There are technically two examples of metaphors in this poem.
(1) "Puts an arm of sand in the span of salt" is a metaphor because this isn't talking literally there isn't an actual arm of sand. This can also be classified as personification which is when you give human traits to a non human thing, like "the sun smiled down on us".
(2) "Wavelets Crumble" is a metaphor because wavelets cannot actually crumble I mean they're wavelets how can they do that.