A UCD researcher is using radar to try to predict the locations where floods caused by heavy rains might arise, writes Dick Ahlstrom
More frequent flooding seems an inevitable consequence of our changing climate so research efforts are underway to find ways to predict floods before the water starts flowing.
One such project led by University College Dublin's Dr Michael Bruen involves using radar data to provide flood forecasting hours before the first raindrops fall.
Met Éireann runs radar systems at Dublin and Shannon airports to track approaching storms and measure rainfall. Bruen wants to use the radar data in conjunction with mathematical models of specific river catchments to give early warnings if a flood is likely to occur.
"It is something I have been looking at for the past three or four years," says Bruen who is director of the Centre for Water Resource Research within UCD's Department of Architecture, Landscape and Civil Engineering.
The centre involves the work of five core academic staff and 16 to 17 PhD students and post doctoral researchers, he says.
This new radar project received funding under Science Foundation Ireland's Research Frontiers Programme to develop an automated flood forecasting system. It will support two full time researchers for up to three years.
Bruen studied the impact of "Hurricane Charlie" which arrived in 1986 and caused major flooding of the Dodder in Dublin and the Dargle in Bray, with the latter causing €23 million worth of damage.
"Floods in small river catchments are quite different from floods say in the Shannon," says Bruen. "They happen much more quickly. You only have three to four hours to react before the flood hits you."
Small rivers flood quickly "when the volume of rain overwhelms the capacity of the soil to absorb the water", he explains. This happens very rapidly on small, hilly catchments, shunting large amounts of water down narrow water courses to affect low-lying areas and causing rivers to flood.
Large rivers and their correspondingly large catchments respond much more slowly, with large volumes of water building up to cause a flood. It then takes some time for all of the extra rainfall to flow out of the system and the waters to recede.
There are two ways to get information of an impending flood, rain gauges that relay rainfall data via radio link, or conventional radar. The gauges are highly accurate but only give information at a point location, he says.
Radar gives approximate rainfall across an entire river catchment but there is the issue of "ground truth", achieving an accurate interpretation of rainfall on the ground from radar signals that are subject to distortion.
"If you want to warn people you need this information from some telemetry source and I have been looking at radar," he says. "It is quite a complex problem."
Radar tells you were the rain is falling and how much, "but it is still only what is falling now". He wants to anticipate flooding, and achieving this involves combining the predictive capacity of radar to read approaching storms with models of how river catchments large or small will respond to a given amount of rain falling over a given amount of time.
Existing radar systems were not designed to give Bruen the information he seeks so he and his team will have to develop new ways to interpret the radar data stream. He will also have to cope with the slow radar "cycle", with new images taken only every 15 minutes.
The catchment modelling will be less of a problem given he is a hydrologist and has lots of experience in anticipating how a river catchment will respond to rainfall. It is still early days and initial work is along the lines of a "proof of concept", he says.
The plan is to develop predictive systems for three towns under Dublin's radar system, with the three yet to be selected. "If we can show this works then we can look at each town in the country to develop flood warning systems," says Bruen. "My feeling is it will work for some catchments but not for others. It possibly might be better for flat catchments rather than mountainous catchments."
If the system does give good predictive warning of impending floods, there may be justification for investing in more radar systems, he says. These cost about €100,000 to set up and run, but may be worth it to protect large towns that are at risk of floods such as Fermoy and Clonmel.
The key is advanced warning, he says. It can take 12 to 16 hours to put up flood barricades. "It could be that radar will give that extra time."