Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?

Deflection berm (splitter wedge)

Passive

One of 3 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.

What your site needs

Sloping ground with room upslope for the mound and a clear run for the deflected flow down both sides. Against a real debris or mudflow hazard this is a life-safety structure: its height, angle and siting are an engineer’s job, not a judgement from the catalogue, and a badly placed one moves the hazard onto someone else.

A compacted earth mound set upslope of the house with its apex pointing uphill, so a surge of water, mud or debris is split and passes down either flank rather than striking the wall. It deflects rather than stops. Built in concrete or stone instead of earth, the same idea is called a deflection wall.

Cost

Medium

Upkeep

Occasional

Skill to build

Intermediate

Lifespan

Indefinite as a landform, provided the face is kept vegetated against erosion and anything it has caught is cleared out

Embodied carbon

Low

Space / material use

High

Output timing

None

Skill to repair

Basic

Inputs

none

Outputs

• Hazard protection

Compare the 3 ways to meet this need

Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.

• Deflection berm (splitter wedge) (This page)
  Can I use it? Works in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: Yes
  Choose it if you want a surge of water, mud or debris from uphill split before it reaches the wall.
• Elevated finished floor level
  Can I use it? Not in a flat · New build only
  What does it cost me? Upfront cost: Low · Skill to build: Specialist · Upkeep: None · Change to daily life: None · Works without the grid: Yes
  Choose it if you are building new where water can rise, and want rooms that stay dry whatever the level.
• Diversion swale / intercept ditch
  Can I use it? Not in a flat · No rebuilding needed
  What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: None · Works without the grid: Yes
  Choose it if you want the runoff from the slope above led around the house by a simple ditch.

Sources

• LaRiMiT landslide risk mitigation toolbox, "Deflection structures (berms)" (Norwegian Geotechnical Institute / Klima2050): berms that "deviate the flow path to another area of the debris fan" rather than stopping it

Limitations of this page

We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.