Debris Flow & Alluvial Fans

A debris flow is a fast-moving slurry of mud, rock, and uprooted trees that races down a channel during extreme rain. Over time, that material spreads out into a fan-shaped deposit at the bottom of a slope, an alluvial fan. Both are mapped zones, and this layer checks whether your lot sits inside one.

This is a binary exposure layer: you are either inside a mapped debris-flow or alluvial-fan zone, or you are not. There is no Low / Medium / High here, because the meaningful fact is simply that the parcel sits in a path debris has taken before.

After major typhoons, debris flows have buried homes that looked perfectly safe on a normal day, because the danger only appears when an upslope channel unloads. The lot itself can be flat and pleasant.

Being inside one of these zones does not automatically make a property unbuildable, but it changes the foundation and siting conversation completely. It is exactly the kind of fact a glossy listing will never mention.

We test your point against the debris-flow and alluvial-fan exposure polygons mapped by MGB-DENR through the NOAH program.

If your point falls inside one, the report flags the exposure plainly so it can be raised with an engineer; if not, the layer stays quiet.

These zones are mapped by the Mines and Geosciences Bureau (MGB-DENR) and distributed through the UP NOAH program.

Because the layer is exposure-only, it reads as a clear yes/no in the report rather than a graded severity.