Mobility and Burial of Munition Surrogates in the Inner Surf and Swash Zones

Abstract

Unexploded ordnance (UXO) resulting from past military activity are present in coastal settings. Mobility of UXO, specifically in the inner surf and swash zones, constitutes a potential risk for the public. Mobility or exposure may increase under energetic events due to enhanced forcing or sediment erosion. Yet, the conditions leading to exposure, burial, or movement of UXO remain poorly understood. A large-scale laboratory wave flume (120 m x 5 m x 5 m) study at the Institut national de la recherche scientifique (INRS) in Quebec City, Canada was carried out from July 7 to September 23, 2022 to quantify surrogate UXO mobility and burial. An undistorted, scaled beach profile from Mantoloking, NJ, USA was constructed using 0.28 mm diameter sand. Eighteen stations were established at roughly 5 m intervals to collect hydrodynamic, sediment process, and morphology data and to quantify surrogate UXO behavior. Over 150 surrogates of varying bulk density were distributed throughout the flume. Waves were forced in 300-wave packets for each trial of a condition case. Cases used different wave heights, water levels, and wave periods. Preliminary results indicate berm erosion with increasing hydrodynamic energy. The dune only experienced erosion at the highest water levels. Surrogate UXO generally remained in place and buried partially or migrated offshore. Migration tendency and distance was a function of the surrogate density.