Is Chesterton really saying that such things as floods are unimportant? What reason does he give for saying that the floods could be "accepted and enjoyed poetically"?

Chesterton poetic expression can be understood from the prism that no situation is good or bad but how our minds and the person in question perceive it will determine ones reaction to it.

Events occur, some see it as opportunity while others see it as destruction and a curse.

The flooding in was a destruction to business, home and properties but on the other hand it created opportunity to study the flood pattern in the city and proffer a lasting solution to it.