From Halopedia, the Halo wiki
Vadam Harbor is a body of water in the state of Vadam, ruled by the House of 'Vadam, located on the coasts of Yermo on Sanghelios. The harbor is located thirty miles away from Vadam keep and is visible from the keep, with a valley separating the keep from the harbor. Work from the harbor brought in profits for the state.
The harbor is easily accessible from the city of Sunaion, built above the Csurdon Sea. For this reason, Sunaion was occupied by Jul 'Mdama's Covenant in October 2558 when the faction plotted an attack on Vadam.