Road drainage

Sheldons Brain

This is the M1 today. Now this is wet day, but more in the line of a once very 2 or 3 years wetness rather than once every 200 years. I think it should be possible to build motorways with proper drainage, especially one of the busiest sections in the country, so that service in maintained during rain.

murphaph

I suspect the drainage is built adequately in most cases...but drains get blocked if you don't maintain them. This is more often the problem in Ireland IMO.

_Kaiser_

murphaph wrote: »

I suspect the drainage is built adequately in most cases...but drains get blocked if you don't maintain them. This is more often the problem in Ireland IMO.

I dunno.. the M3 gets very bad in places and it's that way since day 1. Luckily though it's a very quiet motorway so that offsets the problem.

More likely that corners were cut I'd say. Wasn't that part of the M1 all redone recently as well? Should be no excuses!

Carawaystick

_Kaiser_ wrote: »

I dunno.. the M3 gets very bad in places and it's that way since day 1. Luckily though it's a very quiet motorway so that offsets the problem.

More likely that corners were cut I'd say. Wasn't that part of the M1 all redone recently as well? Should be no excuses!

Yeah, it's only built about a year.

Sheldons Brain

Carawaystick wrote: »

Yeah, it's only built about a year.

Indeed it is.

But then what do we expect, in a country where you allow a hospital A&E get flooded, you fix it up and allow it be flooded again a year later?

sgarvan

From looking at the road this morning and Google Maps (pre update), there are no "drains" along the lay-by side of the road. There are trenches full of stones. This will obviously take away some of the water flow, but after a dry spell like we have had and then all the rain it is not going to soak away.

It is madness that this road was upgraded to 3 lanes each side within the last year and it had to be closed. The 2 lane part of the road didn't suffer from closures. Corner cutting is to blame massively. Charge high and build low.

Brian CivilEng

Those trenches at the side of the road are filter drains, the trench is lined with an impermeable film, and at the bottom of the trench there is a perforated pipe which collects all the rainwater and conveys it to the discharge point. Filter drains are used as they are lower maintenance and less likely to get clogged than gullies. They also drain the subgrade of the road which is important as it prevents structural damage.

Filter drains are used when the road is at grade or in a cutting, when the road is on a fill (higher than the surrounding land) you use something else, such as a surface drainage channel, over the edge drainage or kerbs and gullies. Obviously when the road is on a fill then subgrade drainage is less important.

The storm water is conveyed by pipes to a discharge point, where it first goes through an oil separator to remove any residue of petrol etc from the cars, that would cause a problem if discharged to a river. The discharge is normally attenuated, you've seen ponds at the side of the motorways I'm sure. These balancing ponds restrict the outflow from the discharge point to the same outflow as a green field site. This is to reduce the likelihood of flooding in adjacent lands caused by the motorway.

As to why the drainage failed in this instance I can only speculate. Usually the drainage designer will simulate a wide variety of storms to see how the network copes, short intense summer showers, week long winter rainfall etc. This is to supposed to show that the drainage network can handle most likely storms that it will be subjected to in its lifetime.

annfield1978

abitofacomedian wrote: »

Those trenches at the side of the road are filter drains, the trench is lined with an impermeable film, and at the bottom of the trench there is a perforated pipe which collects all the rainwater and conveys it to the discharge point. Filter drains are used as they are lower maintenance and less likely to get clogged than gullies. They also drain the subgrade of the road which is important as it prevents structural damage.

Filter drains are used when the road is at grade or in a cutting, when the road is on a fill (higher than the surrounding land) you use something else, such as a surface drainage channel, over the edge drainage or kerbs and gullies. Obviously when the road is on a fill then subgrade drainage is less important.

The storm water is conveyed by pipes to a discharge point, where it first goes through an oil separator to remove any residue of petrol etc from the cars, that would cause a problem if discharged to a river. The discharge is normally attenuated, you've seen ponds at the side of the motorways I'm sure. These balancing ponds restrict the outflow from the discharge point to the same outflow as a green field site. This is to reduce the likelihood of flooding in adjacent lands caused by the motorway.

As to why the drainage failed in this instance I can only speculate. Usually the drainage designer will simulate a wide variety of storms to see how the network copes, short intense summer showers, week long winter rainfall etc. This is to supposed to show that the drainage network can handle most likely storms that it will be subjected to in its lifetime.

From a design point of view the tests are

Longitudinal sealed carrier drains must be designed to accommodate a one-year storm in-bore without surcharge. The design must be checked against a five-year storm intensity to ensure that surcharge levels do not exceed the levels of chamber covers. Combined surface water and groundwater drains must also be designed to accommodate a one-year storm in-bore without surcharge. A design check must be carried out to establish that a five-year storm intensity will not cause chamber surcharge levels to rise above the formation level, or subformation level where a capping layer is present. In carrying out this check it should be assumed that pipes are sealed and that back flow from pipes into the filter media does not take place.

http://nrastandards.nra.ie/road-design-construction-standards/dmrb/volume4/hd-33-surface-and-sub-surface-drainage-systems-for-highways

http://www.dft.gov.uk/ha/standards/dmrb/vol4/section2/hd3306.pdf

Drainage Design standards are very poor in general and are due for a comprehensive overhaul, particularily with regards to SuDS/ attenuation

ardmacha

On the other hand, it is worse in Detroit!

Carawaystick

The road in Detroit was not built last year....

hardCopy

Junction 5 Northbound on the M50 was regularly flooded before widening, even after widening there is still a decent puddle during a wet spell.