Definition of "pierhead"

It came floating like a tethered cloud past the little white toy-like lighthouse at the pierhead.

1976, Angela Carter, “My Father's House”, in Shaking a Leg, Vintage, published 2013, page 21

Here on Papay folk will speak slowly and sympathetically in a one-to-one conversation with a 'soothmoother', but if you're on the fringes of a pierhead debate about the price of cattle or the weather, then you'll soon be submerged beneath a fast-flowing terminological tidal wave.

1996, Jim Hewitson, Clinging to the Edge: Journals from an Orkney Island, page 41