Preliminary Geoarchaeological Sensitivity Assessment of the Proposed Ancient Opak River Diversion Site Associated with Prambanan Temple, Indonesia

Abstract The Prambanan Temple Complex, one of Indonesia's UNESCO World Heritage Sites, was constructed during the 9th century CE within a landscape shaped by both natural processes and human intervention. The Siwagrha Inscription suggests that the Opak River was diverted to prevent its course from intersecting the sacred temple grounds, while previous geomorphological interpretations indicate that the proposed modification may represent a form of pre-industrial anthropogenic landscape intervention. Despite its potential significance for understanding long-term human–environment interactions during the Ancient Mataram period, the proposed ancient Opak River diversion has received limited attention from geoarchaeological and geoheritage perspectives. Its potential heritage significance is particularly relevant because the proposed site is situated within the broader landscape of the Jogja National Geopark and the Bayat Purba Aspiring Geopark, where geological, geomorphological, and cultural heritage values are increasingly considered within integrated landscape management. This study presents a preliminary geoarchaeological sensitivity assessment of the proposed ancient Opak River diversion associated with the Prambanan Temple Complex. The assessment integrates geoarchaeological significance, threats, and vulnerability using inscriptional evidence, geomorphological observations, and existing archaeological studies. The proposed diversion corridor obtained a high Geoarchaeological Significance Value (76.19%), reflecting its rarity and strong association with the archaeological landscape of Prambanan. It was assessed as having moderate threat (42.30%) and moderate vulnerability (44.44%), resulting in a low Geoarchaeological Sensitivity Value (24.67%). Although the low sensitivity value indicates that the proposed feature is not currently an immediate conservation priority, its high geoarchaeological significance warrants continued attention, particularly in view of ongoing anthropogenic modification of the river corridor. The results demonstrate the potential of a preliminary sensitivity assessment to identify geoarchaeological features that may contribute to integrated geoheritage management within geopark landscapes. However, the proposed ancient Opak River diversion remains an interpretation based on currently available inscriptional, geomorphological, spatial, and archaeological evidence and requires further multidisciplinary investigation for empirical validation. This preliminary assessment therefore provides a baseline for future geoarchaeological research and for considering the proposed feature within the broader geoheritage and cultural-landscape management frameworks of the Prambanan World Heritage, Jogja National Geopark, and Bayat Purba Aspiring Geopark landscapes.