Baymouth bar

A small-scale model, but it's the same mechanism! Washoe Lake, Nevada. The "bay" is the mouth of another of the recent erosional channels feeding into the lake (http://www.ipernity.com/doc/289859/44442428) from the recent flooding. Now that the current is no longer flowing out the channel, it's been walled off from the main lake by sand deposited due to so-called "longshore drift." Unless wind-driven waves are coming into the shore _exactly_ perpendicularly (which is extremely unusual), the sand on the beach gets pushed along the shore in the direction of the non-perpendicular component of the waves, and where the direction of the shoreline bends abruptly, the sand is built out into the water. It can wall off inlets (as here) or build peninsulas, so-called "spits." So, we have here a model of shoreline processes that are very important in large bodies of waters, such as the ocean. We can thank the Washoe Zephyr, that howling orographic gale coming across the lake, for the demonstration!

The insets on the left show views of the inlet after the current had stopped flowing, but before the bar was deposited; that on the right shows the bar later after even more sand has been laid down.