The point at which the marine waters meet the river (fluvial) system is considered a delta. The river delta types are dependent upon the surrounding characteristics of the landscape and water flows. For instance, whenever a stream feeds into a river it also forms a delta. Subaqueous and subaerial sedimentary deposits at the junction form the deltas and different levels and different formations. You can find river deltas in every part of the world aside from the Arctic and Antarctic regions.
Each river delta has certain things in common. These include large drainage basins, mouths of large river systems, huge amounts of sediment moved by the water's flow and no nearby geologically active coastlines.
The anatomy of a delta is similar to each type as well. The subaqueous are underwater deltas that have a portion below the low tide mark with seaward particles becoming finer and finer. Subaerial are slightly above the water and low tide mark. Lower delta plains are indicative of the marine and fluvial junction that extends towards land. The upper delta plain is where the deposits gather at the river.
An arcuate delta is a fan-shaped delta of which the Nile River is a good example. Many channels funnel water away from the main river drawing sediment to their mouths. The ambient (receiving) water is found not to be too deep with steady waves making the longshore current quite small. The shoreline is smooth due to the sediments being pushed back into the distributing channels.
Bird Foot Deltas
The Mississippi River's delta is a bird foot delta. Hardly any channels feed into the mouth of the delta. The sediment goes into the basin away from the channel mouths. The look of the bird foot comes from shallow shelves that unexpectedly become deeper for an extended and slender development. This type of delta is also considered a river-dominated delta because its shape depends upon what the river does and not much more.
Shaped like the tooth of the same name, cuspate deltas are similar to the Tiber River delta in Italy. There's only one channel that dumps into a level coastline where the waves butt heads with the fluvial output. The sediment, therefore, falls to either side of the mouth forming two shelves, one on either side of the mouth. The cuspate delta is also considered to be a wave-dominated delta, since the shape is brought forth most largely by the action of the marine waves in and out of the fluvial mouth.
France's Seine River offers an example of the estuarine delta, where the river empties into an elongated skinny estuary that fills with sediment within the coastline.
When there are large tidal ranges to deal with on the seaward side of a delta, the shape of the delta constantly reshapes at the very least twice a day. The current of the ebb tide is what determines the shape of the delta. These are largely seen in bay areas and estuaries that have a protected river mouth. Long tidal bars of sediment may be formed and at the junction of marine and river mouths you may see muds and sands cross-bedding without much wave action.