Site conditions: flood, ground and weather

The Site conditions block reads three desk-study facts about an event site: how much of each zone sits in a mapped flood area, what the soil is likely to do in wet weather, and the typical weather in the event’s month. Each reading names its source and date and says plainly what it does not cover. It is a starting point for the event safety plan — never a flood risk assessment, a site investigation or a weather forecast.

What Fetch site data reads

The block sits in the event sidebar under 4 · Event. ✅ Checks ▸ ⛰️ Site conditions in the palette and ⛰️ Site conditions in the sidebar's 11 · Analysis & Simulation both bring it into view, opening the side panel and unfolding 4 · Event if they are closed. Opening it reads nothing: before the first fetch it says "Site data not fetched yet", and without a boundary or a map location it says which is missing. Press Fetch site data and our server is asked three things:

• Flood — for the box around the site boundary (with a 50 m margin on every side), the national flood map of each nation that box touches. The server works out the nations itself, from the ONS countries boundary (and, only for a box the boundary places in no nation, the nearest postcode within 2 km via postcodes.io). Nothing about the nation is taken from your browser.
• Ground — the soil at the centre of the site boundary.
• Typical weather — the 1991–2020 monthly averages for the series that covers the site, all twelve months at once, at the same point. Because all twelve come back together, changing the event date shows a different month without asking again.

It needs a closed site boundary and a map location; without them the readings say "site boundary not drawn" or "no map location" instead. The flood check covers sites up to 5 km a side — the national services return whole flood outlines, so a bigger box would mean an enormous download. A larger site reads "flood not checked: the site is over 5 km a side".

The fetch is one step in the undo history: the per-zone shares, the nations read and the soil reading are saved with the design, so the appendix prints the same figures offline and on another device. The flood outlines themselves are not saved. When a saved design is reopened, the flood map is read again once, quietly, so the shares can follow a zone you move — and if that read fails, a zone moved since the fetch says "flood shares stale" rather than showing an out-of-date share as current. Review and share links never fetch; they show the saved readings.

After the site moves more than 1,000 m, or grows past the box that was fetched, the button reads Fetch again and says why. Nothing re-fetches on its own beyond that one quiet re-read.

Flood: one national map per nation

Each nation publishes its own flood map, and their zones mean different things. Every output names the source that judged each zone and prints that nation's definition beside its shares; the nations are never pooled into one standard.

The SEPA mapping is ours. A SEPA likelihood band is not an English flood zone. To give Scottish sites the same checks, High or Medium likelihood takes the higher role and Low the lower; every Scottish line says "(our mapping)".

What the shares mean

For every event zone and car park the block shows the share in the higher zone (Flood Zone 3, or SEPA High + Medium) and the share in the lower one only (Flood Zone 2 alone, or SEPA Low). The shares are estimated by sampling points across the zone — up to 4,000 a zone (ours) — so they are a grid estimate, not a survey: the flood outlines are simplified to about 2 m before sampling, and the share is printed to the nearest per cent. A sliver of Flood Zone 3 too small to round to 1 % prints as "< 1 %" and still counts: no zone with a hit ever reads 0 %.

• Campsite in Flood Zone 3 (or SEPA High or Medium) — a warning: people sleeping in a mapped flood area need flood warning sign-up and an evacuation plan with a site map. Treating an event campsite as the NPPF's "more vulnerable" camping use is our reading of NPPF Annex F, which says nothing about temporary events. The NPPF is England's policy: outside England the warning says so, and that the Welsh (TAN15) and Scottish (NPF4) policies were not read — it rests on the mapped area alone.
• Campsite in the lower zone, or any arena, entry or car park in a flood area — a note with the shares and the source's own names.
• Never a fail. These are desk-study readings of national maps.

When flood was not checked

A reading that could not be made says so, by name — it is never shown as "no flood zone":

• "not checked: <nation> flood data not available" — the nation's service did not answer, could not be verified, or (Northern Ireland) has no source. Where a site straddles a border, only the part in that nation reads "not checked"; the rest is judged.
• "flood not checked for part of <zone>" — the zone now reaches outside the box that was fetched. Fetch again.
• "flood partly checked" — the outlines came back truncated at the server's 30,000-point budget, so the shares are a lower bound.
• "flood shares stale" — the zone moved since the fetch and the outlines could not be read again.
• "flood not checked" with the reason — offline, the fetch failed, not fetched yet, no boundary, no map location, site over 5 km, or the nation could not be resolved.

