Because it projected  into the Piscataqua River channel, Henderson's Point created a navigational hazard for warships visiting the navy yard. Consequently, a cofferdam was constructed, behind which  of rock and  of soil were excavated.
Henderson's Point, located in the Piscataqua River, presented a navigation challenge for ships entering the navy yard. A cofferdam was built to address this issue by creating a safe passage through the channel. The excavation of rock and soil behind the cofferdam helped to create a stable foundation for the structure.