Nearshore Dewatering for Cost-effective Underwater Munitions Removal
Claudio Fassardi | Jacobs Government Services Company
The objective of this project, at the former Vieques Naval Training Range (VNTR) in Vieques, Puerto Rico, is to assess the feasibility of and develop guidelines and procedures for using cofferdams constructed with water-filled geotextile tubes to dewater nearshore areas to perform munitions removal faster, safer, and more economically with conventional land-based methods.
A variety of deployable flood barrier technologies are in the market to construct cofferdams in the nearshore environment. While most are very effective in withstanding hydrostatic loads and can be configured to prevent occasional flood water overtopping, geotextile tube-type barriers are likely the most appropriate due to their structural and modular characteristics. Compared to the labor-intensive, dangerous, and costly underwater remediation methods currently used in wave-exposed nearshore environments, the use of cofferdams for dewatering is a novel approach that can allow for faster, safer, and more economical nearshore munitions removal by creating temporary conditions where conventional land-based munitions removal methods can be employed. Geotextile cofferdams’ ability to withstand wave loads and prevent wave overtopping at levels compatible with munitions removal work has yet to be determined, so Jacobs Government Services Company (Jacobs) suggests an approximately six-month-long prototype-scale field demonstration at the former VNTR to determine if this technology meets the objective of the project. Based on an extensive knowledge of the Vieques nearshore environment derived from many years of onsite investigations, and the existing infrastructure to support the project, Jacobs selected the former VNTR for the project. The physical and metocean conditions at the former VNTR are representative of United States Navy impacted coastal sites around the globe and, in addition, the project team has already successfully performed a nearshore munitions removal project using a water-filled geotextile tube cofferdam in a relatively small wave-protected area at former VNTR. The success of this similar project spurred the project team to consider the same technology for use in larger and deeper nearshore areas. At selected locations and for estimated land-based munitions removal durations, the project team will construct cofferdams and assess their stability, structural condition, and ability to maintain dewatered areas while exposed to wind, waves, and varying water levels. The results of the project will also yield valuable information to enhance geotextile tube design and cofferdam construction with respect to these conditions.
Using a land-based approach to munitions removal in nearshore areas represents a potential seminal innovation in terms of safety and cost. The nearshore is where recreational use is the highest, resulting in the greatest potential for human contact with munitions. It is also where underwater removal may not be feasible or implementing diver or marine equipment-based underwater removal technologies and methods would be difficult, labor-intensive, and costly. For hundreds of coastal sites covering millions of acres (SERDP-ESTCP, 2010), a land-based approach to munitions removal in the nearshore through cofferdam construction represents not only significant cost savings but also an accelerated rate of munitions removal. The project team will develop guidelines and procedures to inform and allow for future munitions removal in the nearshore with less risk and uncertainty using cofferdams constructed with water-filled geotextile tubes.