Chronological Reconstruction of the Hydraulic Landscape at Prasat Sdok Kok Thom Using OSL Dating

Monthon Yongprawat1*, Tawanrat Chainarapipat2, Pimchanok Pongkasetkan3, Sasiphan Khaweerat1, Alisa Chaiwong1, and Chalermpong Polee1

Sadok Kok Thom is a significant ancient Khmer‑style sanctuary located on the Thai–Cambodian border in Sa Kaeo Province, Thailand. Two large earthen embankments have been identified near the monument, namely the Baray and the Lalom, which have been interpreted as irrigation features; the Baray functions as a water reservoir for ritual and religious activities. The L‑shape of the Lalom was presumed to be an embankment or floodwall. However, anthropogenic landscape modifications visible in satellite imagery have obscured original surface flow directions and complicated functional assessments. To clarify these roles and to gain a deeper understanding of the mechanisms and functions of these irrigation systems, five trench excavations and OSL dating of soil samples were applied. Stratigraphy reveals that both the original Baray and Lalom exhibit asymmetrical bell‑shaped morphologies. The original Lalom had a higher crest and relatively narrow base, with an elevation that closely matches documented modern peak flood levels. The study suggests that the Lalom was likely designed as a floodwall to mitigate short‑term flooding around the monument by redirecting excess surface water toward the Baray, whereas the embankment of the Baray has a broader base and lower elevation. In addition, isotope and chemical analyses indicate minimal surface water–groundwater interactions. This morphology implies deliberate engineering for structural stability and long‑term water retention, potentially operating as a reservoir for both ritual use and domestic consumption. Collectively, the sedimentological and chronometric evidence supports the interpretation that the Lalom embankment formed part of a hydraulic management system either diverting runoff into the Baray for storage or acting as a barrier to limit direct inundation of the monument precinct.