The phrase does not appear to be a standard technical, academic, or scientific term in any major field such as geology, hydrology, or paper manufacturing.
In some regions, a "Big Wet" refers to a massive monsoon or flood event (common in Australian English). Research papers on the Australian "Big Wet" of 2010–2011 often discuss climate cycles like La Niña. mature big wet
If you can clarify the subject matter (e.g., science, art, or a specific event), I can help you find the relevant documentation or research. The phrase does not appear to be a