SearchResearch Challenge (3/22/23): What do you call the sediment that blocks a river from flowing to the sea?

 If you wander along coastlines as I do, 
you'll eventually see this... 

... the place where a river runs to the sea. It's always a dramatic place--fresh water meets salt water, and wildlife often congregates due to the fish that hang out there.  It's common to see squadrons of pelicans or seals chasing after the fishy bounty at the river's mouth. 

As the pair of pictures above show, the thing about these places is that they are often open connections from the fresh water river to the sea, but sometimes, especially in winter, storms will rearrange the sand and close off the connection between the river and the ocean.  

In the top image, the Gualala River is blocked from running freely to the sea by an accumulation of sand.  The water is a beautiful blue, and forms a fairly large lake behind the barrier.  

But as you can see in the bottom image, sometimes that pile of sand is washed away, and the river is re-connected with the sea. 

If you look at many rivers (at least in California), sometimes they're open, sometimes they're closed.  From my observations over the years, the closures vary by time of year, but these rivers are open about half the time.  Here are a few rivers in northern California--you can see that some are open, while some are closed.  

Big River

Estero de San Antonio

Russian River

Salmon Creek

So I got curious about this and tried to do a bit of research, but immediately ran into a frequent problem for all online researchers:  What is this thing called?  I need some good search terms--what should I use?  How do I find them?

This is a super common problem in SearchResearch Challenges... it's incredibly handy to know the name of something before you start searching for it.  As you know, your searches will be much more effective if you know the right terms.  

Can you figure out what good search query terms might be? 

1. What is this pile-of-sand blocking the river called?  Are there any synonyms for this thing? 

2. If these rivers open and close intermittently, what is the effect on the fish population?  Have they evolved to expect this semi-random open/closing?  What happens to the poor fish when this happens? 

As always, I want to learn not just the answer, but WHAT your search process was?  How did you find the search terms that we need to get to the bottom of this Challenge mystery?  

Share your process! We all want to know!  

Keep searching.