If it helps, which it may not, the Japanese definition of a 名詞 (めいし), which is to say a noun, is:
a complete freestanding word (i.e. not something that only appears attached to another word, like a particle or an auxiliary verb)
which doesn’t have an ending that changes (i.e. not a verb or an i-adjective)
which can be the subject of a sentence (something you can mark with が)
The 50,000 foot view of relative clauses in Japanese is that they are a little mini sentence (ending in a verb) that goes in front of the word you modify. The mini sentence has to be correct Japanese in the same way as a main sentence does. So because 溢れてがある isn’t a grammatical main sentence, it doesn’t work as a relative clause either.
at 50,000 ft I skip some of the detail like the “can mark subject with のif you like” that @Voi notes ↩︎