Question on water management around roads

DePurpereWolf

I'm not from around here, so maybe someone can clarify this for me.

I've driven around in many countries, what seems weird about the roads in Ireland is the lack of ditches in the shoulders. The smaller roads prefer the stone wall topped off with a high hedge. But even with the newer national roads it almost seems like the architects forgot it rains in this country. So you get these broad water streams across the 4 lane highway whenever one side dips more than the other, excellent for aqua-plaining.

I'm not talking about the sewer system. Ditches are used in the country when there is no sewer system around. You want to keep water off the road so it doesn't freeze over at night and create black-ice. With heavy rainfall like we're having now, it would prevent potholes from getting larger.

Even in the estate I live in, which is about 30 years old, there is no ditch around, and the grassy fields have been spongy since April last year (apart from the last couple of weeks, when they were frozen)

Is there any reason for the lack of ditches?

Amtmann

Motorways are flanked by numerous large attenuation ponds which capture water run-off from the highways. Before the water enters the ponds it is filtered by a petrol interceptor to remove contaminants. I'm not sure about other roads to be honest.

loyatemu

Furet wrote: »

Motorways are flanked by numerous large attentuation ponds which capture water run-off from the highways.

where this falls down is that on a lot of our motorways the water doesn't run off in the first place. it just sits on the road - the M11 (Bray) is particularly bad, you really notice it when you join it from the M50 (which seems to have better drainage).

parsi

Furet wrote: »

Motorways are flanked by numerous large attentuation ponds which capture water run-off from the highways. Before the water enters the ponds it is filtered by a petrol interceptor to remove contaminants. I'm not sure about other roads to be honest.

So that's what they are...

Amtmann

loyatemu wrote: »

where this falls down is that on a lot of our motorways the water doesn't run off in the first place. it just sits on the road - the M11 (Bray) is particularly bad, you really notice it when you join it from the M50 (which seems to have better drainage).

I'm not familiar with the M11, but on the M8 the water drains away very effectively into the ponds except at one location on the Watergrasshill bypass, but even there it's not a deplorable situation. I'm interested to hear how the M6 handles excessive rain.

101sean

I suspect that in a lot of cases road widening has removed the ditches and any drainage installed lost through lack of maintenance. In a lot of cases the only drainage is a hand cut grip in the verge or a hole in a wall. The worst potholes arise in the flatter poorer drained lengths.

A case in point is a stretch of the N24 between Limerick Junction and Tipp town, a 500m length has broken up completely and is downright dangerous. It got worse during the day as trucks ripped it apart, by 16.30 it was like a ploughed field and should have been closed. The cause is poor surface and sub surface drainage multiplying any frost damage immensely and badly affects many of Tipp's roads, over the border in Limerick it's nowhere as bad. Don't know how bad other counties are but your suspension will tell you when you've crossed into Tipp :rolleyes:

DePurpereWolf

Furet wrote: »

Motorways are flanked by numerous large attenuation ponds which capture water run-off from the highways. Before the water enters the ponds it is filtered by a petrol interceptor to remove contaminants. I'm not sure about other roads to be honest.

Motorways are more like examples of how it should be. But it's only a small percentages of the roads in Ireland. The national roads are not designed that well (to say the least)

An example from around where I live, the N24 near Killeens in Cork, going towards Blarney. It's a brand new stretch of road, surface is (still) perfect. But at heavy rain you have a stream 5 meter stream going from left to right.

Most national roads don't have any drainage, this might be because they are old, but even with new stretches it's not apparent.

Brian CivilEng

Just because you can't see the drainage doesn't mean it's not there. Most of the drainage on Irish roads is provided by French drains. These are trenches that are dug along the verge with a pipe placed at the bottom. The trench is then backfilled with stones of the same grade. The trench is then porous enough that surface water will filter down to the pipe quite quickly, but if a car leaves the road it wont fall into the trench due to the stones. Here is an explanation:
http://en.wikipedia.org/wiki/French_drain

The whole carriageway should have a gradient that falls towards the verge, normally 2.5%.

kagni

101sean wrote: »

A case in point is a stretch of the N24 between Limerick Junction and Tipp town, a 500m length has broken up completely and is downright dangerous. It got worse during the day as trucks ripped it apart, by 16.30 it was like a ploughed field and should have been closed. The cause is poor surface and sub surface drainage multiplying any frost damage immensely and badly affects many of Tipp's roads, over the border in Limerick it's nowhere as bad. Don't know how bad other counties are but your suspension will tell you when you've crossed into Tipp :rolleyes:

Seems to be the same across a lot of the N24 so I hear. It must be more than poor drainage, maybe the quality of the tarmac or the way it was laid could be part of the problem?

101sean

The is very little proper tarmac on these bad stretches, just successive layers of surface dressing over compacted stone base, you can see it in the deeper potholes! It's only in the last 2-3 years that Tipp have been resurfacing roads properly, before that they just put a layer of 804 down and couple of layers of tar and chip or a thin layer of proper tarmac at best and hoped it stood up to 40 tonners.

dowlingm

The ditches being removed sounds like a lot of the country roads in North Cork near where I grew up. It seemed to have happened sometime in the late 80s or early 90s but I don't recall exactly when. At least back then you could stand on the raised portion of the ditch to evade the lunatics doing 60mph (as it then was) on a barely double wide road with minimal markings and short sightlines.

jrar

The N7 along the section between junc. 4 and junc. 8 is very bad for sitting water when there is any bit of heavy rain - given that it's a new 3-lane HQDC, the amount of spray on wet days is deplorable, and visibility on what is a high-speed road is definitely impaired as a result.