noun
bridge pillar; bridge pile
Refers to the vertical supports driven into the riverbed or ground to hold up a bridge. A technical or descriptive term.
古い橋杭が川底に残っている。
Old bridge pillars remain in the riverbed.
橋脚 is the more common modern term for a bridge pier or support, while 橋杭 specifically suggests wooden piles or stakes.
Compound of 橋 (はし, 'bridge') and 杭/杙 (くい, 'stake, pile').