Photo: Kenneth Allen · CC BY-SA 2.0Johnstown faces few natural hazards: low radon, steady ground and few homes low by big water
With an estimated 1.2% of homes above the radon reference level, among the lower shares, Johnstown grades A− for hazard risk. Flood counts only against a town, so its share of low-lying homes earns it no credit: radon and landslide ground set the grade.
What stands out about Johnstown’s hazards
From the EPA’s radon map, Geological Survey Ireland’s landslide map, the OPW’s flood relief schemes and our estimate of low-lying homes, below.
What Johnstown faces
Each hazard against its own yardstick; meters run from low to high on that yardstick.
Low-lying homes
Radon
Landslides
Ground heights
Johnstown grades A− for hazard risk
Radon, landslide ground and low-lying homes, each against Irish towns, then averaged.
Each figure is placed among Irish towns of 1,000 or more people; the grade averages the three, so a better place on each is a better grade.
Flood counts only against a town, never for it: Johnstown’s share of low-lying homes would have raised its grade, so it isn’t counted, and radon and landslide ground set it.
Less sure: The low-lying figure is our estimate from ground heights and the river map, not an official flood map. It can show a town is low-lying; it can’t show a town is safe.
Few of Johnstown’s homes stand low by a big river, lake or the sea
Low-lying homes, a TownRatings estimate from OPW and Geological Survey Ireland LiDAR ground heights and the EPA’s river map: not an official flood map. Smaller streams, drains and groundwater aren’t in this measure, so a low figure doesn’t mean a town never floods.
Share of each town’s homes standing low by big water, for the towns measured in detail. 43% have none; Johnstown has more than 21% of them.
Low-lying homes across County Kildare’s towns · 12 towns measured in detail
Homes: OpenStreetMap buildings of 30 m² or more, not tagged as non-residential, in the town’s Census 2022 Small Areas. Heights: GSI Open Topographic Data LiDAR (OPW, TII and GSI surveys). Water: EPA river network (rivers of Strahler order 5 or more), lakes, estuaries and coastal waters.
December 2025 brought the River Morell’s highest day at Tipper since 2017
Each winter’s highest level (October to September) at the OPW’s Tipper gauge, 2.5 km from Johnstown on the same river, since 2017, in metres above the gauge’s zero. Nine days in ten it runs between 0.16 m and 0.31 m.
- 9 December 20250.38 m
- 1 December 20250.38 m
- 9 February 20200.38 m
- 12 November 20250.38 m
- 1 March 20240.37 m
- 21 July 20250.36 m
Since 2017 the River Morell has run above its usual top on 267 days, most of them in the winters of 2025–26 and 2022–23.
Measured by its highest day, last winter (2025–26) was the highest of the 9 on record here.
Source: OPW Hydro-Data (waterlevel.ie/hydro-data), Tipper gauge (station 09107): daily maximum and mean levels, inspected and provisional data. The usual range is the 5th to 95th percentile of daily means, worked out by TownRatings. Live levels are on waterlevel.ie.
Weather and flood warnings for Johnstown
Where to see the warnings in force, and what this page can’t count.
Met Éireann issues yellow, orange and red warnings for rain, wind and coastal flooding county by county; Johnstown is covered by County Kildare’s.
| Warning | What Met Éireann means by it |
|---|---|
| Yellow | Weather that isn’t unusual but can be dangerous in places: be aware. |
| Orange | Infrequent, dangerous weather that can put people and property at risk: be prepared. |
| Red | Rare, extremely dangerous weather: take action to protect yourself and your property. |
Met Éireann doesn’t publish an open archive of past warnings, so how often warnings have covered Johnstown can’t be counted here.
No OPW flood relief scheme protects Johnstown
The Office of Public Works’ completed flood relief schemes and the areas each one benefits (OPW open data, CC BY 4.0).
None of the OPW’s completed flood relief schemes has a benefiting area that takes in Johnstown’s homes. The OPW builds schemes where the risk to homes is greatest, so most towns have none.
