· Michael Blair
Infiltration solutions put water into the ground rather than moving it elsewhere. That requires ground willing to accept it, and Middle Tennessee clay accepts it slowly.
Test before designing
Dig a hole, fill it with water and time how long it takes to drain. If it is still holding water the next day, infiltration is not a workable strategy at that location.
It takes a day and it prevents an expensive mistake.
Sizing for clay
A dry well must hold the design volume long enough for the soil to accept it, which in clay means considerably larger than the same well in sand.
Undersized wells overflow in the storms they were built for, which is when they are most needed.
- Percolation test before designing anything
- Size for clay rates, not generic figures
- Place well away from the foundation
- Rain gardens need the right plants and a real depth
- An overflow route for storms that exceed the design
Rain gardens
A shallow planted depression that holds runoff and lets it soak in. They work in Middle Tennessee with amended soil and species that tolerate both saturation and drought.
The plant list matters — the middle of a rain garden and its edges are very different conditions.
Always plan the overflow
Any infiltration system will be exceeded by a large enough storm. Where the water goes then should be a design decision rather than a discovery.
An overflow directed somewhere harmless is the difference between a system that fails safely and one that floods a basement.