Spatio-Temporal Trend Analysis of Total Suspended Solids (TSS) for the 2018-2025 Period Using Sentinel-2 Near-Infrared Band 8 Regression Model (Case Study: Gajah Mungkur Reservoir, Wonogiri)

Abstract

Sedimentation poses a major threat to the sustainability of the Gajah Mungkur Reservoir (WGM) as a strategic water resource infrastructure. This study aims to map the spatial-temporal dynamics of Total Suspended Solid (TSS) in WGM using Sentinel-2 MSI satellite imagery for the periods of 2018, 2022, and 2025. The method integrates in-situ measurements with reflectance extraction from the Near-Infrared channel (Band 8). Linear regression analysis yielded a TSS estimation algorithm with very high accuracy, indicated by a Coefficient of Determination (R²) of 0.969. Mapping results reveal that sediment distribution is heavily influenced by climate variability. In dry years (2018 and 2025), sedimentation was concentrated in marginal areas due to resuspension mechanisms, while the reservoir's main body remained relatively clear. Conversely, the wet climate anomaly (La Niña) in 2022 triggered a massive turbidity spike covering the entire reservoir surface. Crucially, the study identifies the Keduang Sub-watershed as a consistent and dominant sediment pollutant source across all seasonal conditions. Consequently, reservoir management strategies must prioritize source-control erosion management through land conservation in the upstream Keduang area rather than relying solely on downstream dredging.