Drilling Speed Modeling for River-Sediment Classification Based on Response Surface Methodology: In Case of Taedong River, DPRK

Accurate sediment classification is fundamental to understanding riverbed dynamics, geomorphological evolution, and supporting the planning and implementation of water resource management and civil engineering projects. In the Democratic People’s Republic of Korea (DPRK), conventional sediment sampling methods are severely constrained by logistical and technical limitations, creating an urgent need for rapid, cost-effective, and reliable alternative approaches. This study proposes a novel modeling framework that leverages drilling speed, measured during shallow rotary drilling, as a diagnostic parameter for sediment classification in the Taedong River. A Response Surface Methodology (RSM)-based experimental design was adopted to systematically investigate the statistical relationships between the rate of penetration (ROP) and key sediment properties, including median grain size (D50), bulk density, moisture content, and consistency. Fieldwork involved drilling 18 boreholes across the upper, middle, and lower reaches of the Taedong River, complemented by comprehensive laboratory analysis of sediment samples. The developed second-order RSM model exhibited strong predictive performance with a coefficient of determination (R²) of 0.92, enabling the classification of sediments into four primary categories: clay, silt, sand, and gravel. Validation against gold-standard laboratory grain-size analysis yielded an overall classification accuracy of 87.5%. This modeling framework offers an efficient, minimally invasive, and cost-effective solution for river sediment assessment in data-scarce regions. Its application not only enhances sediment monitoring capabilities in the Taedong River but also provides a scalable template for similar fluvial systems globally, particularly in areas where conventional sampling is impractical. The findings contribute to advancing sediment science and support evidence-based river management, hydraulic engineering, and ecological conservation efforts.