An Investigation on the Geologic, climatic, and anthropogenic controls on the morphology of the Progo River, Indonesia

This study investigates the geologic, climatic, and anthropogenic factors controlling morphological changes along the Progo River in Daerah Istimewa Yogyakarta (DIY), Indonesia. The CAESAR-Lisflood model was applied to assess the relative effects of climate and geology on watershed morphology and sediment discharge, with validation using Google Earth Engine (GEE). Datasets including GEE imagery, a geological map, Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM), field observations, and petrographic analysis were integrated to identify morphologic changes related to geological conditions. Comparison of GEE images from 2002 and 2022 produced a morphology change map that highlighted erosion and accretion zones over two decades. Normalized Difference Vegetation Index (NDVI) analysis, combined with rainfall data, was used to evaluate climatic impacts, while fieldwork and community interviews provided insights into human influences. Results indicate that lithology, geological structure, slope, and grain size strongly influence river morphology. Larger boulders and resistant bedrock limit erosion, whereas fine-grained and weakly consolidated sediments in lower reaches erode rapidly, especially under heavy rainfall. Limestone exhibits lower resistance to erosion than volcanic breccia. Annual precipitation data show no significant long-term trend, and seasonal variability could not be assessed, suggesting only a limited climatic role. Anthropogenic factors—including dam construction, quarrying, and land use changes—emerge as the most significant drivers of morphological change. Additionally, the 2010 eruption of Mount Merapi contributed large volumes of loose material, temporarily enhancing sediment transport. These findings underscore the combined but unequal influence of natural and human factors on river system dynamics.