This project aims at modeling the fate of munition surrogates displaced over or buried into the heterogenous sedimentary bed of a micro-tidal estuarine site, subjected to both fluvial and marine forcing. Project objectives are: (1) to observe directly the combined effect of river flow, water waves and tide on the mobility and burial of underwater unexploded ordnance (UXO); (2) to predict the processes of mobility and burial of UXO subjected to the combined action of river discharge and waves in a micro-tidal environment characterized by mixed sediments (from gravel and sand to silt and clay). Field observations of surrogate mobility and burial will be carried out and used to validate a specifically tailored numerical model, which will be exploited to understand the UXO behavior in estuarine environments characterized by multiple forcing actions and mixed sediments, but also to predict UXO fate due to different environmental conditions. While studies have been largely focusing on surrogate fate in underwater sandy environments (MR-2320, MR-2319 and MR-2503), less knowledge exists on sites characterized by cohesive sediments (MR-2730). Furthermore, to the project team’s knowledge, no studies exist on UXO mobility and burial in estuarine environments, where riverine and marine forcing interact over a heterogeneous bottom.

This project aims at investigating the process of mobility and burial of UXO in a microtidal estuarine environment, characterized by the interplay between river and marine forcings over a heterogeneous soil made of a mixture of cohesive and non-cohesive materials. Preliminary numerical simulations will be run and used to design a field experiment at the Misa River estuary (Senigallia, Central Italy), based on a numerical setup calibrated using available field data collected at the site of interest and already used to analyze important hydro-morphodynamic estuarine processes. The project team will use the final reach of the river as a natural-scale laboratory, bounded by concrete-wall embankments, the whole estuarine area being monitored by an existing, integrated system of sensors installed inland, as well as in both river and sea.

The planned field experiment aims at investigating the fate of UXO in such a complex environment and will leverage the existing sensors to properly frame the hydrodynamic forcings affecting the site during the experiment. Since the final fate of UXO mainly depends on their bulk density, a suite of cylindrical surrogates will be deployed at several locations in the estuarine area, after careful bathymetric and sedimentological surveys and based on the preliminary numerical modeling.

Subsequently, the Delft3D modeling suite will be used to reproduce the hydro-morphodynamics of the environment observed during the field experiment, and then coupled to mobilization models suited to describe the fate of objects lying on the riverbed and seabed. The observed UXO behavior will be first reproduced to attain model validation; afterward, the modeling suite will be exploited for the prediction of UXO mobility and burial under different and extreme forcing scenarios. Mobility and burial of UXO will be thus characterized as functions of different forcing actions and bed material.

Field observations will provide a baseline data set for verification and calibration of the model set up to predict munitions mobility and burial. The expected payoff of the research and development under this effort includes preliminary answers to the questions below.

• Are classical numerical models easily implementable to simulate UXO mobility and burial when subjected to multiple forcing actions (from river and sea) and placed over mixed soils?
• Can a simple classification system to forecast the probability of mobility and burial for individual storm/flood events be developed, accounting for all forcing actions at stake?
• When is it practical to manage munitions in place versus performing remediation?