Frequently Asked Questions


FLOOD WARNING SYSTEM & INTERACTIVEMAP
   What is the goal of the Flood Warning System?
   What is the purpose of the Flood Warning System interactive map?
   How can I find historical rainfall or bayou/stream level information?
   How many gage stations make up the Flood Warning System?
   How can I find the gage station site closest to my home or work?
   Why does the Flood Control District use the “gage” spelling instead of “gauge”?

SYSTEM OPERATION
   How does the Flood Warning System work?
   Who pays for the Flood Warning System?
   How is the Flood Warning System maintained?
   How are gage station locations selected?
   How is the Flood Warning System data transmitted from a gage station to my computer?
   How is the accuracy of the Flood Warning System data verfied?
   What is a gage station?
   What is a sensor?
   What is a weather station?

DATA COLLECTION & REPORTING
   Who issues flood warnings?
   What is a partner agency?
   What happens during a storm?
   Who uses the data that has been collected?
   Why do some gages not show bayou/stream levels after a rainfall?
   Who do I contact if I have questions or see a damaged gage station?

FLOOD WARNING SYSTEM & INTERACTIVE MAP

What is the goal of the Flood Warning System?
The Harris County Flood Control District’s Flood Warning System measures rainfall amounts and monitors water levels in bayous and major streams on a real-time* basis to inform you of dangerous weather conditions.

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What is the purpose of the Flood Warning System interactive map?
The purpose of the Flood Warning System interactive map is to provide information collected by 133 rainfall and stream level gages in Harris County in a user-friendly format directly to you. This information is used by the Harris County Flood Control District and by Harris County’s Office of Homeland Security and Emergency Management to inform you of imminent and current flooding conditions along bayous and creeks. It also is used by the National Weather Service to assist in the issuing of flood watches and warnings. Accurate rainfall and bayou/stream level information help you and emergency management officials make critical decisions that ultimately can reduce the risk of property damage, injuries and loss of life. The Flood Control District urges you and your family to use this information and take the appropriate precautions during times of heavy rain and flooding. You are encouraged to monitor bayou/stream levels near your home, place of work and areas along your daily commute.

This website also provides information about historical rainfall and flooding events and about Harris County watersheds.

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How can I find historical rainfall or bayou/stream level information?
Historical rainfall and/or bayou/stream level information can be obtained from the interactive map by using the tool bar on the left side of the map page. Select the “Historical” tab under the “Rainfall Data” heading. From there, select the number of days and the date from which to count back, and click “Show Historical” to update the map and display that information. Information is available from the point when the gage station was installed to the present. The date a gage station was installed can be found on the top left of the gage station site information page.

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How many gage stations make up the Flood Warning System?
The system relies on 133 gage stations strategically placed on bridges that cross Harris County bayous and their tributaries.

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How can I find the gage station site closest to my home or work?
To view the gage station site that is closest to your home, business or other location, enter the street address and zip code in the address search field located to the left of the map and click the “Find” button. The map will zoom to that address and display a pin to confirm the address you entered. Once the address is found by the mapping tool, you can look for the closest gage station site to monitor bayou/stream levels.

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Why does the Flood Control District use the “gage” spelling instead of “gauge”?
While “gauge” can serve as an alternate spelling, the Harris County Flood Control District uses the “gage” spelling to be consistent with that commonly used in technical reports and by the United States Geological Survey (USGS). The Harris County Flood Control District and the USGS house data collection devices in the same shelter and use the same water-level measuring devices at approximately 46 gage station sites throughout Harris County.

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SYSTEM OPERATION

How does the Flood Warning System work?
When it begins to rain, data-collecting sensors at each gage station transmit rainfall amounts via radio frequency every time 0.04 inches of rain is measured by the sensor. Sensors that transmit bayou/stream levels report every 0.10-foot rise in water levels. The sensors transmit data to two primary repeaters located in the Huffman and Clodine areas. The repeaters then relay the data to primary and back-up base stations located at Houston TranStar and at the Harris County Appraisal District. The data is monitored daily by Harris County Flood Control District staff to ensure the gages are properly functioning and transmitting accurate data.

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Who pays for the Flood Warning System?
The Harris County Flood Control District funds the Flood Warning System and is responsible for its maintenance and operation.

