Paradeep Port is located on the delta of the Mahanadi river. A river delta is a landform that forms at the mouth of a river, where the river deposits sediments carried by the flowing water. The Mahanadi river is one of the major rivers in India, flowing through the states of Chhattisgarh and Odisha.

Option 1, Rihand, is incorrect as the Rihand river is not associated with Paradeep Port. The Rihand river is a tributary of the Son river, which is itself a tributary of the Ganga river.

Option 2, Ganga, is incorrect as well. While the Ganga river is one of the major rivers in India, Paradeep Port is not located on its delta.

Option 4, Baitarani, is also incorrect. The Baitarani river is located in the state of Odisha, but Paradeep Port is not situated on its delta.

Therefore, the correct answer is option 3, Mahanadi, as Paradeep Port is indeed located on the delta of the Mahanadi river.