System Designs

The three patterns differ in scale and hydraulic loading rate (HLR) — the volume of water passing through each square metre of bed surface per day. Lower HLR means longer contact time and better treatment per pass; higher HLR means more throughput at the cost of removal efficiency. Use the design table for each pattern as a planning starting point, then adjust to your site.

Design A — Household runoff patch

Smallest scale. A learning project for one home, garden, or compound.

Design parameters (planning starting points)

Footprint	~0.3 m × 1–2 m, ~30 cm deep
Hydraulic loading	0.05–0.2 m³/m²/day (low; learning-scale)
Residence time (chip layer)	≥10 min at design flow
Slope	≤1 %
Substrate refresh	every 3–4 months

Materials

• Shovel.
• ~1 wheelbarrow of washed gravel (5–20 mm grain).
• ~1 wheelbarrow of washed coarse sand (~0.5–2 mm grain).
• 2–3 buckets of fresh hardwood chips (no aromatic softwoods).
• ~250 g of mushroom spawn (oyster or wine cap), or a chunk of colonized wood from an identified saprotrophic species.
• Straw or dry leaves to cover.

Build steps

1. Pick the low point where runoff already pools or moves through.
2. Dig a small trench about 30 cm wide, 30 cm deep, and 1–2 m long.
3. Layer it: 5 cm gravel, 5 cm sand, 15 cm wood chips mixed with spawn, then a straw blanket.
4. Direct inflow with a stone or pipe so the water enters at one end and leaves at the other.
5. Plant a couple of grasses or reeds at the outflow to root the soil.

Maintenance

• Inspect after every heavy rain, and at least once a week, for bypass channels around the bed.
• Top up straw cover after wind or storms.
• Replace wood chip layer every 3–4 months.

Failure signs

• Water flows around, not through, the bed.
• Standing puddles, anaerobic (rotten egg) smell.
• Visible erosion or collapse of the trench wall.

Design B — Community drainage mycobed

A shared channel that pre-treats runoff for a street, market, or small settlement.

Design parameters (planning starting points)

Channel geometry	60–100 cm wide, 30 cm deep, 5–20 m long
Hydraulic loading	0.1–0.5 m³/m²/day (community-scale)
Peak storm bypass	plan for storm flows above design HLR — direct excess to a vegetated swale rather than overwhelming the bed
Residence time (chip layer)	≥15 min at design flow
Substrate refresh	partial turn at 2–3 months; full rebuild seasonally

Materials

• Shovels and a wheelbarrow.
• Several cubic metres of washed gravel and coarse sand.
• A truckload-equivalent of fresh hardwood chips (oak, maple, willow, poplar, eucalyptus, etc. — no cedar, pine, juniper).
• Bulk mushroom spawn (or many pieces of colonized log) for wine cap or oyster.
• Straw bales for mulch cover.
• Rocks, logs, or gabions (wire cages filled with stones) to stabilize the channel walls.

Build steps

1. Map the natural drainage path after a rain. Mark where water already wants to go.
2. Carve a wide, shallow channel (60–100 cm wide, 30 cm deep). Keep slope gentle so water lingers.
3. Stabilize the walls with rocks or logs to prevent erosion.
4. Build the layered bed across the full length: gravel, sand, wood chips with spawn, straw mulch.
5. Add small check-dams of stone every few meters to slow flow.
6. Plant reeds or hardy grasses at the downstream end to start a plant buffer.

Maintenance ownership

Community designs only work if a specific group owns them. Before building:

• Name a maintenance lead and a backup.
• Agree on who inspects after heavy rains and who refills materials seasonally.
• Post simple signs in local language: "Pre-treatment bed — do not drink".

Failure signs

• Water cuts a new channel beside or under the bed.
• Persistent standing water and bad smell at the inflow end.
• Compacted, dark wood chip layer that no longer drains.

Design C — Mycelium + wetland buffer

A two-stage system: a fungal bed feeding a constructed wetland of reeds, sedges, and grasses.

Design parameters (planning starting points)

Mycobed stage	see Design B parameters
Wetland basin area	~1–3 m² of planted basin per m³ of daily flow (rule-of-thumb for vegetated polishing)
Basin depth	20–40 cm; saturated, not flooded
Hydraulic residence time (basin)	≥1 day at design flow for nutrient polishing and additional pathogen die-off
Plant density at maturity	4–8 stems per m² for reeds/sedges

Materials

• Everything needed for Design B's mycobed.
• An additional shallow pond or basin lined with clay, packed lime-stabilized soil, or geotextile (a strong landscape fabric used for soil separation).
• Reeds, cattails, sedges, or other locally appropriate water-tolerant plants — choose native, locally established species; avoid invasives.
• Stones or logs for outflow control.

Build steps

1. Build the mycobed as in Design B.
2. Excavate a shallow basin downstream, about 30 cm deep, with a flat bottom and gently sloped sides.
3. Line the basin with clay, packed lime-stabilized soil, or a geotextile fabric to limit infiltration into surrounding soil.
4. Plant reeds and sedges in the basin floor; they will spread to fill it.
5. Set the outflow at the far end so water passes through the full root zone before leaving.
6. Add a clear sign indicating the system is for ecological treatment, not drinking.

Maintenance

• Cut back reeds at the end of each growing season; compost cuttings safely.
• Watch for invasive species and remove them early.
• Refresh the upstream mycobed as in Design A/B.
• Test inflow and outflow water seasonally if possible — see Testing Water.

Failure signs

• Wetland dries out completely or floods constantly.
• Reed dieback over a wide area.
• Algal blooms or strong odors at the basin.