The Brew Cabin

I am going to build an outdoor riding arena 45m x 25m. The arena will comprise 150mm of 40mm drainage stone and then 100mm of sand and rubber for the riding surface. I intend to put a drain around the the perimiter comprising 100m perfotated pipe at a depth of 1m and more drainage stone. Do I need a herringbone system as well across the surface of the school? If I make a mistake it will cost £,000s to fix but the additional drain will also cost a bit. This is a diy project to keep costs down. I am not an expert so can any replies be free of jargon.

I'd put cross-links in as well, Ian, with a maximum 10m spacing between them (or 9m for convenience). So, you;d have your perimeter, plus cross links at 9,18,27,and 36m along the long axis. This will involve and extra 100m of drainage, but it's not terribly expensive, and, as you say, it would be more expensive to try to correct it retrospectively.

If you're on heavy clay that's very slow to drain, you might want to reduce the separation between the cross-links to, say, one every 5 metres, or, even consider the use of a drainage composite layer beneath the sub-base.