The contribution of geophysics to archaeology: a case study of an ancient canal of the Oc Eo culture in the Mekong Delta, Vietnam

Generally, underground ancient canals are infilled with alluvial materials, with the canal bed and substrate often having different resistivity values. This study aimed to determine the location and morphology of Malleret’s ancient canal 16 located to the southeast of the Ba The mountain, Mekong Delta, Vietnam by means of geophysical techniques. Two geophysical methods were used: electromagnetic profile and electric resisitivity tomography. A geoelectric structure 70 m long with 70–95 mS/m of apparent conductivity was found. On the electrical resistivity tomography section, a resistivity zone of 10–20 Ω∙m, 1–4 m deep, 70 m wide corresponds to the mentioned above geoelectric structure, which is in an asymmetric U-shape extending toward the southeastern bank of canal 16. Hand-augering confirmed that the canal bed is fully incised into Holocene sediments as a substrate which stretches down to the Pleistocene. The sediments are composed of loams mixed with plant remains with a resistivity ρ ~ 10–15 Ω∙m. Both of the canal banks at a depth of 5 m are made up of Holocene sedi-ments (ρ ~ 4–10 Ω∙m). The 14C measurements determined the age of the organic matter in the canal as being equal to 1210 ±85 BP, suggesting canal 16 ceased being operational at that time. The precise positioning of canal 16 on the ground surface, as well as identifying the morphology of the canal bed, were corroborated by geophysical techniques. The obtained results are of considerable value to archaeologists.