A floodplain is land made fertile by the very water that overruns it, so tradition reads it as hardship that leaves something good behind. It also stands for living close to strong feelings.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.