Monthly monitoring of suspended sediment variability using bottle samplers in the LUSI outfall area of the Porong River

Monitoring suspended sediment concentration (SSC) is important for understanding sediment dynamics in extreme tropical rivers influenced by both natural and human activities. The Porong River in East Java constantly receives sediment input from LUSI (short for Lumpur Sidoarjo), a hot mud volcano formed after a drilling incident at Banjar Panji-1 in May 2006. The eruption inundated over 6.3 km² of settlements, farmland, and infrastructure, displacing about 30,000 people and causing persistently high sediment loads with extremely turbid flows. This study developed a field-based SSC sampling method by modifying the USDH-48 bottle, replacing standard rods with flexible ropes for manual operation of orientation and depth in deep, high-energy flows. The method uses a systematic spatial-vertical sampling strategy across several cross-sections to capture sediment variability. In contrast to ASTM D3977-97, which is designed mainly for shallow, steady-flow rivers, this method accommodates greater depths and unsteady-flow rivers through flexible deployment and structured sampling coverage. Over one year, monthly monitoring produced 864 samples. Validation against a messenger-system vertical sampler at the same location and depth showed strong statistical agreement (R² > 0.80; RMSE < 20 %). Adaptive field methods based on the modification of USDH-48 for extreme tropical rivers. Structured design capturing spatial and vertical sediment variability. Statistically validated against an established vertical water sampling system.