Road Drains - Design and Use

The bottom of Penymynydd Rd is near  the end of a considerable decline from Penymynydd. A stream that runs down Penymynydd Rd has been "piped". The contents join a stream in the fields after going under Chester Rd.

Also we have the road drains running down Penymynydd Rd

At the Chester Rd / Penymynydd Rd junction we have houses that were built "below" the road level.

So when we have considerable amounts of precipitation the drains cannot cope, drainage comes up through the grids over the road causing a road hazard and flooding gardens of those residences below the road level on Chester Rd.

To this is added lifting manholes from the piped section that cannot cope with the stream content.

There are two issues here.

The stream running down Penymynydd Rd was piped underground with an adequate diameter bore.
This was then modified to a smaller bore near its exit into the stream at a later stage. Who allowed permission for this I don't know. The Utilities are aware of this they have had the camera down the pipes. The engineer I spoke to thought it crazy. ( Its what we have planning for)
I am of the opinion that water backs up the pipe system forcing the lifting of manholes. with 1000's of gallons flowing onto the road.

The road drains running down Penymynydd Rd cannot cope with heavy downpours.
Too much development allowed up Penymynydd Rd without adequate drainage?

It has not been spelt out to me in so many words but I get the impression that I am considered the blame for this issue. You see its the traffic calming causing the flooding.

It makes the road 9 inches higher but it is still thought of as the cause. A law of physics some how being bypassed.

My thought is don't build houses at the bottom of large road inclines on land below the road.

At present our road drainage system is at capacity and flowing down the road.
The gardens need it.