downpipe into no drain

I bought a '60's built bungalow with a flat roof garage attached. the roof slopes to the rear and the down pipe goes through the concrete then into a black 'plastic' 100mm pipe.

I excavated it tonight as i thought the drain was blocked. common problem around here. i went down to 1300mm but nothing. at the far end of the front garden is an inspection chamber for the main drain and that is 1200mm deep. although the ground level is higher there

the black pipe goes to a depth of 600mm then nothing but clay soil.

I would have thought a drain would have existed here but no. the clay is soaking wet.

is this normal/typical of the era for a single garage?

jfg, good evening.

Unfortunately not an uncommon practice, builder cutting costs, [I never ever heard of that before.??]

Several options.

If all on the surface is OK??? leave alone.

Excavate and run a drain from the Garage to the main storm drain?

Cheap "fix" get a water butt run the garage roof drain into the Butt, about 300.mm down from the top of the Butt fit an outlet, to the outlet fit a long length of plastic pipe, run the pipe around a flower bed or similar and cut small holes or cuts into the plastic pipe allowing water to trickle out of the Butt and disperse ? A tap on the base of the Butt will give you water for the garden Via a watering can??

Ken.

No its not normal, but it does happen, builder puts pipe in ground and then gets paid and customer finds out later that the pipe goes nowhere.