Two houses on the same street can face very different hazards. Often the reason is hiding in plain sight: how high the ground sits and how steep it is. This guide explains why a few meters matters, and how we read it.

Elevation: water always goes downhill

Water obeys gravity. It collects in the lowest spots and drains off the higher ones. So the height of your ground above sea level is one of the simplest, strongest signals of flood and storm-surge risk.

CheckHazard reads elevation from a national terrain grid and sorts it into bands:

• Below 2 meters: this is roughly below typical storm-surge run-up. In coastal areas, this is a serious flag.
• Below 10 meters: still within the historical reach of big storm surges, and often low enough to collect rain flooding.
• Higher than that: flood and surge water is much less likely to reach you.

The gap between a lot at 1 meter and one at 12 meters, even right next to each other, can be the gap between regular flooding and a dry home. A small height difference is a big risk difference.

Slope: the other side of the coin

Slope is how steep the ground is, measured in degrees. It cuts both ways.

Gentle, flat ground sheds water slowly and calmly, but if it is also low, water can pool there. Steep ground drains fast, but steepness brings its own danger: landslides.

Here are the bands we use:

• Below 8 degrees: gentle. Low landslide concern.
• 8 to 18 degrees: rolling ground with moderate runoff.
• 18 to 30 degrees: steep, and landslide-prone in heavy rain.
• 30 degrees and above: an extreme gradient, the kind of slope where landslides initiate.

So a steep hillside lot might be safe from flooding but exposed to landslides, while a flat low lot is the reverse. Neither number alone tells the whole story, which is the point. You can read more on the elevation and slope layer brief.

Why they work together

Real risk comes from the combination. Low and flat near a river or coast means flooding. Steep and high above a valley means landslides and, lower down, debris flow. Reading elevation and slope together is how you tell which kind of trouble a property is exposed to.

This is why our report does not just flash a single flood color. It reads the terrain, the waterways, and the hazard zones together, then explains the picture in plain language so you understand why the rating landed where it did.

What to do with it

Use the elevation and slope readings to sanity-check the other findings. If a property is flagged for flooding and also sits below 2 meters, the readings agree and the concern is real. If it is on a steep slope and flagged for landslide, same thing. When the terrain and the hazard zones point the same direction, take it seriously and bring it to a site visit.

CheckHazard does not replace a professional geotechnical or engineering survey. Elevation and slope are screening signals from public terrain data, not a substitute for an on-site assessment.