Hydrography, dredging, and safe navigation on the Hugli

The Hugli's channels and bars changed fast enough that pilots sometimes needed fresh depth information with each tide. A river survey service of about 25 officers kept track of those changes, displaying the latest soundings on blackboards aboard survey launches. Two survey ships produced charts for channels and less changeable bars, while shore teams at Kolkata and Hugli Point covered their own sections. The port commissioners operated three dredgers, with at least two continually working and two surveyors living aboard each. Their soundings directed dredging toward the most urgent shoals and told pilots already moving along the river which tracks remained usable. Annual winter surveys triangulated the banks and took soundings across the river's full width and length.