Heavy rain and waterlogging on event sites
Rain matters to an event in two places: the ground under the structures and the surfaces under people's feet. This guide sets out the Met Office definition of heavy rain and what MUTA and HSE say about each.
What counts as heavy rain
For rain other than showers, the Met Office classes rain as slight below 0.5mm an hour, moderate from 0.5 to 4mm an hour and heavy above 4mm an hour. The figures come from its fact sheet on water in the atmosphere.
Source: Met Office: National Meteorological Library fact sheet 3: Water in the atmosphere (archived copy)
Saturated ground and anchors
MUTA's Best Practice Guide says the pull an anchor stake can withstand depends on the type of soil, water penetration, the angle of the anchor and its depth.
For structures that stay up for longer, it says ground conditions can change with the weather. Firm soil or grass can become saturated and soft, so anchorage holdings may alter. It says they should be checked on the maintenance visits agreed between the contractor and the client.
It also says every upright should have a way to spread the load at its base so it does not sink on soft ground.
Source: MUTA: Best Practice Guide 2026
Water on fabric roofs
MUTA says roof panels should be tensioned enough to avoid ponding, where water collects on the roof.
Source: MUTA: Best Practice Guide 2026
Wet surfaces underfoot
HSE says that if rainwater gets onto a smooth surface inside or outside a building it may create a slip hazard. It notes that good entrance design, such as a canopy, can help.
Source: Health and Safety Executive: Slips and trips: environment
Surface water and flood warnings
GOV.UK says you cannot get flood warnings for surface water flooding, sometimes known as flash flooding. The Environment Agency's warnings cover rivers, the sea and groundwater, depending on the area. For surface water on your site, a heavy rain forecast is the closer signal. The flood warnings guide explains the official warnings.
Where a forecast fits
A forecast of heavy rain days ahead gives time to check anchors with your contractor and plan routes for people before the ground is wet. It does not replace a walk round the site on the day.
How Gustline helps
Gustline's heavy rain alert warns when forecast rain reaches your threshold, 4mm an hour unless you change it, which is the Met Office line for heavy rain. Beyond two days ahead the forecast comes in three hour steps, so Gustline compares the average hourly rate over each step. It comes in the same email and text as your wind alerts.
Gustline checks the Met Office site-specific forecast for the point you pin on the map, every six hours from a week out and every hour in the final three days. It compares the forecast gust with the rated limit you enter for each structure and checks the weather alerts you leave on for the event. When a level changes it emails and texts the people you choose. Every alert is logged with a timestamp.
Gustline is an early warning for planning. It does not replace checks on site on the day, the official warnings or your event's own plans.
Plans start at £19 for one event. A season pass is £99 a season and a year pass is £179 a year. It covers the UK only.
Set up alerts for your next eventSources
- Met Office: National Meteorological Library fact sheet 3: Water in the atmosphere (archived copy)
- MUTA: Best Practice Guide 2026
- Health and Safety Executive: Slips and trips: environment
- GOV.UK: Get flood warnings by text, phone or email
Last updated 4 October 2026.
Read next
- Flood warnings near an event site
What an Environment Agency flood alert, flood warning and severe flood warning mean for an event in England, what they leave out and where to sign up.
- Ice and frost on event sites
Air frost, ground frost and black ice from Met Office definitions, with HSE advice on gritting walkways and where a forecast fits.
- Wind limits for marquees and tents
A marquee's wind limit comes from its design certificate, not a general figure. What MUTA guidance says about design wind load and wind management plans.
- How to read a Met Office forecast for an event
What the Met Office forecast table means: wind speed and gust, chance of rain, visibility, hourly and three hourly steps and how accuracy drops with range.