Integrated Flood Observing and Warning Systems – IFLOWS

The Virginia IFLOWS Network

In Virginia, the IFLOWS program is a joint venture of the National Weather Service (NWS), VDEM, and local participating jurisdictions.

  • The NWS has provided program management at the national level, including funds for software development, communications design and capital equipment costs (computers, radio equipment, rain gages, etc).
  • The state provides a program manager and assistant manager to coordinate all activities between the NWS, the local jurisdictions and other state and federal agencies.  The state also provides the communications maintenance support and operations of the central computer.  The Virginia State Police Communications Division maintains all of the radio/microwave communications equipment and a private contractor maintains the rain gage equipment in the field.
  • Each participating local jurisdiction provides a flash flood coordinator, usually the Emergency Management Coordinator.  The locality also provides a location for the computer and communications equipment (radio receivers and transmitters).  The local jurisdiction is responsible for the most critical item in the system – the Emergency Response Plan – to deal with the expected flooding situation.  Without a well-planned response, the early warning of a potential flood disaster is useless.

In Virginia, IFLOWS is installed in 35 jurisdictions in the Blue Ridge Mountains and westward – from Lee County in southwestern Virginia to Warren County in the northwestern area of the state.  There are a total of 282 rain sensors and 80 stream sensors scattered over this area maintained by VDEM.  Also in these 35 jurisdictions is an IFLOWS communications system that uses VHF radio/microwave communications technology to carry a voice network.  This network consists of the 35 localities, the Virginia Operations Center, and the NWS offices in Virginia.  Dual and party line service is also available.

There are about 30 read-only systems installed at various industrial, private, educational and government locations.  These systems are not on the IFLOWS communications backbone; however, IFLOWS software is running on these systems and radio receivers intercept the backbone frequency and receive and store the data in the IFLOWS database running on the computer.  By moving inventory and equipment, millions of dollars of have been saved by industry that monitors the data routinely.

How IFLOWS Works

A rain gage consists of a ten-foot by one-foot diameter pipe enclosed on one end.  The pipe houses a screened funnel to collect rainfall, a tipping bucket that measures each millimeter or 0.04 inch of rain and a VHF radio transmitter to send the tip counter number and gage identifier to either a mountaintop receiver or repeater or to a county receiver/computer system.

Stream gages consist of a pressure transducer placed in the stream, gage house stilling basin or reservoir that measure the changes in water depth.  The depth changes are transmitted by VHF radio to a receiving computer system and the depth and time are recorded in the database.  Usually rain gages and stream gages are co-located at the same site, using only one transmitter to send the gage data readings.

In Virginia, the radio messages are received in real time at the county sites and passed on to a computer, which processes the signal into useful information and posts it to the computer’s IFLOWS database.  When polled by the central computer at the Virginia State Police Communications tower building the county computers send new data to the central site via the VSP microwave system.  The central site computer receives and posts the information in its database along with data from other states and at 15-minute intervals rebroadcasts the data to the IFLOWS world.  Counties not able to receive the data directly from the gages can receive and store distant data in their database for analysis.

The IFLOWS software monitors the data as it is received and issues audible warnings when thresholds are exceeded.  Percentages of the NWS Flash Flood Guidance and stream or reservoir depths can be set by the jurisdiction coordinator to be warning levels.  The NWS issues the guidance that is the amount of rainfall to begin small stream flooding in 1-hour, 6-hour, 12-hour and 24-hours.  Using these as upper values for warning levels the coordinator can set percentages for the levels of warning he/she desires.

IFLOWS data is available online.

Contact Daniel Bradway at (804) 897-9974 or for more information.



Be ready. Be willing to help.

Virginia Disaster Relief Fund