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?

Diversion swale / intercept ditch

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

Ground sloping towards the building, room upslope for the channel, and somewhere downslope the diverted water can legally and safely go: this moves water rather than absorbing it, so it must not be pushed onto a neighbour

A shallow ditch dug across the slope above the house, gently tilted so it carries water sideways. Rain running down the hill is caught and led around the house to a safe spot. The walls and foundations stay out of the water’s path.

Cost

Low

Upkeep

Seasonal

Skill to build

Basic

Lifespan

Indefinite as a landform; the channel needs silt and debris cleared out and its banks kept vegetated, or it stops working in the storm it was dug for

Embodied carbon

Low

Space / material use

Medium

Output timing

Continuous process

Skill to repair

Basic

Inputs

• Rainwater

Outputs

• Rainwater

Compare the 3 ways to meet this need

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

• Diversion swale / intercept ditch (This page)
  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.
• 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.
• Deflection berm (splitter wedge)
  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.

Sources

• Building America Solution Center, "Swales, Drains, and Site Grading for Stormwater Control" (Pacific Northwest National Laboratory / US DOE; aligned to the IRC)
• Land for Wildlife South East Queensland, "Swales" - distinguishes a diversion swale (inclined, so the water moves towards the lower end) from a contour swale that holds water for infiltration

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.