Lake Morphometric Changes, Mahakam, Indonesia

Tropical floodplain lakes serve as dynamic archives of sedimentary and geomorphic processes, yet quantitative, long-term records of their morphometric evolution under anthropogenic pressure remain limited. This study presents a three-decade (1990–2020) geospatial analysis of the three interconnected Mahakam Lakes (Jempang, Melintang, Semayang) in Indonesia—a system designated as a National Priority for conservation. Using multi-temporal Landsat imagery and bathymetric data, we quantified key morphometric parameters including surface area, volume, mean depth, shoreline development index (SDI), and volume development (VD) to assess changes in basin form and complexity. Results reveal starkly divergent trajectories: Lake Melintang experienced severe volumetric loss (approximately 250,000 m³ between 2010–2020) accompanied by a sharp decline in VD from 0.42 to 0.18, indicative of rapid, sedimentation-driven basin infilling. Lake Jempang maintained stable area but exhibited increased shoreline irregularity (SDI rising to 1.3). In contrast, Lake Semayang showed positive volumetric trends and a rising VD, suggesting a more resilient or recovering state. These differential responses illustrate how variable sediment delivery and hydrological connectivity can reshape adjacent lake basins within a single fluvial system. The study establishes SDI and VD as effective geomorphic indicators for tracking sedimentation and shoreline dynamics. Our findings provide a quantitative, process-oriented baseline for understanding sediment budgets and landscape evolution in tropical fluvial-lacustrine environments, while demonstrating a replicable geospatial framework for guiding the management of sediment-related threats in the Mahakam system and similar floodplain lakes worldwide.