Not assessed

Ground: soil and drainage

The ground reading comes from one of two sources, and the block says which:

• England and Wales — LandIS Soilscapes (NATMAPsoilscapes, Cranfield University), read from our 100 m grid of the national map. It gives the soil's texture (loamy, clayey, sandy or peaty) and its drainage class (freely draining, impeded or slightly impeded drainage, naturally wet, surface wetness, or variable).
• Scotland — BGS parent material: the British Geological Survey's Soil Parent Material Model (1 km) and its peat layer, which give a texture but no drainage. England and Wales fall back to it too when a point has no LandIS soil class (water or unclassified) or if LandIS is ever switched off — the block then says why.

The caveats, which travel with every reading

• LandIS Soilscapes is a national 1:250,000 map that groups soils into landscape-scale units: it gives the dominant soil of the unit, not of your site. Our 100 m grid of it means a site near a unit boundary may sit in the neighbouring class. Where a point has no class (water or unclassified), the most common class in the 100 m cells around it is shown, with the distance to its nearest cell. The site point is placed on the British National Grid by the OS Helmert transform, accurate to about 4 m — small beside the 100 m grid.
• BGS parent material describes what the soil forms in, to roughly 2–3 m — not the topsoil — on a 1 km grid. It has no pH reading and no shrink-swell rating.
• Both are a desk-study starting point, never a substitute for a site investigation or trial pits. The block and the appendix repeat each source's own caveats word for word.

The waterlogging reading is ours

Neither source says "waterlogging"; reading their classes as a wet-weather risk is our interpretation, labelled so on every finding:

Where the reading is slow-draining (or variable), the ground note adds two controls: car parks on grass need trackway or a wet-weather alternative (HSE's event-safety Transport page lists hardcore, metal trackway or temporary surfaces for routes that deteriorate in bad weather — linking it to the soil reading is ours), and the emergency route needs a surface for 12.5 t along its whole length (the gov.uk open-air events fire guide). Where peat is mapped, a separate warning says bearing capacity is likely to be low for structures and vehicles — ours, so it warns at most. A texture the source is unsure of starts "Texture uncertain —".

Typical weather: a 30-year average, not a forecast

The month comes from the event date (4 · Event). With no date set, the block says “set the event date to see the typical weather for the month” and shows no figures — it never falls back to today’s month or to an annual average. Where the build, live and derig days run into a second month, the block names both and says which month’s figures it is showing; that choice is ours.

Where the figures come from

They come from the Met Office UK and regional series (areal values from HadUK-Grid 1 km) — the Met Office’s published UK and regional series, under the Open Government Licence. Those files are themselves HadUK-Grid 1 km observations averaged over a region, so this is the same observational data as the grid, read at a coarser place. The honest limitation is how local it is — a regional mean, not your field — and which variables it carries. It is not weaker data.

Our own reading of the files is labelled wherever it appears: the 1991–2020 monthly mean is computed by us from the yearly rows (a month missing more than two of its thirty years is shown as not available rather than averaged), the units are ours because the Met Office pages state the quantity and not the unit, and the rounding is ours.

Which series your site reads, and how it was chosen

The Met Office regions are the Met Office’s own, not the ONS regions a postcode returns, and no boundary file for them is published. So the app maps one to the other with a fixed table that is ours, and every output says which series was used and how it was picked:

• Wales, Scotland or Northern Ireland — that nation’s own series. Two Met Office regions (England NW and N Wales, England SW and S Wales) straddle the England–Wales border; the table never puts a Welsh site in one, and that is our choice, not the Met Office’s.
• England with no region (no postcode near enough) — the England series, and the line says so.
• An ONS region we do not map (a renamed region) — the England series, and the line names the unmapped region. A new name never silently picks the wrong region.
• Not in the UK — a site the nation boundary places in no UK nation, with no UK postcode near it either (Dublin, Calais, the Channel, the Isle of Man, the Channel Islands), gets no reading: the UK series is not its weather. If the postcode lookup does not answer, the reading is not made rather than guessed.
• A lookup did not answer — if the nation boundary could not be read, the UK series is used and the line says a lookup did not answer; if the region lookup fails for an English site, the England series, saying the same. Such a reading is retried within minutes.