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How is the Flood Warning System maintained?
The Flood Warning System requires extensive maintenance efforts because of the vulnerability of its equipment to the weather. The Harris County Flood Control District has five full-time staff members dedicated to the operation of the system. A rigorous preventive maintenance routine has been established to calibrate the rain gages and bayou/stream levels to +/- 3 percent. These extensive tests are conducted twice a year. In between testing, general maintenance is required, including surveying at gage stations, vegetation management, equipment and gage station upgrades; coordination with partner agencies; moving gage stations to accommodate construction activities; and testing field equipment to ensure accuracy.

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How are gage station locations selected?
Gage stations are strategically placed on bridges that cross Harris County bayous and their tributaries to maximize rainfall and bayou/stream level coverage. The gages help officials at the National Weather Service and local emergency managers make important decisions regarding public safety. Other agencies or the public may request gage stations to be installed at other locations. All requests are taken under advisement by the Harris County Flood Control District, but must meet the general standard of providing useful data to the Flood Warning System.

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How is Flood Warning System data transmitted from a gage station to my computer?
When it begins to rain, data-collecting sensors at each gage station transmit rainfall amounts via radio frequency every time 0.04 inches of rain is measured by the sensor. Sensors that transmit bayou/stream levels report every 0.10-foot rise in water levels. The sensors transmit data to two primary repeaters located in the Huffman and Clodine areas. The repeaters then relay the data to primary and back-up base stations located at Houston TranStar and at the Harris County Appraisal District. The data is monitored daily by Harris County Flood Control District staff to ensure the gages are properly functioning and transmitting accurate data.

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How is the accuracy of the Flood Warning System data verified?
The data reported by the Flood Warning System is checked for accuracy on a daily basis. A technician reviews the sensors’ data for inconsistent information and makes corrections as necessary. A large amount of inconsistent data coming from a specific sensor usually indicates that a site needs maintenance. In this case, a field technician is sent to the location to investigate and to repair the problem.

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What is a gage station?
Usually located on a bridge over a bayou, creek or other waterway, a gage station contains sensors that transmit valuable data during times of heavy rainfall and during tropical storms and hurricanes. The Harris County Flood Control District’s Flood Warning System relies on 133 gage stations. The majority of gage stations in Harris County measure rainfall amounts and water levels only. A gage station can use one of four real-time water-level measuring devices: bubbler, pressure transducer, radar or stilling well.

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What is a sensor?
A sensor is a data collection device that transmits data collected at gage stations at certain intervals, either as weather conditions and water levels change or at pre-determined points in time.  When it begins to rain, data-collecting sensors at each gage station transmit rainfall amounts via radio frequency every time 0.04 inches of rain is measured by the sensor. Sensors that transmit bayou/stream levels report every 0.10-foot rise in water levels. The sensors transmit data to two primary repeaters located in the Huffman and Clodine areas. The repeaters then relay the data to primary and back-up base stations located at Houston TranStar and at the Harris County Appraisal District. The data is monitored daily by Harris County Flood Control District staff to ensure the gages are properly functioning and transmitting accurate data. Gage station sensors also can measure: air temperature, barometric pressure, humidity, rainfall, road temperature, water level, wind speed and wind direction.

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What is a weather station?
A weather station is a gage station that measures weather conditions in addition to rainfall amounts and bayou/stream levels. Additional weather conditions that can be measured include: air temperature, barometric pressure, humidity, rainfall, road temperature, water levels, wind speed and wind direction. Some of the gage stations in Harris County may be considered weather stations. Sensor types for a weather station location are determined based on the need for particular weather data for that location. For example, working with the City of La Porte, the Harris County Flood Control District installed wind direction and wind speed sensors at existing gage stations to help support emergency response officials during chemical releases in that region of the county. The Flood Control District is responsible for seven weather stations located throughout the southeast portion of Harris County (Houston TranStar and the Reliant Stadium, city of Houston; Big Island Slough at Fairmont Parkway, La Porte; Little Cedar Bayou at 8th Street, La Porte; Sens Road just south of HWY 225, La Porte; Willowspring Creek at Fairmont Parkway, La Porte; Clear Creek at Hwy 146, Seabrook; Taylor Bayou at Shoreacres Drive, city of Shoreacres).

