Hydrodynamic Control of Suspended Sediment Transport and Coastal Morphodynamics in Tropical Estuarine Systems Under Environmental Pressure: A Case Study of Balikpapan Bay

Abstract

Balikpapan Bay has large and small river estuaries, including the Sepaku River, the Wain River, and the Riko River. The watershed of Balikpapan Bay has a fairly important and strategic role, including as a buffer for the sustainable function of the bay as a seaport for Balikpapan and a source of income for the surrounding community as well as the life of the bay's marine ecosystem.The purpose of this study was to determine the distribution pattern of Total Suspended Solid (TSS)s and changes in the morphology of Balikpapan Bay based on the tidal flow pattern model using the 3-dimensional Mohid model approach. Data collection was carried out on 3^rd-20^thSeptember 2024. The model used is a hydrodynamic model with bathymetry data and tidal data as the main drivers and secondary data, namely the constant Total Suspended Solid concentration as the input value in model processing. The distribution of very high Total Suspended Solid concentrations occurs at full moon tide until it reaches the mouth of Balikpapan Bay, the area with the highest sediment concentration, namely the Sepaku Bear River ranges from 200-250 mg.L^-1 and at the mouth of Balikpapan Bay it ranges from 50-100 mg.L^-1. Erosion occurs in the Jenebora area, part of the Kariangau area, and the eastern part of the bay, especially on the coast of Kemala Balikpapan. The observed pattern—elevated TSS during neap or spring-tide conditions and near the estuary mouth, tidal forcing and riverine inputs shape SSC distributions and estuarine turbidity maxima (ETM). Balikpapan Bay could develop an ETM in the vicinity of the river mouths or the estuarine channel mouth under similar forcing, with stronger sediment exchange during higher-energy tidal phases. The Balikpapan Bay results indicate a robust coupling between tidal flow, sediment transport, and estuarine morphodynamics, with significant implications for port operations, coastal resilience, and ecosystem health. High TSS in riverine plumes and erosion hotspots along the coast imply a dynamic sediment regime that will influence dredging needs, shoreline stability, and habitat conditions.