Complex sentence: In Dennery Quarter, flash floods affected about 500 households, among them 400 that had their houses flooded or severely damaged; several residences had to be evacuated, while some people were trapped in their homes.
Split into simpler sentences: In Dennery Quarter, flash floods affected about 500 households; among them, 400 had their houses flooded or severely damaged. Several residences had to be evacuated, and some people were trapped in their homes.