Drainage issues with red orc from old coal mines

[thameslade]

We have a field drain 4" with a good bit of stone around it that clogs up in less than 2 years!
the whole lot stone and pipe is covered in red orc from old coal mines which seems to rise up during the winter and I was wondering if anyone on here may have a solution to my problem apart from making an open ditch which is about 100M away from one.
Thanks in advance

 

[Derrick Hughes]

X

 

[hally]

X

Local coal mine had to spend millions due to this problem, a good few sediment ponds.

 

[Andrew1983]

6inch pipe would help and an easy access point to shove a jetter up it.

 

[Sharpy]

Lime.

 

[Phil P]

What type of stone is round the drain? I’m sure I read the crushed limestone make the problem worse! Could be wrong though.