3x3 and 8 meters deep does not sound practical to me.It would have to have vertical walls(sides) and that is nearly impossible.
If you do not have enough room for a pond a well would be nice,drill it on the higher part of the land so you can use the natural slope to flood irrigate.
We have two fish tanks that hold around 200 fish and we have no filter system.We let the water run out a few times per week and the water runs over the garden,free fertilizer.
One rai is just not enough imo,there will be a house,a drive way ,a shop and big trees for shade.
Permaculture is a good way of growing things,it keeps the labour down.