Sentence:  The last tall son of Lot and Bellicent, / And tallest, Gareth, in a showerful spring / Stared at the <WSD>spate</WSD>. A slender-shafted Pine / Lost footing, fell, and so was whirled away. 
Meaning of the word marked with <WSD> tags:  A river flood; an overflow or inundation.