Marius you better put your pond building on hold and start building your ark!
8000ltr is an extreme amount of water to come down from the heavens. The surface area of your pond can't be much more than 8 square meters which in my mind means a m**r of an amount of water, something like a monsoon or tsunami. The farmers in the FS are probably complaining because they can't plough or plant etc.
What was the rainfall during the time it rained?
Is there not water spilling from the roof into your pond? I had that problem and needed to modify the roof runoff to miss the pond.