Figure on approx. 20% compaction when working with soils. It's a common number used for estimating purposes in the landscape industry.
It can vary depending on the composition of the soil and the weight of the mix, but it's a good starting point so you can account for it without being surprised the following year. You lost more than 20% from year 2 to 3 so, as others have mentioned, it seems like a combination of decomposition and erosion contributed as well.
It can vary depending on the composition of the soil and the weight of the mix, but it's a good starting point so you can account for it without being surprised the following year. You lost more than 20% from year 2 to 3 so, as others have mentioned, it seems like a combination of decomposition and erosion contributed as well.