Diversion swale / intercept ditch

Passive

A shallow channel cut across the slope above the house, catching runoff coming downhill and steering it around both flanks to a safe outfall instead of letting it reach the walls. Ridging the excavated soil along the downhill side makes it a berm-and-swale; carried round the uphill face it is a horseshoe swale. Unlike a contour swale, which holds water to soak in, this one is deliberately inclined so the water keeps moving.

One of 3 ways to meet Flood mitigation. Build 1/3, Upkeep 3/3, Efficiency not rated. Cost, carbon and footprint below are rated against those 3, not in absolute terms.

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

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

Inputs

• Rainwater

Outputs

• Rainwater

Ranking in its sub-function out of 3 alternatives

Every option in this sub-function, with the value on each axis and a note on what drives it (this solution highlighted):

Build skill and upkeep burden are proxies (lower burden = simpler to maintain); the efficiency column is this sub-function’s ranking, 1 = best. “N/A” where an axis isn’t rated here.

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

Tutorials

No build tutorial recorded yet.

What this page does not tell you

No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.