“It’s barely there” does not mean the same as “it’s barley there”. The former means that something scarcely exists. The latter is pointing out a plant or grain.
Monday Muddle: barely, barley
barely: (adverb) hardly; scarcely; by a very little; sparsely; almost imperceptibly barley: (noun) a grain used for food and in the making of beer; the plant from which the grain is harvested