The most common and most likely answer to this crossword clue is the 10 letter word BREAKWATER
I've seen this crossword clue in Financial Times
B
R
E
A
K
W
A
T
E
R
Buddy explains!
The straight part
We know that "A beach structure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a beach structure = breakwater.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does BREAKWATER mean?
BREAKWATER noun- A construction in or around a harbour designed to break the force of the sea and to provide shelter for vessels lying inside
- A low bulkhead across the forecastle deck of a ship which diverts water breaking over the bows into the scuppers
- On beaches: a wooden or concrete barrier, usually perpendicular to the shore, intended to prevent the movement of sand along a coast.