I literally mean the foundations for building the polytunnel and tank. Its amazing how much groundwork is required before you can start to put anything above ground. In the picture you can see the layers of ballast we are using as a more permiable floor for the polytunnel. The polytunnel is 40m x 8m so thats a lot of ballast but necessary as the topsoil is pure clay so any water just sits on it. This layer should allow the water to be absorbed and run out to the sides into drainage channels from where it can evaporate. The ballast has been harvested from an area of the site where we will now partly back-fill with spare topsoil but will also creat a wildlife pond. Its all recycling with us where possible! And also the concrete (hate the stuff but there are not sensible substitures for some jobs) base for the big rain-water tank. Its 6m diameter, so bigger than it looks in the picture.
The tank will have the capacity to store a months worth of spring rainfall and hopefully will supply around 60% of our water needs.
There is also a 5000 litre undeground sump tanks that will be used for recycling any spare water that will run-off after the plants have been watered.
I am learning a lot about irrigation systems.