The long-term goal of this project is to quantify the forcing processes and associated migration, exposure, and burial of variable density munitions in the surf and swash zones. The pressing objectives are: 1) to determine the importance of bulk density and munitions roughness, potentially through time-sensitive degradation processes, to munitions migration, exposure, and burial; and 2) collect and analyze needed data on munitions processes in extreme forcing conditions that are likely the most important for migration, exposure, and burial.
The project team will design and conduct small-scale, dam-break laboratory tests for initial understanding of variable density munitions migration and exposure. Results will be used to narrow the parameter space and inform subsequent prototype-scale testing. Prototype-scale tests will be designed and conducted in the 300 meter (m) long GWK flume (Hannover, Germany) where wave heights up to 3 m and water levels can be altered to mimic extreme storm events. The project team believes munitions migration and exposure are rare events occurring mostly during energetic conditions and that storm onset and variable munitions densities enable some munitions to migrate or become exposed while others remain in place via scour burial. Fabricated surrogate munitions generally have two characteristics that can impact munitions mobility studies: first, often only a single iteration of a particular caliber is constructed, and second, the fabricated surrogate is pristine with no time-sensitive imperfections. The project team believes it is necessary to address both of these aspects in detailed studies. Additional surrogate munitions will be designed and constructed where bulk density is purposefully altered through caliber iteration and also modified through the simulation of corrosion, perforation and biofouling/encrustation via “low-density” roughened munitions coverings. Other physical characteristics (e.g. rolling moments and center of gravity) will be maintained where possible. Surrogate munitions and sensors to quantify the local hydrodynamics and morphology will be deployed throughout the surf and swash zone (as well as offshore) providing forcing and response characterization for parameterizing migration, exposure, and burial.
The measurements will provide needed data under extreme forcing for the validation/calibration of models presently under development within the Munitions in the Underwater Environment SERDP thrust. Namely, probabilistic (MR19-1126, MR-2733) and highly resolved physics-based models (MR-2732) of munitions migration, exposure, and burial. The measurements will allow the project team to address key questions: What is the fundamental role of bulk density for munitions mobility, exposure, and burial in the surf and swash zones? What wave conditions (storm return interval, storm onset) are required to cause variable density munitions to become exposed and/or mobilized; with specific emphasis on what conditions are needed for onshore transport? How do munitions become located on the beach face where there is the highest chance of receptor contact? What is the relative importance of corrosion, perforation, and/or biofouling on munitions mobility, exposure, and burial (reduced bulk density vs. increased bottom drag).