In County Kildare, an OPW scheme also protects part of Celbridge.
| Town | Scheme | Designed for | Homes behind it | Away |
|---|---|---|---|---|
| Celbridge Kildare | Shinkeen Stream (Hazelhatch) Flood Relief Scheme | 1 in 100 | 2.6% | 13 km |
| Clonsilla Dublin | River Tolka (Clonee and Dunboyne) Scheme | 1 in 100 | 0.5% | 22 km |
| Dunboyne Meath | River Tolka (Clonee and Dunboyne) Scheme | 1 in 100 | 14% | 23 km |
| Clonee Meath | River Tolka (Clonee and Dunboyne) Scheme | 1 in 100 | 57% | 23 km |
| Mulhuddart Dublin | River Tolka (Fingal) Flood Relief Scheme | 1 in 100 | under 0.1% | 24 km |
| Dublin Dublin | River Dodder (Tidal) | 1 in 50 | 1.9% | 25 km |
No home in Johnstown stands on landslide-prone ground
Geological Survey Ireland’s landslide susceptibility map (1:50,000), read at every home.
Homes on ground rated high or moderately high
Johnstown is among the 64% of Irish towns with no home on such ground.
GSI rates ground from low to high by its slope, soil and rock. Most Irish landslides are on steep upland slopes and peat after heavy rain; a town on flat ground has almost none.
High means the ground could slide under the right conditions, such as days of heavy rain on a steep, wet slope; it isn’t a forecast that it will.
GSI landslide susceptibility, high and moderately high classes, share of the town’s homes on mapped ground (CC BY 4.0).
An estimated 1.2% of Johnstown’s homes are above the radon reference level
The EPA’s radon map: for each 10 km square, the estimated share of homes above the national reference level of 200 Bq/m³.
A square where 10% or more of homes are estimated above the reference level is a High Radon Area; 0% of Johnstown’s homes are in one. The map is an estimate by area: two neighbouring houses can differ a lot.
A test is the only way to know a home’s level: two detectors, left for three months in a living room and a bedroom.
EPA radon map of Ireland (10 km grid), averaged over the town’s homes (CC BY 4.0).
10 EPA-licensed sites within 5 km of Johnstown’s centre, none inside it
Factories, farms, power plants and waste sites that hold an EPA licence for their emissions, in Johnstown and around its centre.
| Site | Licence and activity | Away |
|---|---|---|
| Trimite Truecoat Limited | IPC licence | 1.3 km |
| Kerdiffstown | Waste licence | 1.3 km |
| Kildare County Council | Industrial Emissions licence · waste | 1.3 km |
| Dennison Trailers Unlimited Company | IPC licence | 1.3 km |
| Arrow Group | Industrial Emissions licence · food and drink | 1.6 km |
| Birds Eye Ireland Limited | Industrial Emissions licence · food and drink | 2.3 km |
| Arthurstown Landfill | Waste licence | 3.4 km |
| Boran Plastic Packaging Limited | IPC licence | 3.5 km |
| Activity | Sites |
|---|---|
| Waste | 7 |
| Not classed in the register | 5 |
| Food and drink | 2 |
| Wood, paper and textiles | 1 |
| Chemicals | 1 |
Within 5 km: 4 under Industrial Emissions licences, 3 under older IPC licences and 3 waste facilities.
An EPA licence sets what a site may release to air, water and land; it doesn’t mark the site as an accident hazard.
Sites holding dangerous substances in bulk come under the COMAH (Seveso) rules, but the HSA’s list of them has no open licence, so upper- and lower-tier sites aren’t counted here.
Source: EPA registers of Industrial Emissions, IPC and waste licences, sites licensed on 31 October 2026; distances in a straight line from the town’s centre.
Hazards in the places around Johnstown
Low-lying homes, radon and landslide ground, town by town.
Of the places around Johnstown, Clane has the most homes standing low by big water (32%), 8.2 km away.
A dash under Low-lying: not measured there (too few homes with detailed ground heights), not none.
Get ready for what Johnstown faces
What to do, and what to ask before you move.
- Never walk or drive through floodwater: 30 cm of moving water can float a car.
- Move valuables, papers and medicines upstairs.
- Turn off gas, electricity and water if you’re told to.
- Test over three months, in a living room and a bedroom.
- Above 200 Bq/m³, a small sump and fan usually fixes it.
- The EPA sells radon test kits at radon.ie and lists registered contractors who fix high readings.
- Bring in or tie down bins, trampolines and anything the wind can lift.
- Keep away from coastal paths and piers while an orange or red warning is in force.
- Charge phones and keep a torch: fallen lines are the commonest storm damage.
- After the storm, report a fallen line to ESB Networks and keep well clear of it.
