Nautical Depth for US Navigable Waterways: A Review

The present state of navigation engineering knowledge concerning nautical depth in ports and waterways with fluid mud is summarized to examine the potential for successful application of the nautical depth concept in U.S. navigable waterways. Nautical depth defines a safe and effective channel bottom criterion in areas where fluid mud confounds conventional acoustic (echo sounder) surveying methods. Fluid mud is a high-concentration suspension that typically behaves as a non-Newtonian fluid. It occurs in ports and channels on all U.S. coastlines and accounts for a significant portion of the United States' $1 billion dredging expense. Nautical depth has been adopted in multiple ports on three continents. Where nautical depth application is appropriate, it often reduces dredging frequency and dredged material volume and can provide water quality benefits. Multiple experiments and field experience have shown that vessels can safely transit areas with fluid mud below the keel. The United States' adoption of the nautical depth concept for select ports and waterways can be expected to reduce dredging frequency and volumes. It offers potential economic and environmental benefits but will require a consensus among federal, state, and local organizations with responsibilities for constructing, operating, maintaining, marking, and using navigable waterways.