The Collaborative International Dictionary of English v.0.48:

Shelfy \Shelf"y\, a.
   1. Abounding in shelves; full of dangerous shallows. "A
      shelfy coast." --Dryden.
      [1913 Webster]

   2. Full of strata of rock. [Obs.]
      [1913 Webster]

            The tillable fields are in some places . . . so
            shelfy that the corn hath much ado to fasten its
            root.                                 --Carew.
      [1913 Webster]

WordNet (r) 3.0 (2006):

shelfy
    adj 1: full of submerged reefs or sandbanks or shoals; "reefy
           shallows"; "shoaly waters" [syn: reefy, shelfy,
           shelvy, shoaly]