Llangennith in 3D

Building the coast…

SwellWind

Forecast

Time

Where to go, best first

Try your own swell

Set by the forecast hour. Move them to see what another swell or tide would do. They set the main swell; the forecast's second swell, if it has one, stays as it is.

Coming fromPeriodHeight offshoreTideLowestMean sea level 0mHighest

Breaking height in the model

The model's own height where the waves break at each spot on it. It shows how the swell, period and tide change things, but its sizes aren't tuned like the forecast's, so they can differ.

View

Mark where waves break Only where they break over sand or at a spot's own reef, not on rocks, cliffs or harbour walls. Each bar stands 40 times as tall as the wave there.Show the wind on the water Smooth where it's only just left the land, ruffled and darker where it has roughened the sea, flecked white where it's blown out.Vertical scale

Keys, once you've clicked the model: arrows to pan, + and − to zoom, [ and ] to orbit, Page Up and Down to tilt, 0 to face north.

How it's made

Land and beach: Copernicus GLO-30, a 30 m global elevation model from satellite radar. It includes buildings and trees.

Seabed: EMODnet Bathymetry's DTM, about 115 m between soundings, moved from the lowest tide to mean sea level (4.7m apart here, from three months of tides). The strip between the shore and the survey is filled in smoothly, so the inner surf zone is approximate.

Waves: the forecast's swells, up to two, each traced as rays across that seabed. They turn towards shallow water, grow as they slow down and break when they reach 0.78 of the depth. Diffraction is approximated by letting their energy spread sideways along each crest, so a shoal's focus widens and some swell reaches into the lee of a headland. Where a weaker train of crests crosses a stronger one, it's drawn faintly. Where both swells break, their heights add by energy, as the forecast adds them. There's no wind or current.

Where you can surf: the beaches, rocks, cliffs and harbour walls on OpenStreetMap. Breaks are marked only over sand, or at a spot whose waves break over reef.

Wind on the water: the forecast wind builds chop over open water, so the sea is smooth where it has only just left the land, as offshore beside a beach or in the lee of a headland, and rougher the further it has blown. It uses the forecast's own limits for clean, choppy and blown out, and is held to the forecast's call where Llangennith's waves break.

Wave shape: lefts or rights, hollow or fat, from published surf guides for each spot, picked by the hour's tide, swell and size, and crumbly in an onshore wind. The model's seabed is too coarse to see the sandbars and reefs that decide it.

Lidar © Environment Agency copyright and/or database right, Open Government Licence v3.0. Copernicus DEM GLO-30 © DLR e.V. 2010–2014 and © Airbus Defence and Space GmbH 2014–2018, provided under COPERNICUS by the European Union and ESA. EMODnet Bathymetry Consortium, EMODnet Digital Bathymetry (DTM), CC BY 4.0. Beaches, rocks and cliffs © OpenStreetMap contributors, ODbL.