Glossary - Harris County Flood Education Mapping Tool

Glossary

# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

1 Percent (100-year) Flood – A 1 percent (100-year) flood, also known as the Base Flood, is a flooding event that has a 1 percent (1 in 100) chance of occurring in any given year at any given location. Statistically, a 1 percent (100-year) flood has a 26 percent chance of occurring during a 30-year period of time, which is equal to the duration of many home mortgages. Contrary to what the term suggests, a "100-year flood" is not a flood that occurs only once every 100 years. A "100-year flood" can occur multiple times in a century.

1 Percent (100-year) Floodplain – A 1 percent (100-year) floodplain, also known as a Special Flood Hazard Area on a Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM or floodplain map), is an area at risk for flooding from a bayou, creek or other waterway overflowing during a 1 percent (100-year) flood. Structures located in a 1 percent (100-year) floodplain have a minimum of a 1 percent chance of flooding in any given year. Statistically, structures located in a 1 percent (100-year) floodplain have a minimum of a 26 percent chance of flooding during a 30-year period of time, which is the duration of many home mortgages. And, the risk for flooding increases the closer a structure is to a bayou or a creek, assuming the structure is not elevated. A mapped 1 percent (100-year) floodplain is an area where land development is regulated by a city or a county.

1 Percent (100-year) Storm Surge – A 1 percent (100-year) storm surge is a storm surge that has a 1 percent (1 in 100) chance of occurring in any given year in a coastal area. In Harris County, a 1 percent (100-year) storm surge is generally 11 to 13 feet above sea level.

0.2 Percent (500-year) Flood – A 0.2 percent (500-year) flood is a flooding event that has a 0.2 percent (1 in 500) chance of occurring in any given year at any given location. Statistically, a 0.2 percent (500-year) flood has a 6 percent chance of occurring during a 30-year period of time, which is equal to the duration of many home mortgages. Contrary to what the term suggests, a "500-year flood" is not a flood that occurs only once every 500 years. A "500-year flood" can occur multiple times in a 500-year period of time.

0.2 Percent (500-year) Floodplain – A 0.2 percent (500-year) floodplain is an area at risk for flooding from a bayou, creek or other waterway overflowing during a 0.2 percent (500-year) flood. Structures located in a 0.2 percent (500-year) floodplain have a minimum of a 0.2 percent chance of flooding in any given year. Statistically, structures located in a 0.2 percent (500-year) floodplain have a minimum of a 6 percent chance of flooding during a 30-year period of time, which is the duration of many home mortgages. And, the risk for flooding increases the closer a structure is to a bayou or a creek, assuming the structure is not elevated.

Base Flood – The Base Flood is a flooding event that has a 1 percent chance of occurring in any given year at any given location. It also is known as a 1 percent (100-year) flood.

Base Flood Elevation – The Base Flood Elevation (BFE) is the level to which floodwater is anticipated to rise in a bayou or creek during the Base Flood, also known as a 1 percent (100-year) flood. The BFE is used by a city or a county to regulate land development in a mapped 1 percent (100-year) floodplain. The BFE is specifically used to determine the minimum elevation at which a structure’s lowest finished floor should be constructed.

Channel – A channel is a waterway through which stormwater moves or is directed. It is a generic term used by the Harris County Flood Control District in reference to bayous, creeks, small tributaries and some ditches. A channel can vary in shape and size and can be either natural or man-made. The Flood Education Mapping Tool differentiates between open and enclosed channels. An open channel is an in-ground channel, such as a bayou or a creek. An enclosed channel is typically underground and contained in large box culverts.

Coastal Floodplain – A coastal floodplain is an area at risk for flooding during a 1 percent (100-year) storm surge, which is the rise in sea water generated by a tropical storm or hurricane that is higher than the predicted normal high tide. Structures located in a coastal floodplain have a minimum of a 1 percent (1 in 100) chance of flooding from a storm surge in any given year. Statistically, structures in a coastal floodplain have a minimum of a 26 percent chance of flooding during a 30-year period of time, which is the duration of many home mortgages. In Harris County, a 1 percent (100-year) storm surge is generally 11 to 13 feet above sea level.

