ai-browser-optimized · src:e314736bf0cade58 · Apr 05, 2024

Advanced water harvesting in permaculture: design once, water less

Intent: design a water system that catches, stores, and sinks moisture so plants thrive with fewer hoses. Benefit: clear methods, simple sizing math, overflow planning, and maintenance routines that hold up in real yards and small farms.

Context & common pitfalls

Great harvests start with slow water. Most systems fail from flashy earthworks without overflow paths, undersized first-flush, roof water piped straight to erosion, and greywater used where it shouldn’t. The fix is a stack: map flows → size elements → build from top to bottom → give every component a safe overflow → maintain.

Execution framework: capture → slow → spread → sink → store → reuse → overflow

1) Map and measure first

Catchment areas: measure roof planes, paved strips, and compacted paths. Sketch arrows for wind-driven rain and typical runoff routes.
Soils: do an infiltration test. Fill a shallow hole with water and time how long it drains twice. Note slow spots for basins, fast spots for storage.
Hazards: septic fields, steep unstable slopes, building foundations, and tree protection zones.

2) Roof capture to storage that won’t bite you later

Gutters & screens: keep leaf guards clean. If debris is heavy, double your cleanout access.
First-flush diverter: size roughly 0.5–2 liters per square meter of roof depending on pollution load; drain to a mulched basin, not the foundation.
Cisterns & barrels: elevate or place on firm pads. Include a screened inlet, sediment sump, opaque walls, and a drain at the low point for cleanouts.
Distribution: gravity feed to drip where elevation allows; otherwise a low-flow pump with a filter and pressure regulator.
Overflow: pipe to planted basins or a swale network. The overflow route must handle the biggest storm you design for.

3) Simple sizing math you’ll actually use

Yield from a roof: harvested water ≈ roof area × rainfall × runoff coefficient. Many pitched roofs use ~0.9 as a coefficient. Convert units consistently.
Tank right-sizing: choose storage that bridges your typical dry spell: use per day × dry days = buffer volume. Add headroom for storm bursts.
Swale volume: approximate as trench length × average width × average depth. Plan freeboard so banks don’t overtop.

4) Earthworks that slow, spread, and sink water

On-contour swales: shallow trenches with a downhill berm on contour. Plant the berm with deep-rooted perennials and groundcovers. Add rock spillways at safe intervals.
Keyline patterning: rip or subsoil along keyline geometry to nudge water from valleys toward ridges, reducing concentration. Follow with cover crops to hold gains.
Infiltration basins: bowl-shaped depressions under downspout overflows; size to catch the first flush and a chunk of peak flow. Mulch deep; avoid tree trunk contact.
Rock rundowns & armored overflows: where water must drop, step it with stone or timber and geotextile. Never leave raw soil in a fall path.
Terraces or mini-terraces: on moderate slopes, short retaining edges with level planting shelves tied into swales.

5) Subsurface and wicking solutions

Wicking beds: raised planters with a lined reservoir, gravel, fabric, and soil above. Fill from a standpipe; include an overflow just below the soil layer.
Subsurface trenches (infiltration galleries): perforated pipe in gravel wrapped in fabric to spread roof water under mulch, away from foundations.
Biochar bands: in arid sites, mix biochar along contour bands to improve moisture retention near roots.

6) Greywater done safely

Only certain sources: showers, bathroom sinks, and laundry using plant-safe soaps. Exclude kitchen sinks and toilets.
Distribution: branched drains or mulch basins at shrubs and trees. Keep subsurface, avoid spray, and respect setbacks from buildings and wells.
Soaps & salts: choose products low in sodium and boron. Rotate outlet basins to prevent salt buildup.
Overflow & maintenance: every greywater system needs a simple diverter back to sewer or septic during storms or maintenance.

7) Micro-harvesters for tough sites

Fog or dew nets: fine mesh placed in prevailing fog or wind can yield small but steady water for non-potable uses in certain climates.
Zai or pocket pits: small, mulched holes on gentle slopes concentrate runoff at plant roots, especially for trees and shrubs.
Tree mulch basins: wide donut basins capture dripline rain; refresh mulch frequently.

Layouts that work (top to bottom)

Ridge to swale to orchard: keyline-ripped ridge, swales planted to nitrogen fixers and fruit trees, overflow stepping to a meadow basin.
Roof to cistern to drip: screened gutter → first-flush → tank on pad → filter → pressure regulator → drip under mulch in beds.
Greywater to food forest: bathroom drains to branched lines feeding mulch basins under shrubs and trees; overflow to a rain garden.
Patio to planter: slight grade to a gravel strip and subsurface pipe that feeds a wicking planter with an overflow to lawn or bioswale.

Operations & maintenance that prevent heartbreak

Seasonal checklist: clean gutters and first-flush, inspect tank screens and overflows, test pumps, flush filters, and rake swale berms.
After big storms: walk the overflow paths. If water cut new channels, armor those paths and plant quick cover.
Drip audit: check emitters for clogs, look for wet/dry patterns, and flush lines at end caps.
Recordkeeping: log rainfall, tank levels, and observed infiltration. Adjust spacing, mulch depth, or emitter rates accordingly.

Troubleshooting: symptom → likely cause → fix

Tank overflows near the house: undersized or missing overflow line. Fix: upsize and pipe to a planted basin or swale.
Swale berm slumps: saturated soils or steep banks. Fix: flatten side slopes, add plants with fibrous roots, and include rock spillways.
Drip clogs: algae or sediment. Fix: opaque tanks, better filtration, periodic line flushing.
Greywater odor: pooling or anaerobic zones. Fix: distribute broader via branched drains, add mulch, and rest basins between uses.

Methods, assumptions, limits

Methods: roof capture with first-flush, cistern storage, on-contour swales, keyline ripping, infiltration basins, subsurface galleries, wicking beds, safe greywater routing, and armored overflows.
Assumptions: typical residential or smallholding scale, ability to place tanks safely, and access to basic earthmoving or hand labor.
Limits: contaminated roof runoff, high water tables, unstable slopes, or floodways may rule out certain features. Follow local codes for greywater and storage.

Tips & common mistakes

Design overflows first. If it can’t fail safely, it isn’t finished.
Mulch thick on basins and swales; keep bark off trunks.
Use level tools (A-frame, water level, laser) for true contour; guessing invites erosion.
Stage projects uphill to downhill so each piece hands water gently to the next.
Choose plant guilds that tolerate occasional saturation on the swale berm and drier crowns upslope.

FAQ

Can I drink harvested rainwater?

Not without treatment and local approval. For irrigation and flushing, screening and first-flush usually suffice. Potable use requires proper materials, disinfection, and compliance with health codes.

How much storage do I need?

Enough to bridge your typical dry spell while leaving room for storm surges. Use the simple sums above, then add overflow to earthworks.

What if my yard is tiny?

Prioritize roof-to-barrel-to-drip, one or two small basins, and a wicking bed. Even micro-systems cut irrigation a lot when mulched well.

Safety

Structural: full tanks are heavy. Build pads level on compacted base; anchor tanks in windy areas.
Health: screen inlets and overflows against mosquitoes; keep non-potable water labeled; follow local rules for greywater placement and setbacks.
Earthworks: call utility locators before digging; avoid cutting into unstable slopes; armor spillways to prevent gully formation.

Sources

Further reading: The Rike: advanced water harvesting techniques in permaculture systems