- Ask whether the home has ever flooded, and get a buildings insurance quote before you commit: flood cover isn’t always offered.
- Ask the seller or landlord for a radon test result, or test in your first months there.
- Check the address on floodinfo.ie: the OPW’s flood maps and its record of past floods.
What this data can and can’t tell you
- An estimate, not a flood map. Low-lying homes is a TownRatings modelling step: each home’s ground height from LiDAR, against the level of the nearest big river (Strahler order 5 or more), lake or estuary within 1 km, or the sea within 2 km. A home within 5 m of the water’s level, or below 4 m near the sea, counts.
- Flood counts only one way. A high share of low-lying homes lowers the Hazard risk Grade; a low share never raises it, because defences, small streams, culverts, groundwater and flash floods don’t show in ground heights. Below the national median a town scores as the median.
- Defences aren’t counted. Flood defences aren’t taken off: the OPW scheme that protects the most homes is shown instead, with its design standard.
- Measured where the heights are detailed. A town is measured, and counted, only where 80% of its homes stand on LiDAR heights. Elsewhere the page says flooding isn’t measured, never that the town is dry.
- Radon is an estimate by area. The EPA’s radon map gives the estimated share of homes above 200 Bq/m³ for each 10 km square, averaged here over the town’s homes. It says where to test, not what one house holds.
- The sea is measured by height. Homes count as low by the sea when their ground is under 4 m and within 2 km of coastal or estuary water; waves, surges and erosion aren’t modelled.
- Landslide ground is a map of where slides could start. GSI’s susceptibility map rates the ground itself; it doesn’t record past slides or say when one will happen.
- Bathing water is rated season by season. The EPA classes each identified bathing water from four seasons of samples; a rating says how clean the water has been, not how safe it is to swim.
- One town, many streets. Risk is street by street. Check a specific address on floodinfo.ie before you buy or rent.
Check any address against the OPW’s official flood maps on floodinfo.ie
Questions about flooding and hazards in Johnstown
Does Johnstown flood?
Smaller streams, drains and groundwater aren’t in that measure, so it doesn’t mean the town never floods. For a single address, the OPW’s official flood maps and past floods are on floodinfo.ie.
Is radon a problem in Johnstown?
The EPA’s map estimates that about 1.2% of homes around Johnstown are above the radon reference level of 200 Bq/m³: a lower share than in 81% of Irish towns. 0% of its homes are in a High Radon Area. The only way to know a house is a three-month test.
Is Johnstown at risk of landslides?
No home in Johnstown stands on ground rated high or moderately high for landslides.
Is Johnstown at risk from the sea?
None of Johnstown’s homes stands below 4 m within 2 km of the sea, so the sea plays no part in its share of low-lying homes; 0% stand low by rivers, lakes and estuaries.
How does Johnstown compare with the places around it?
Radon estimates around Johnstown run from 1.2% in Kill to 11% in Blessington; Johnstown’s own is 1.2%. Among the places measured in detail, Clane has the largest share of homes standing low (32%).
How is Johnstown’s Hazard risk Grade worked out?
Johnstown grades A−: radon, landslide ground and low-lying homes are each placed among Irish towns, and the grade averages them.
Flood: TownRatings’ estimate from ground heights, not an official flood map. Contains Irish Public Sector Data (Geological Survey Ireland, the Office of Public Works and the EPA) licensed under CC BY 4.0; Copernicus DEM © DLR e.V. and © Airbus, provided under COPERNICUS by the EU and ESA; © OpenStreetMap contributors. Radon and bathing water: EPA (CC BY 4.0). Landslide susceptibility: Geological Survey Ireland (CC BY 4.0).
Sources: low-lying homes: TownRatings’ estimate from GSI and OPW LiDAR, Copernicus GLO-30 and the EPA river network · radon: EPA radon map · landslides: GSI landslide susceptibility · river levels: OPW Hydro-Data (waterlevel.ie/hydro-data) · industrial sites: EPA licence registers · the grade: TownRatings, from these figures. Under Creative Commons Attribution 4.0 (CC BY 4.0).
Contains Central Statistics Office (CSO) data, Census 2022, and Tailte Éireann boundaries (CSO Urban Areas, Small Areas, local electoral areas, constituencies), under Creative Commons Attribution 4.0 (CC BY 4.0).