Question

You are designing a house near a creek and are concerned about flooding. An expert tells you that the site is unlikely to suffer from headwater flooding but that you might want to raise the building or set it back from the creek because of the possibility of a backwater flood. What is the difference between these two types of flood?

Answer

A headwater flood is caused by precipitation directly into a basin. A backwater flood is caused by high stages on downstream outlets that prevent drainage from tributary basins or can even reverse the flow up the tributary. In the site in question, the collection area of the creek is probably small enough that flooding is unlikely from above (headwater flood). The creek, however, drains into another that could flood high enough to back up your creek to your house site (backwater flood).