Ogunquit has one of Maine’s loveliest sandy beaches (to distinguish it from some pebble sites we frequent, especially). It’s more than a mile long facing the Atlantic, with house-free dunes behind it.
One corner, near the parking lot, is bordered by the Ogunquit River, which is fun to float in, as long as you avoid the whirlpool.
That end also has a lovely large apron of sand at low tide, and unsuspecting visitors often carry their towels, folding chairs, bags and coolers right out to the edge of the water, establish camp, and head off into the surf. While they’re at play, though, the tide turns quickly, submerging much of the apron within minutes, generally approaching the camp from behind. You should see their faces as they suddenly recognize the catastrophe at hand and desperately try to retrieve their floating debris from the quicksilver waters. Their chairs, coolers, towels and blankets, even shoes are all heading out to sea.
Soon, most of the beach on that end is under water. Remember, the level changes more than a foot every hour … and sometimes it’s closer to two.
The veterans, in contrast, set themselves up much higher, against the rocky base of the parking lot itself.
Follow their example if you go. Or watch out.
Jnana's Red Barn 
Sounds lovely – and lively!
One of my nearby Pacific beaches is faced by 100 foot high bluffs. Unlike Oginquit, these are encrusted with houses, eagerly poised at the edge to get the best view. Sadly, the bluffs have been collapsing for hundreds or thousands of years. So, our unwitting visitors have more challenging adventures than chasing coolers. Ignoring signs about crumbling cliffs, they cluster between fallen rocks at the base. Periodically, someone doesn’t hear the avalanche in time. So if you visit San Diego beaches, heed the signs.
We have similar problems, especially on parts of Cape Cod. You can’t argue with the ocean, now, can you?
It’s very true. The ocean abides, while our arguments fade away.
we have bays in the UK that do a similar thing, in fact there are some beaches that are inaccessible during high tide