ᐅ Rainwater: Discharge into ditch, gravel, soakaway/seepage trench, cistern/rainwater tank – any experiences?

I want to divert rainwater from a few hundred square meters of roof area and have submitted an application to the local water authority for "discharge into a water body." Actually, I plan to interrupt this discharge in the medium term by installing a cistern to also use the rainwater in the garden. Now, the water authority is reviewing whether infiltration could be an alternative to discharge, which they would prefer due to the intermittent nature of the rainwater flow.

At the moment, I am still neutral on this, but I would like to hear your opinions before the next discussion with the water authority.

• There is enough space available
• The discharge would possibly take place into a small valley (slope) at the edge of the property
• The overflow of a soakaway trench or cistern would do the same
• Instead of a filled plastic tank (soakaway trench), I would prefer (and possibly propose) a soak pit filled with gravel
• We have heavy clay soil here, meaning that with any option the water will (possibly delayed) reach the small valley
• The neighbor uses the concept roof -> cistern -> overflow -> small valley, so it should be possible and approvable
• I could also imagine roof -> cistern -> gravel soak pit if that would be preferable to the water authority
• Regarding costs, I do not like the soakaway trench because I see little added value for the 1000€ spent on the tank (a cistern is just as expensive, but I see the added value there)