Highwater Field

Datum — listed here as Highwater Field — reports what the ground under you does: how far you are above the river or the sea, what the slope above you has done before, and what to watch for with your own eyes. It works with no signal, once you download the region you are going to. It will never send you a warning. It has no sensors and receives nothing. Silence from this app means nothing at all. Download before you travel, on wifi. In the valley it is too late. WHAT IT SHOWS • Your height above the river or the sea, and whether that height was surveyed or estimated — the app always says which. • A cross-section of the ground where you are standing, with the level past events reached, drawn solid where surveyed and dashed where estimated. • All six hazards for the region — flooding, landslides, avalanches, ground shaking, tsunami, lahars — including the ones with nothing recorded, shown as explicitly empty rather than left out. • What is in the record, and what is missing from it. • A route to higher ground where there is one, and a plain statement where there is not. WHAT TO WATCH FOR Eleven observable cues, sorted by how long you may have — a roar from upstream with no rain, the sea pulling back, new cracks in a slope. The app cannot notice any of them. You can. Printable as a single greyscale A5 sheet for a wall, which works when no phone is charged. WHAT IT IS NOT This app is not an emergency application. It is not connected to any warning system, it receives no alerts, and it cannot tell you that anything is about to happen. Nothing in it means you are safe. It is a record of terrain and of past events, for reading before you travel and while you are there. Data: Copernicus DEM, USGS 3DEP, SRTM, HydroSHEDS (WWF), OpenStreetMap contributors (ODbL), and regional hazard inventories credited per region. Coverage is a small number of seed regions and the app says plainly where it has none.