Elevation Certificate – An Elevation Certificate is an official record that certifies the elevation of the lowest finished floor, adjacent land or location of the mechanical equipment of a structure in relation to the Base Flood Elevation (BFE) for a structure located in a mapped 1 percent (100-year) floodplain. An Elevation Certificate may be used to support a reduction in the cost of flood insurance.

Flood Insurance Rate Map – A Flood Insurance Rate Map (FIRM or floodplain map) is a map produced by the Federal Emergency Management Agency and adopted by a city or a county. It is used to determine flood insurance rates and to assist in floodplain management and the regulation of new land development. 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 during a tropical storm or hurricane.

FIRM Panel – A FIRM panel is a section of a Flood Insurance Rate Map (FIRM or floodplain map). A FIRM is divided into numbered panels, which are determined by the land area being mapped. Each panel is produced with a scale of 1 inch = 1,000 feet. Harris County’s FIRM consists of 144 panels.

Flood Insurance Study – A Flood Insurance Study is a publication of the Federal Emergency Management Agency that documents an area’s flooding risks for a Flood Insurance Rate Map (FIRM or floodplain map). A Flood Insurance Study typically contains information about an area’s flooding history, flood profiles of studied flooding sources (bayous and creeks), and the engineering methods used to develop a FIRM.

Floodplain Administrator – A floodplain administrator is a government official charged with enforcing building codes and regulations for land development projects in a mapped floodplain. Local building codes and regulations are written in accordance with requirements of the Federal Emergency Management Agency and the National Flood Insurance Program. There are 35 floodplain administrators in Harris County. Thirty-four represent municipalities within Harris County’s boundaries, including the city of Houston, and one represents Harris County’s unincorporated areas.

Floodway – A floodway is an area within a 1 percent (100-year) floodplain closest to a bayou or creek where land development is regulated by a city or a county. It is the area where water flows most quickly and is most likely the deepest. Technically speaking, the floodway is the area needed to discharge or move the 1 percent (100-year) flood, or the Base Flood, downstream without causing the Base Flood Elevation to rise more than 1 foot.

Letter of Map Amendment – A Letter of Map Amendment is an official amendment, by letter, to a Federal Emergency Management Agency Flood Insurance Rate Map. A LOMA establishes a property’s location in relation to a mapped 1 percent (100-year) floodplain. A LOMA is usually issued because a structure has been inadvertently mapped in a 1 percent (100-year) floodplain or when its lowest finished floor is elevated above the Base Flood Elevation.

Letter of Map Revision – A letter of Map Revision is a modification, by letter, made to a Federal Emergency Management Agency Flood Insurance Rate Map generally based on changes that affect the topography of land and hydrologic or hydraulic characteristics of a flooding source, and thus result in the modification of floodplains, floodways or Base Flood Elevation.

National Flood Insurance Program – The National Flood Insurance Program (NFIP) is a program created by Congress in 1968 to help property owners protect themselves financially from flooding. The NFIP offers federally-backed flood insurance to homeowners, renters and business owners in participating cities and counties, such as the city of Houston and Harris County. Participating cities and counties agree to adopt and enforce ordinances that meet or exceed the Federal Emergency Management Agency's requirements to reduce the risk of flooding. Flood insurance rates are set by the federal government and do not vary among insurance agencies.

Ponding – Ponding is the collection of stormwater on streets or on undeveloped land that typically forms when rainfall occurs exceeding the design capacity of a street’s drainage system or exceeding the land’s ability to drain.

Special Flood Hazard Area – A Special Flood Hazard Area (SFHA) is an area on a Federal Emergency Management Agency Flood Insurance Rate Map that has a minimum of a 1 percent chance of flooding in any given year. Structures located in an SFHA, also known as a 1 percent (100-year) floodplain, are required to have flood insurance if the owners have federally-backed mortgages or if their mortgage lenders require it.

Storm Surge – Storm surge is the gradual rise in sea level generated by a tropical storm or hurricane that is higher than the predicted normal high tide. Storm surge tends to be highest along the immediate coastline, in the heads of bays, at the mouths of rivers and creeks, and within inlets where seawater is forced to rise vertically.

Watershed – A watershed is a geographical region that drains to a common bayou, creek or other waterway. There are 22 major watersheds in Harris County.