with the aim of detecting hidden structures of the original building. The starting point of this project was the detection of two double-branch steps during consolidation works in one tower of the City Wal!. Besides, historical notes informed us about the presence of other steps unearthed after collapses near the Obispo Aguirre gate. This facts, together with the achievement of the 'Plan Integra! de Conservaciôn y Restauraciön de la Muralla de Lugo' (Integral Plan for the Maintenance and Restoration of the Roman City Wall of Lugo) lead to undertake the placement of new hidden steps and whichever original structure of the building, by means of non-destructive techniques.

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