Wednesday, March 22, 2023

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.  


  1. starting SERP: what is the sediment blocking a river from the ocean called there's a lot to digest…
    some terms to sift:
    fish in estuaries - looked at 'shoals & groyne' too:
    EPA info:
    " Estuaries provide habitat for about 68 percent of the U.S. commercial fish catch and 80 percent of recreational catch. Estuaries are also a major stopover point for migratory animals such as waterfowl."
    seems to be a lucky place for aquatic/fish life…

    a potential problem:
    what California river was most blocked at its delta
    no shortage of runoff this year:
    to the south:

  2. The name varies from place to place here in Australia, but the most common name is a bar. In some places they are called river bars, but in others this is only used for temporary sand islands that occur in the middle of a river. I've also head mouth bar, bar island, barrier island, lagoon wall. There is a town in NSW called Old Bar, which is where a major river was blocked from reaching the ocean years ago, but upstream work caused the mouth of the river to migrate.

  3. For your second question, I found a source that added another two terms: a delta shoal and an ICOLL (intermittently closed lagoons and lakes)
    This source indicate that while it often has deleterious effects on the population and diversity of fish species, some fish benefit and grow to a much larger size and that human intervention to open the bar may, in some cases, have detrimental effects in the estuary due to a sudden release of fresh water. However, another source:, suggested that for the longest river in Australia which is often intermittently blocked, that human intervention was beneficial.

  4. Hello Dr Russell!

    Very interesting and made me remember sometimes when in TV Shows I see something similar (I know it's not.) Maybe one day I can learn what that phenomenon is. It occurs in Hawaii.

    Related to Nature, curiously today learned about The Wallace's Line. I wonder if there are other similar.

    And out of topic but impressive:
    140 megapixel image of our Sun.


    About the Challenge it made me remember Estuaries but I don't remember exactly what they are. So I'll SRS!

    1. With [sediments block river passing],sediment%20is%20called%20overbank%20deposits.

      Deltas, river banks, and the bottom of waterfalls are common areas where sediment accumulates...Sediment created and deposited by glaciers is called moraine...In coffee: sediment called dregs.

      With [sediments block river passing to the sea]

      Essential to building barriers such as sandbars, dunes and marshes that protect coastal communities from storms and sea-level rise...Also mentions damn removed in California and what happened

    2. After reading Jon comment, searched [ River morphology] that links to Bar (

      In Spanish version names some bars (barras) in Mexico. I tried with Dr. Russell query [ Lista de barras] That didn't work. Barras are not what we're looking in the results. In English (bar) also didn't work to find a list with more famous bars (river related)

  5. speaking of terms…
    a "furphy" - (a whole other language)
    Narrung bund

  6. fwiw -

  7. still searching -
    why you don't go on the sandbar alone…
    Jenner/Russian River

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

    I knew this one one right off.

    It is called a bar or sand bar in this part of the world. Fast running water pushing sand and gravel along suddenly slows when it hits the ocean depths. When this happens the load of sand and gravel also stops and fall to the bottom. We have several enourmous piles this material left over from glacial melt times thousands of years ago. Just north a similar former bar is being mined for gravel to send to Los Angeles for use in concrete. So, no gravel piles in lower CA due to no Glacial melt water. A famous one is at the mouth of the Columbia River.
    Samuel Clements, a former Mississippi river boat pilot got his nickname from the constant need to measure the changing water depths for the river boat. Twain is two the Mark is the fathom 6feet mark on the measuring rope.

    It has different names in different languages.


  9. My next source was my 30 year old copy of Oceanography of the British Columbia Coast by Richard E Thomson.

    Pge 32 "A spit (or hook) is a beach with one end joined to the shore and the other end free where it terminates in a hook or recurve, Spits are most common on irregular coasts where they often grow across bay mouths and the entrances to rivers and extend them in the direction of the the littoral drift." They need constant feeding so they do not wash away.

    The processes are measured in years and decades; fishies have lots of generations to escape.

  10. Replies
    1. Thanks for the reminder; I have been there several times years ago

  11. Orca/Canada related…
    water language -

  12. city coastline - a swarm warning today… sand will adapt

  13. interesting images:

  14. the very controlled beach - 360 view Crane Cove Park
    no sandbar/spit there…

  15. more coast development - India Basin
    in the swarm zone

    "Why is it called India Basin?
    Image result for india basin san francisco
    The best guess is that India Basin is named for the ships from the India Rice Mill Company, which docked there in the 19th century. A more creative explanation has it that it was so named because water from the nearby spring would stay fresh until a ship reached India."

  16. feeling scrambled & shell-shocked…a change of pace… SF/sea related… a flight of fancy
    hard to crack
    Serghei Platanov
    a list
    symbols, language, reality check, spoof – Babylonokia
    Fabergé not withstanding…
    SF eggs
    a revisit by sRs… Farallon Islands
    which came first? the egg or the war… easier answer here
    npr – 49ers
    snippet:"The California murre (Uria aalge californica) lays a large and delicious egg which was a staple of the coastal north American diet long before the introduction of the domesticated chicken. The murre nested by the hundreds of thousands on the Farallon islands off the San Francisco coast."