Water Pixel Dilution Bias: A Systematic Measurement Error in Riverine Spatial Feature Engineering

This study identifies and formalizes Water Pixel Dilution Bias (WPDB), an overlooked measurement error where river water pixels distort surrounding land use calculations in standard circular GIS buffers. We derive an exact mathematical formula to predict this bias and validate it across 11 monitoring stations on two rivers in Dhaka, Bangladesh. We also provide a practical flow aware normalization method to correct this distortion in everyday GIS and environmental data science workflows.