Almost the last talk at the EnvSciCnf this week came from the Geological Survey of Ireland GSI, one of Ireland's most productive government quangos. It was a report on the 400 examples of 'groundwater flooding'. This is when water comes blurfing out of the ground instead of either falling from the sky or travelling by beck rill stream and river through on its way to the sea. They only occur if the underlying rock is super soluble limestone karst: the water dissolves the calcium carbonate CaCO3 so that it becomes a complex network of sub-surface fissures. Given several thousand years, the fissures grow into interconnected tunnels and caves like Mitchelstown. Limestone cave-systems are thus always connected with and by water: as my pal Roy found in his near-death experience in Sleet's Gill. Groundwater flooding is when, hours or days after a good spill of rain, the underground network fills up and spills out of the top to flood the landscape. In Ireland these temporary lakes are called turloughs and they look like this:
Catalonia> of the GSI is The Effective in project GWFlood tasked to map the turloughs in space and time, so that all the stake-holders have a good idea about when and where and how deep water will appear. We have a pretty good idea of the location of all the [N=400] places where a turlough has ever appeared, but some of these locations are up a rough bohereen in Co. Roscommon and [so] there is no continuous record of their ups and downs and disappearance. There are two main techniques
- Put a sufficiently tall pillar in the lowest part of the local landscape. Incorporate an electronic dip-stick in the bottom and a radio-telemetry beamer on the top and an hourly report of water-level can be captured in GSI head office.
- Satellite mapping with LiDAR [prev] and SAR - synthetic aperture radar.
Why does it matter? Continuous data streaming of depth and area from groundwater flooding can help planners to determine where NOT to allow building to address Ireland's housing crisis. Because GW flooding involves landscape with no surface escape path for the flood-water, turloughs tend to hang around for a long time. Several families were unable to drive to-fro their homes for weeks after the "100-year floods" of Jan 2015. With climate change, you can bet your sweet bippy that 1000 year floods are now 100 year floods and 100 year floods will come more frequently. Cross-referencing the rainfall data with the flood-rise data allows a much wider demographic to plan their lives so that the car is on the right side of the turlough as if spreads across the bohereen . . . and go and buy a dinghy next time ALDI has one on Special.