Mapped Floodplains – Areas delineated on a Federal Emergency Management Agency Flood Insurance Rate Map (FIRM or floodplain map) that are at risk for flooding from a bayou, creek or other waterway overflowing its banks during certain rainfall or storm-related events.

Floodway – A regulatory zone within a 1 percent (100-year) floodplain closest to a bayou or creek where land development is regulated by a city or a county.

1% (100-year) Floodplain – 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 and a minimum of a 26 percent chance of flooding during a 30-year period of time.

0.2% (500-year) Floodplain – 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 and a minimum of a 6 percent chance of flooding during a 30-year period of time.

1% (100-year) Coastal Floodplain – 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.

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

Ponding – 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. On this mapping tool, the shade of red indicates the depth of the water. Dark red indicates deep ponding and light red indicates shallow ponding.

Channels - Waterways 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. When identifying channels, the Flood Control District uses a combination of letters and numbers to help easily identify the location of a waterway. On this mapping tool, channels have been labeled with formal identification numbers used by the Flood Control District.

Open Channels – Channels that are open and visible.

Enclosed Channels – Channels that are enclosed in box culverts.

Harris County Boundary – A line shown on a map to indicate the boundary of Harris County, Texas. This mapping tool only shows mapped floodplains for areas within Harris County.

Only one of the following map view options can be selected at a time: Mapped Floodplains, Watersheds (color-coded) and Ponding.