100-year flood

A "100-year flood" is a term used in hydrology to describe a flood event that has a 1% chance of occurring in any given year. This means that, statistically, such a flood might be expected to happen once every 100 years. The magnitude of these floods, along with 500-year and 1,000-year floods, is calculated by analyzing historical streamflow records. These calculations are crucial for the engineering design of water resource projects like dams and reservoirs, as well as other structures that could be impacted by severe flooding.1

Floods themselves are defined as a high-water stage where water overflows its banks onto normally dry land. While some floods, like the historical Nile River floods, were beneficial for soil enrichment, others, such as those along the Yangtze and Huang He rivers in China, have repeatedly caused disaster. Floods can result from heavy rainfall, ice jams, storm surges, or tsunamis.1