Due to input of sediment from rivers, marine deltas may form, due to beach and longshore drift such features as spits, bay barriers, and tombolos may form. Depositional Features along coasts. An example is the Mississippi River Delta, which is composed of several lobes that were deposited within the last several thousand years. Erosion of the older delta lobes has taken place due to subsidence, sea level rise, and lack of new sediment being supplied to the delta because of the human-made levee system. Spits - elongated deposits of sand or gravel that projects from the land into open water.
Spits usually form at the mouth of a bay due to long shore current and beach drift.
Generally they curve inward towards the bay due to refraction of the waves around the mouth of the bay. Bay Barriers - if a spit extends across a bay, it is called a bay barrier. Exchange of water between the bay and the ocean is accomplished through the groundwater system. Tombolos - a spit that connects the mainland to an offshore island is called a tombolo. Barrier Islands - A barrier island is a long narrow ridge of sand just offshore running parallel to the coast.