Here's how the new inundation flood mapping tool works

HOUSTON – A new tool showing inundation maps after bayous go out of banks has been unveiled by the Harris County Flood Control District.

The new mapping tool for the Harris County Flood Warning System displays data about areas of current bayou and channel flooding.

The flood control district said the tool "is provided to help residents and emergency management officials make critical decisions that may ultimately reduce the risk of property damage, injuries and loss of life."

Users can type in their address to monitor live inundation mapping during a flood event, however the results might be up to 15 minutes behind.

Historical data for the inundation maps goes back to 2015.

The new mapping tool does not show flooding from the following**:

• Channels and tributaries without gages
• Ponding, which may occur during or after intense rainfall when water gathers in low-lying areas, such as in streets when the capacity of the storm sewer is exceeded.
• Sheet flow, which occurs when intense local rainfall flows overland to reach a channel. Frequently, this conditions exists when water "ponds" in the streets deep enough to flood residences that are not even near a creek of bayou. The water will seek a path to the channel by flowing overland, flooding residences and other structures that are in that path.

How it works

• Go to www.harriscountyfws.org on your desktop or mobile device.
• The MAP VIEW OPTIONS section at the top left allows you to add inundation mapping and other features to the county map. (When there has been no rainfall, the inundation mapping feature will not be available.)
• Go to the ADDRESS SEARCH box in the lower left column and type your address.
• The map will zoom to the gage station nearest to your location of interest. The icon shows the amount of rainfall (in inches) received at that location in the past 24 hours.
• Click on the gage station icon for more detailed information.
• Other MAP VIEW OPTIONS allow you to add watershed boundaries, drainage channels and channel status icons to the county map. You can also change the setting in the RAINFALL DATA section to see rainfall during various time periods.
• An instructional video that shows how to use the entire Flood Warning System, including the new inundation mapping tool, is available on the HCFCD YouTube page here:

**Information from HCFCD: Inundation mapping is shown to a zoom level of 500 feet and above. The map depicts the current extent of flooding, but does not include water depth.  The mapping tool will only generate a new map if the gage data for water levels changes by one-half foot. Also, damage to gages during a flood may affect the accuracy of the flooding estimate and inundation mapping in the vicinity of the damaged gages.