There are several synonyms for the word "floodproof" that can come in handy when speaking about flood prevention and management. Some of these synonyms include "waterproof," "water-resistant," "seepage-proof," "impervious to water," and "flood-resistant." Additionally, words like "safeguarded," "secure," and "protected" can also be used to describe something that is made to withstand flooding. Using synonyms such as these can help to broaden your vocabulary and add depth to your writing when discussing the topic of flood protection and prevention.