What rhetorical techniques did Wu Feng Shui Liuli Hua use?

Metaphor.

The phrase "the windless water surface is slippery with glass" comes from "Picking Mulberries: A Short Boat on the West Lake" written by Ouyang Xiu in the Song Dynasty. The phrase "the windless water surface is smooth as glass" in this poem uses metaphorical rhetoric. The "windless water surface" is compared to "glazed smoothness", which vividly depicts the calmness and smoothness of the water surface, as if there is no wind, making the lake surface as smooth as colored glaze.