Assessment of seabed munition mobility induced by propeller-generated turbulence
Date
2025
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Publisher
University of Delaware
Abstract
In the years prior to the contemporary environmental movement, navies around the world dumped unused munitions overboard for disposal. In 1972, the London Convention banned many pollutants, including munitions. Half a century since, these potentially live munitions can come onshore or be uncovered by erosion, posing serious risks to the public. Among the mechanisms driving munitions mobility, this study investigates the influence of propeller generated turbulence on munitions transport. The experiment used a large pool with a sediment bed and a proud munition model (also referred to as target). An overhead outboard motor was used to simulate vessel propeller wash. Results showed munition density was a parameter governing target stability under propeller-generated flows. Targets constructed to emulate high density conventional munitions demonstrated strong resistance to displacement by not exhibiting movement under tested flow regimes. In contrast, movement was observed only when the targets were configured to be less than half as dense as conventional ordnance. Detailed measurements further established that the magnitude of target displacement was governed by density and sensitive to spatial proximity to the propeller; targets positioned near the point of maximum jet velocity experienced substantially larger mobilization. The patterns affirm that, in deep-water scenarios where propeller-induced turbulence dissipates rapidly and munitions remain dense, the overall risk of large-scale munition migration is low. Nevertheless, there is a heightened vulnerability for less dense munitions or scenarios characterized by high-energy, confined settings—such as navigation channels and high traffic port facilities—where persistence of strong, localized flows can present a mobilization threat. The ability to predict munition movement, combined with general historical disposal data are crucial to predict when/where expected munitions may arise. Local authorities can then exclude the populace until ordnance experts can properly dispose of them in a safe and formal process, akin to the Iron Harvest in northern France.
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Keywords
Munitions transport, Environmental movement, Pollutants, Erosion