The 5 km HadUK-Grid is not loaded in this build

The Met Office’s HadUK-Grid 5 km monthly 1991–2020 averages (v1.3.2.ceda) would give a 5 km cell over your site rather than a regional mean, and adds wind, 10 mm rain days and summer days. It is open data under the Open Government Licence (DOI 10.5285/a7947ae607fd4be8994b940eebca8872), but downloading it needs a registered CEDA account and an access token, and the licence requires the catalogue record’s own citation to be used. Neither the files nor that citation is in this build, so no reading uses the grid and the app says so instead of implying otherwise. We never invent a citation, and we never assemble one from the DOI.

Wind and structures

With tents, stage roofs or towers on the plan, the checks add a Wind and structures note. It lists what is drawn, the month’s mean wind where the source has one, and HSE’s own words — take account of foreseeable wind loading and of ground strength and slope; where the completed structure is susceptible to the weather, monitor and measure the local conditions; in adverse conditions know what to do with the equipment to protect its stability.

The tower exclusion zone

For each tower on the plan (front-of-house, delay and lighting towers) the checks draw a circle of 1.5 × the tower’s height and note what live it reaches: the crowd zones (arena, entry, bars & traders, campsite), welfare areas, safer areas, car parks and tented structures. Production and backstage areas are not tested, and a note that finds nothing names exactly what it tested. That multiplier is HSE’s, from “Outdoor equipment to support speaker clusters, lights etc” (updated 12 October 2024), and it is conditional: HSE says such a zone may be prudent where no adverse-weather arrangements are in place. Drawing it as a circle, testing it against the zones that are live, and taking the height from the object you placed are ours.

• It is always a note — never a warning, never a fail, and never a statement that the zone is required.
• It never says a tower is safe or unsafe, and it quotes no wind speed or action level of any kind.
• A tower whose height is not available reads “tower exclusion zone not checked: this object’s height is not available” rather than a circle of nothing.

When the weather was not checked

As with flood and ground, a reading that could not be made says so by name, and the same words appear in the block, the appendix and the cover row: set the event date; no map location; site boundary not drawn; not fetched yet; offline; the weather service did not answer; the site is outside the area the Met Office series covers; the site could not be placed in a UK nation; the weather service’s answer could not be read; or the weather dataset could not be read. None of them is ever shown as a zero.

Credits

Each source's credit is printed wherever its reading shows — in the block, in the appendix and on Sources and what is ours:

• LandIS Soilscapes: Soil data from the LandIS Portal (Cranfield University): NATMAPsoilscapes, 31 Mar 2026, Public Data 2026, Open Licence. Licence: https://cranfield-portal.maps.arcgis.com/sharing/rest/content/items/91f00fd749314faa8356f9e41b65ff8c/data LandIS and Cranfield University do not endorse this tool or its readings. We use only LandIS Public Data under its Open Licence, from an offline download made by us; the app never queries the LandIS platform, and if the licence were withdrawn the Soilscapes reading would stop and BGS parent material would carry the ground everywhere. The LandIS Portal is where the data comes from.
• BGS: Contains British Geological Survey materials © NERC 2026.
• Environment Agency: © Environment Agency copyright and/or database right 2025. All rights reserved.
• Natural Resources Wales: Contains Natural Resources Wales information © Natural Resources Wales and database right. All rights reserved. Some features of this information are based on digital spatial data licensed from the UK Centre for Ecology & Hydrology © UKCEH. Defra, Met Office and DARD Rivers Agency © Crown copyright. © Cranfield University. © James Hutton Institute. Contains OS data © Crown copyright and database right.
• SEPA: ©SEPA 2025; this SEPA product is licensed under the Open Government Licence version 3.0, with SEPA's Flood Map Version 3.0 data attribution statements (5 February 2025), which go with every Scottish reading.
• Met Office (the typical-weather figures; OGL v3): Contains public sector information licensed under the Open Government Licence v3.0 The series is the Met Office UK and regional series (areal values from HadUK-Grid 1 km); the 1991–2020 monthly mean of it, and the mapping from an ONS region to a Met Office series, are ours.
• HadUK-Grid: not in use in this build. It is OGL v3 with Permitted Use “Any” (DOI 10.5285/a7947ae607fd4be8994b940eebca8872), and its licence requires the catalogue record’s own citation, which we have not read — so no reading uses it and no citation is composed here.
• Nations: Source: Office for National Statistics licensed under the Open Government Licence v.3.0. Contains OS data © Crown copyright and database right 2026.