Many beaches where erosion is a problem are protected by groins
Early ModE phonetic rendering of grine, var. of grinde < ME grynde, prob. < OE, abyss, in sense “depression” (akin to grund, GROUND1)6
1 the hollow or fold where the abdomen joins either thigh
2 Archit.
a) the sharp, curved edge formed at the junction of two intersecting vaults b) the rib of wood, stone, etc. covering this edge (see VAULT1, illus.)
3 a strong, low sea wall built at a right angle to the coast to reduce shoreline erosion, esp. of a beach
to build or provide with groins

groin - 1592, from M.E. grynde "groin" (14c.), originally
"depression in the ground," from P.Gmc. *grundu; altered
16c. by influence of loin. The harbor structure groin is a
different word, from obsolete groin "pig's snout" (because it
was thought to look like one), from O.Fr. groin, from L.
grunnire "grunt." :

It never made any sense to me to think of the structures being in any way related to
the anatomoical term. And etymology site say it is a different word.