flooded area
例如这句国外网站上的报道：
A local resident navigates his boat in a flooded area in Luozhen Town of Fuzhou.
一位当地居民在抚州罗针镇的洪灾区驾驶着自己的小船.
LS说的flood-stricken area确实很常用,另外还有flood-hit area.