A FIRM also does not show flooding risks from events greater than the magnitude of a 0.2 percent (500-year) flood, such as Tropical Storm Allison, which dropped unprecedented amounts of rain and far exceeded a 0.2 percent (500-year) flood in some parts of Harris County in 2001. Half or more of the flooding that occurs in Harris County falls into these two categories.

A FIRM does not identify risks from street flooding caused by roadside ditches and storm sewers exceeding their capacity or from sheet flow, which is water traveling over land to reach a bayou. While a FIRM is a good indicator of flooding risks from a bayou or creek overflowing during certain floods, it does not identify all flooding risks for Harris County, which receives an average of 48 inches (4 feet) of rain each year. Its purpose is to identify areas at risk for flooding from a bayou, creek or other waterway overflowing during 1 percent (100-year) and 0.2 percent (500-year) floods, and from coastal flooding related to storm surge from a tropical storm or hurricane. It is used to determine flood insurance rates and to assist in floodplain management and the regulation of land development. What is a Flood Insurance Rate Map and how do I use it?Ī Flood Insurance Rate Map (FIRM or floodplain map) is a map produced by the Federal Emergency Management Agency (FEMA) and adopted by a city or by a county. What is a Flood Insurance Rate Map and how do I use it? Back to Top.Floodplain Status/Floodplain Determinationįor questions pertaining to development and construction of or improvements to a property located in a floodplain, contact your local municipality or the Harris County Public Infrastructure Department’s Permit Office at (713) 956-3000 or Flood Insurance Rate Map (FIRM or floodplain map).Flood Insurance Rate Map (FIRM or floodplain map).Select one of the following to view Frequently Asked Questions and Answers related to that topic.

Define base flood elevation