posted 8 years ago
It is kind of hard to tell from the picture, but the problem seems to lie in the fact that the drive is not built properly, and any short term remedial efforts are really not going to be adequate or long term. It really does not matter where anyone lives, if there is a slope to the road surface, water has to be accounted for. There is nothing wrong with shelving out a road on a steep slope, cutting the material from the uphill side to the downhill side is a very common and effective method of building a road along a slope. However, to last there has to be drainage, and that is where this road seems to fall short.
The original builders appeared to have chosen the more inexpensive route of outsloping the road; that is, even though they shelved the road from the high side to the low side, there is some slope (1-2%) to allow water to run off the surface of the road and down the hillside. This is a cheap way to build a road, but not a very good way. If the area does get snow, this can make winter travel treacherous in the winter, but probably not an issue for you in the United Kingdom. However, because the road winds its way up the hillside, as well as across it, means there is a lot of water coming down the road. In a perfect outsloped road, this water would get to the edge of the road quickly and do little damage. With vehicle compaction and less than ideal grading however, what most often happens, and probably what you are getting, is large volumes of water flowing down the vehicle ruts and to the inside of the roadway. This water is gathering momentum and volume the further it gets down the hillside until it finds a spot where it can cross the road and then wash out. A VERY common issue with outsloped roadways.
The best way to cure this is with a ditch on the uphill side of the road. This can be an issue if the area is solid rock, but it is the only real alternative. You can get this ditch in one of two ways, dig a ditch if it is not solid rock, or build your roadway up so there is a ditch. Then the roadway is sloped to the uphill side. Now as rain comes down, the water flows off the road and into the inside ditch, and with rock check dams, the water is slowed and thus does not erode. The water travels down the ditch every few hundred feet until a culvert is located across the road where water is allowed to escape. To prevent erosion at the outlet of the culvert, it is armored with rock.
As with any erosion control measures, it really is a matter of slowing down the flow of water. Reducing the volume by discharging the water as quickly as possible.
If the roadway does not get plowed for snow removal, you could try wipers, swales and channel culverts, placed diagonally in the roadway to divert water coming down the roadway without turning your outsloped roadway into an insloped roadway, but I am not sure how well they really work. It might be worth trying only because it would be so less expensive then the true insloped fix. A word of caution on the swales though. While they are great for fields and food plots, driving over a swale kind of sucks, especially if pulling a trailer or making a few runs up the roadway everyday. The rolling nature of them gets old pretty fast. I am putting in a road this summer up a sleep hill and it has to be soil engineered, but I am hoping above all hopes that she does not call out for swales in my roadway as they really suck to drive over.