The chiastic structure of the flood narrative suggests a single author. Yet the documentary hypothesis splits it into J and P components some of which are shorter than one verse.
Hello Spud
The structure of the Flood narrative suggests nothing of the kind - in fact, when the glaring contradictions are pointed out, and the sudden shifts of narrative, let alone the somewhat differing 'doublets' are noticed, it is a wonder that anyone who has read the text could think it had one single author.
There are many items I could bring to your attention, but a few notes should be enough. The entry of the families and animals is recorded twice, and in the 'Yahwist' narrative, the number of seven 'clean' pairs of animals is specified (because the author of this bit knew that Noah would later be sacrificing a few - and that would put an end to certain species at a stroke, if there were only one pair of each, as the Priestly narrative relates).
The Flood is also given quite different durations in the two combined accounts - forty days and forty nights we remember, but in the second account, 150 days are mentioned.
Furthermore, the structure of the cosmos related in each flood account is a direct mirror of the two accounts in Genesis 1 and 2 (you will probably know that the Priestly author is supposed to have written Genesis 1, whilst the Jahwist author wrote G2).
Following the analysis of the DH, if you split the text into the suggested Priestly and Jahwist accounts, you will find that each separate narrative tells a flowing, self-consistent story.
The short sentences which have been attributed to one author or the other do not detract from the main argument, which depends much more on large swathes of narrative.
Can't see the joins? They're much easier to spot than those on Donald Trump's wig!