Rainwater: stream inlet, gravel, soakaway, cistern: experiences?

I want to drain the rainwater from a few hundred square meters of roof area and have submitted an application to the Lower Water Authority for "discharge into a water body." Actually, I planned in the medium term to interrupt this discharge with a cistern in order to use the rainwater in the garden as well. Now the LWA is checking whether infiltration is possible as an alternative to discharge; they would prefer that because of the intermittent rainwater inflow. I am currently indifferent but would like to hear your opinions before the next meeting with the LWA.

[*]There is enough space available [*]The discharge would possibly take place into a ditch at the edge of the property [*]The overflow of a soakaway or cistern as well [*]Instead of a filled plastic tank (soakaway), I would prefer (and possibly suggest) a soak pit filled with gravel [*]We have heavy clay soil here, meaning that in every variant the water (possibly delayed) reaches the ditch [*]The neighbor uses the concept roof -> cistern -> overflow -> ditch, so this should be possible and approvable [*]I can also imagine roof -> cistern -> gravel soak pit if the LWA would prefer that [*]Regarding costs, I don’t like the soakaway because I see little added value for the €1000 for the tank (it’s clear a cistern costs the same, but there I see the added value)