Correct, but it highly depends on the soil characteristics. The measurement here is Volumetric Water Content (WVC).
Soil is made out of Soil, Air, and Water. The balance of which changes with precipitation and temperature. The soil fraction remains constant, usually between 50 and 60%. It is soil after all. The rest is either microscopic air pockets or water. The air pockets are just void spaces which water could occupy. When there are no air pockets left. It’s just soil and water which of course is called Mud.
A VWC of .4 means it’s 40% water, which means that there likely isn’t much air left. This indicates that the soil can’t take much more water, and will start to run off into streams.
The VWC in which that happens varies. Sand for example saturates as low as .2 while Clay can go to .5 or even slightly higher. It just depends on the soil present.
We’re gathering data to try to estimate/ establish the thresholds not only each location but also each depth. In the future we hope to have some sort of parameter that goes from 0-100, so there isn’t the VWC guesswork of saturation.