Puddled clay lining is wet clay spread 10-15 cm thick over the bed and sides of a channel and compacted by trampling or pounding until dense and smooth, which cuts seepage to about 10-15%. It is free and lasts 5-15 years, it cracks if it dries out, and a 100 m run of the standard channel needs about 11.5-17 m³ of clay.
Part of Aqueducts and Channels
Clay lining is the use of well-worked clay as a waterproof skin on a channel. It is the cheapest lining and suits irrigation, where a little loss and the need for repair can be accepted.
Wet Clay Swells Shut, And Cracks When It Dries
Clay particles are tiny and flat, and when worked wet and packed tight they leave almost no gaps for water to travel through. That is the principle of puddling. The risk is the reverse: clay that dries out shrinks and cracks, and a cracked lining leaks. The aqueducts page says to keep it wet or cover it with a thin gravel layer in dry weather.
Use clay with enough clay in it. The cistern-building page (Cistern Building) gives a hand test: the soil should hold at least 30% clay, and a squeezed ball of it should hold its shape. Sandy or silty soil does not seal.
What You Need
- Clay subsoil, dug clear of topsoil, stones and roots
- Water, to bring it to a workable, plastic state
- A trimmed channel, dug to the section with 10-15 cm of extra depth for the lining
- A rammer or people to trample it
- A thin gravel layer or a way to keep the lining damp
Method: Wet, Spread, Compact, Cure
Step 1: Trim the channel to the section plus the lining thickness.
Step 2: Wet the clay and knead it, removing stones, until it is smooth and workable.
Step 3: Spread it 10-15 cm thick over the bed and sides, working up from the bottom.
Step 4: Compact it by trampling or pounding until dense and smooth. Smooth the surface in the direction of flow.
Step 5: Cure for a few days, kept damp, before running water.
Step 6: Protect it: keep it wet in dry weather or cover it with a thin layer of gravel.
Worked Example
The standard section on the aqueducts page, 0.30 m bottom with 1:1 sides, dug 0.30 m deep (0.20 m of water plus 0.10 m freeboard). The lined perimeter is the bed plus both sloping sides: 0.30 + 2 × 0.30 × √2 = 0.30 + 0.849 = 1.15 m.
Clay per 100 m = 1.15 m × 100 m × thickness: at 0.10 m, 11.5 m³; at 0.15 m, 17.2 m³, about 17 m³. At seepage of 10-15%, a 5 L/s intake delivers 5 × 0.85 = 4.25 to 5 × 0.90 = 4.5 L/s.
Common Mistakes
- Clay that is too sandy. It never seals.
- Letting it dry. It cracks.
- A thin or patchy layer. Leaks appear at the thin spots.
- Not compacting. Loose clay is porous.
- Using it for drinking water. The aqueducts page rates it for irrigation and clay-rich areas.
What’s Next
- Learn next: Lining Materials — the other options
- Combine with: Vegetation Control — roots and weeds crack clay