I believe the flood account and sumerian, accadian flood accounts share the same origin. A huge local flood that remained in the collective memory of those nations (not 2400 bce but older.
There are many more flood legends around the world. WT says it is because all humans come from Noah. I believe that those legends come from huge floods after the melting ofvthe last ice age 14000-8000 years ago. The sea level eas about 120metres below todays level. That gave an enormous amount of land to inhabit which is flooded now. There were maybe civilisations that we have never heard if.
In India for example in the gulf of cambay ruins were found deep below sea level. On the japanese island of yonaguni some there are structures deep under water that some scientists believe to be manmade.