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Working out where water will cross a road?

Working out where water will cross a road?

Working out where water will cross a road?

(OP)
There is a mopuntain road here that winds its way down the spur of a mountain.  It is a dual carriageway highway actually with a kerbed centre median

I have noticed that when it rains you find that there are some places where the stormwater will run (in a stream) from the left to the right of the road (or vise versa), obviously causing serious safety issues with cars often aquaplaning into the centre barrier.  The road has SW inlets on both sides of the road depending on which way the super slopes, but they do not seem to be in the right place, hence the water crossing the road

I know that this has to do with the super-elevation and the longitudinal gradient, but have often wondered how one would go about designing for this.  If you can design the path the SW will follow you can obviously put the SW inlets just upstream of where the water will cross the road.

I can only think of doing this manually by creating a contour diagram of the road surface and then obviously the water will run perpendicularly to the contours, but this seems like a bit of a novice way to do it.

Are there any texts on the subject that are available or even software that calculates this once the geometric design of the road has been done?

RE: Working out where water will cross a road?

"can only think of doing this manually by creating a contour diagram of the road surface and then obviously the water will run perpendicularly to the contours, but this seems like a bit of a novice way to do it"

Novice? - maybe - but that's the way I'd do it.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Working out where water will cross a road?

Watch for the chicken.  When the chicken crosses the road, let the water follow.lol

RE: Working out where water will cross a road?

Highway design programs like MX will actually show you contours and flow arrows to enable this to be assessed and the drainage placed accordingly. When was the road designed, since this capability has been around for some time?

Otherwise manual contouring based on level information would seem to be the way to go, after the fact.

RE: Working out where water will cross a road?

One can either use the proposed condition contours or look at the profile grade of the new roadway to identify the low point crossings.  Also, if one looks at the existing contours one can determine where the runoff will accumulate.

RE: Working out where water will cross a road?

Isn't the crown of the road suppose to prevent this water from crossing the highway?

RE: Working out where water will cross a road?

With sufficient velocity, water will run uphill, so it may not follow the contours exactly as you might think.  If a stream of water was entering the roadway at an angle and with high velocity, it would trace a parabola on a flat sloped surface.  Perpendicular to contour lines is for low velocity sheet flow only.  Water can also simply back up behind the crown until it becomes deeper.  Than you can bet your bottom dollar that it will find a way to cross it.

RE: Working out where water will cross a road?

chicopee
Typically a drainage guy will have the roadway designer super the road if they are designing for overtopping, at least I do.  Also the crown is typically only up a couple of tenths of a foot from the edge of pavement.  The crown can also act as a weir.  The designer(s) just need to be logical with their designs.  For instance you should never ever place a super turn-over in a sag vertical curve (I have seen this before on a freeway).  

RE: Working out where water will cross a road?

(OP)
the super is perpendicular to the cetreline, if the road is steep enough water will flow diagonally across the road (esp on a bend)

I have seen this mentioned in some texts, but never seen a good explanaition of how to actually work it out

RE: Working out where water will cross a road?

"Isn't the crown of the road suppose to prevent this water from crossing the highway?"

On a straight stretch, it has that effect if the centerline crown in any cross section is higher than the edgre of pavement.  However, this is not true at curves where the wole road is generally at a constant slope in any cross section except at the transition section where anything goes...

Just take a bunch of good elevation shots.  The contours do not lie guys...

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

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