Integrated Flood Observing and Warning Systems (IFLOWS)

Program history

IFLOWS network

How IFLOWS works

LinksIFLOW Gauge

 Have you ever seen one of these gadgets growing out of the ground in southwestern throughout northwestern Virginia?  It is about ten feet tall and one foot in diameter with an antenna and solar panel attached to it.  You can see it along rural roads, along mountaintop roads and hiking trails, and at some Soil and Water Conservation District dam sites.  This gadget is an IFLOWS monitoring rain gauge.  It contains a tipping mechanism (tipping bucket) at the top and in the lower two feet of the enclosed pipe buried in the ground is a radio transmitter.  Each tip of the tipping bucket measures 1 millimeter (0.04 inch) of rainfall.  At some sites a pressure transducer, a float or a sonic sensor is installed in streams or the normal pool area of reservoirs to measure the depth of water (in 0.10 feet precision) above the monitoring sensor.

Program History

IFLOWS had its early beginning after the severe flooding of 1977 along the borders of the tri-state area of Kentucky, Virginia and West Virginia.  Because of this disastrous event the National Weather Service developed the National Flash Flood Development Program in 1978.  The concept of the Integrated Flood and Warning System was initiated and has been developed extensively since then.  The goals of the IFLOWS Program are to substantially reduce the annual loss of life from flash floods, reduce property damage, and reduce disruption of commerce and human activities.  To develop the IFLOWS concept the National Weather Service began a joint effort with the above states in the Appalachian Region of the United States to undertake the establishment and development of a flash flood system to improve flood-warning capabilities in that region.

The system began as a prototype in 1980 in a 12-county pilot area using computers, communications, rainfall sensors and specialized software to monitor rainfall to provide early warning to the jurisdictions.  The pilot area was selected because of its susceptibility to flash flooding and its lack of existing flood warning systems and the availability of communications circuits to tie the tri-state area together.  The pilot program proved to be successful and has been through considerable development and expansion since then.

The NWS completed the Prototype system in 1981, and work began on expanding the system in the three original states and on developing IFLOWS in Pennsylvania and Tennessee.  The expansion was targeted to implement IFLOWS in approximately 120 counties in the multi-state area.

In 1985, Congress approved an amendment to a continuing resolution, which earmarked additional funding specifically for expansion of IFLOWS in areas hit by the devastating floods of November 4-5, 1985.  This area encompassed 29 new counties in West Virginia and numerous counties in Virginia and Pennsylvania, which were, declared disaster areas.  It was also expanded to include counties in North Carolina and New York with a history of serious flash flooding problems in the past.

While resource limitations have restricted additional expansion of direct NWS support for new IFLOWS installations, IFLOWS technology has now spread well beyond the seven original states.  Numerous communities, state, and federal agencies are now linked in a wide area communications network using this technology.  The IFLOWS network connects numerous flood-warning systems, and integrates and shares information from approximately 250 computers and 1500 sensors in 12 states as shown in the drawing to the right.

IFLOW states

The Virginia IFLOWS Network

In Virginia the IFLOWS program is a joint venture of the NWS, the Virginia Department of Emergency Management, and the 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 Services Coordinator.  The locality also provides a location for the computer and communications equipment (radio receivers and transmitters).  The local jurisdiction is also 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 western part of the state 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 that are maintained by VDEM.  Also in these 35 jurisdictions is an IFLOWS communications system that utilizes 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 available.

There are also about 30 read-only systems installed at various industries, private individuals, 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.  For instance a county can receive and store data from all the locations in Virginia, West Virginia, Kentucky, Tennessee, and North Carolina because of gateways set up between the other states.  In other words the system can operate as a stand-alone system or can integrate as many jurisdictions (computers) as the system operator desires.

The IFLOWS software also 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 on the Internet at the following address:

Questions about Virginia’s IFLOWS program can be directed to Mark Slauter at (804) 674-2405 or