It's a valid spelling, around these parts, though. As well as elsewhere on this little island of mine. "Dike" is generally used in geology for natural formations, so I tend to use the alternative "Dyke" for a
man-madeartificial construction so as to differentiate. As long as I use it in context, I've got no problem. (Although, just like I'd not be able to use the N-word, I'll let those who identify with the term use it in
that context unless explicitly invited to.)
Although see the (to some, amusingly named)
Hag Dyke hostel where the latter spelling is used for a natural geography and
Scout Dike outwards-bounds place where I think (though I can't currently find proper references) it was named for a man-made construction. Literacy has settled such things so relatively recently, compared with the age of both the natural and man-made features involved. See also "Offa's Dyke" and "Wat's Dyke", among others, but "Scots' Dike" that seems to have been named comparatively recently, after rejecting the more 'fluid' or Dutch-inspired spellings such as "Dyik".
Interestingly, there was a Greek goddess known as "Dike", but that's just the accepted anglo-Latinesque spelling of the Greek original, and pronounced "Dikey" (just like "Nikey" is for the shoe brand), and as far as I can see has no reason to be connection, at least in relation to the more probably and more vulgar (or, indeed 'vulva') connotations towards the ditch version, directly or indirectly.
But, anyway, apologies if there was any offence. On the other hand, if it has caused no furore and I am not to be condemned to gaol due to its connexion with the arse-end of the English language, I'm happy if you're just bemused by all the colourfully Anglicised spellings that I can jemmy into the centre of my speech, as behoves my brand of speciality writing.
(See what I did there! And I'm gratified to find that my spill-chucker only complains about one of the above words, and that was the word "arse".
)