Technologies to temporarily dewater impacted nearshore areas to allow for faster, safer, and more economical munitions removal would be a valuable new tool in the long-standing problem of addressing explosive hazards in this area. Among the various technologies available, a cofferdam constructed with water-filled geotubes was determined to be the most adequate for the purposes of this Demonstration in part because it was a readily available technology that required minimal adaptation for the intended use. 

The objectives of this Demonstration were to:

1. Assess the feasibility and develop guidelines and procedures for using temporary, portable cofferdams constructed with water-filled geotubes to dewater nearshore areas, thereby facilitating munitions removal faster, safer, and more economically with conventional land-based methods. 
2. Provide a technology to make the nearshore a safer environment for recreational users and military operations.

In March 2024, Jacobs Government Services Company constructed a temporary and portable, prototype-scale 600-foot-long cofferdam in the nearshore of the former Vieques Naval Training Range in Vieques, Puerto Rico. The cofferdam was constructed in a nominal five-foot water depth and consisted of five individual water-filled geotubes joined together with connection collars.

This Demonstration was not successful in fully dewatering the nearshore area. However, it did show that temporary, portable structures such as water-filled geotubes can be effective breakwaters that provide a wave- and current-free area, thereby allowing cost-effective munitions removal in areas where this has been difficult to date. As a breakwater, the cofferdam used in this Demonstration calmed the surf, thereby allowing munitions divers to survey the wave- and current-free area landside of the breakwater and ultimately remove 41 anomalies detected during the survey. This technology can be a valuable tool in terms of safety and cost, as it overcomes the conditions (i.e., waves and currents) that make munitions removal in nearshore areas significantly affected by waves and currents with divers and/or equipment difficult.

Recognizing that this Demonstration did not successfully dewater the nearshore but also acknowledging that with the modifications discussed in the Final Report, dewatering may be possible, a cost-benefit analysis for munitions removal associated with dewatering versus calming the nearshore area (i.e., Cofferdam & Dewatering versus Breakwater) was performed. The cost benefit analysis showed that, even if dewatering was possible, the cost of using water-filled geotubes as a Cofferdam & Dewatering alternative for munitions removal would be approximately two times that of using water-filled geotubes as a Breakwater. Although the cost-benefit analysis assumed the use of water-filled geotubes for both the cofferdam and breakwater construction, alternative mobile structures, such as portable, submersible barges, may be appropriate to consider for future applications.

Also noteworthy is that even though the cost-benefit analysis assumes dewatering may be possible with portable, water-filled geotubes, that outcome is currently unknown. In the future, if dewatering is deemed preferrable for a particular situation, the ability of a cofferdam constructed of water-filled geotubes to achieve and maintain a dewatered state would need to be demonstrated before its application is considered.

The standard geotubes material seemed too thin and small leaking holes developed, the standard filling hoses were relatively few and small diameter which required retrofitting the tubes, and joining tubes with connection collars was imperfect, leading to seepage and the inability to completely dewater the enclosed area. (Project Completion - 2025)