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DATA COLLECTION & REPORTING

Who issues flood warnings?
The National Weather Service has the sole responsibility for issuing regional flood warnings and advisories and issuing specific watershed flood warnings and advisories. The Harris County Flood Control District provides the rainfall and bayou/stream level information and closely coordinates with the National Weather Service to issue the proper warnings and advisories for Harris County to reduce the risk of property damage, injuries and loss of life. These advisories and warnings are disseminated using National Oceanic and Atmospheric Administration weather radio, the media, and local emergency operation centers.

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What is a partner agency?
In addition to the Harris County Flood Control District, several agencies in the region also operate and maintain flood warning systems. These agencies are collectively called the Regional Flood ALERT System and are referred to as “partners” in various areas on the Flood Warning System website. While each agency is responsible for its system’s maintenance, these partners use the radio frequencies that transmit data from rainfall and bayou/stream level gages to their local base stations or to Houston TranStar. Partner agencies include: Fort Bend County, the Harris County Toll Road Authority, the city of Houston, the Metropolitan Transit Authority of Harris County, the city of Pearland, the city of Sugar Land, the Texas Department of Transportation, and the Trinity River and San Jacinto River Authorities. Both the Flood Control District and our partners’ information are available to you on the interactive map.

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What happens during a storm?
During a storm, the Harris County Flood Control District has a group of dedicated staff members called the ALERT Team that monitors and responds to heavy rainfall and flooding. The role of the ALERT Team is very important, as gathering reliable data is needed to determine where flooding is occurring or is expected. During heavy rainfall, technicians on the ALERT Team monitor rainfall amounts and water levels in bayous and creeks and report that information to Harris County Office of Emergency Management officials and emergency mangers with other agencies. They also may be required to go directly to a gage station that is not reporting consistently or that is suspected to have erroneous data. If conditions allow, they may attempt to correct the issue or determine water levels using measuring tapes or by making visual observations. The proper maintenance of gages between weather events helps ensure consistent and accurate data during times of heavy rain.

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Who uses the data that has been collected?
The data collected is used by the Harris County Flood Control District and other agencies for numerous purposes. The most important use of the data is during times of excessive rainfall and flooding when local emergency managers and the National Weather Service issue warnings and advisories to the public. The information also is analyzed by the Flood Control District to develop post-flood reports. These reports detail the extent and impact of flooding, including an approximation of the number of structures inundated. In addition, the Flood Control District uses this information to perform engineering analyses for identifying locations of future projects as well as determining the effectiveness of its constructed projects. The River Forecast Center and private companies acquire the information for use in gage-adjusted radar rainfall, which uses the rainfall data to determine the accuracy of the National Weather Service’s radar.

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Why do some gages not show bayou/stream levels after a rainfall?
Not all gages are equipped to measure all changes in bayou/stream levels. The Flood Warning System has four types of real-time, water-level measuring devices. They include: bubbler, pressure transducer, radar and stilling well. The decision to use a particular device at a gage station site is based on how well the device is expected to function given the characteristics of a bayou or creek. For example, it is difficult to maintain a pressure transducer or a bubbler in a sandy bayou where silt can regularly plug the opening at the end of the device compared to a concrete-lined bayou where silt is less of a concern. In instances where erosion, silting or high amounts of debris are a significant hindrance, a radar or stilling well may be used and kept several feet above the normal water level to ensure successful operation. These devices will not report data until water levels in the bayou reach a certain height. When conditions are wet, most water-level measuring devices are in contact with the water, but during extended dry periods some of the devices can be 4- to 5-feet above the water.

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Who do I contact if I have questions or see a damaged gage station?
If you have questions about the Flood Warning System, you can contact the Harris County Flood Control District using the e-mail link on the map page or call our office at 713-684-4000.

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For information about flooding and flooding risks in Harris County, visit the Harris County Flood Control District at www.hcfcd.org.

*The data presented on this mapping tool and website may be delayed by approximately five minutes.

The Flood Warning System interactive map and website are for general information and educational purposes only. Their purpose is to provide information collected at gage stations, which monitor rainfall and water levels of streams and bayous as well as other weather information in the Harris County region. Use and interpretation of this data and information is the responsibility of the user. Neither the Harris County Flood Control District nor Harris County represents the data as 100 percent accurate. You should follow directions provided by emergency management officials when making decisions during flooding or other weather-related events.