erosion on downstream edge of road 4

[queque]

A road crossing a Desert wash (Apache Junction,Az) is eroding on the downstream edge of the road. The road has a 4 inch layer of asphalt on it. It has scoured 2 ft. below grade on the downstream side and has eroded
about 2 ft. into and underneath road. Is there a formal engineering solution to this problem? I cannot locate typical discussions on USACE procedures or USFS techniques.
I appreciate any comments.
queque

 

[Ron]

A culvert or a spillway.

 

[cvg]

not surprising, this happens all over this region.
Either a) install culvert or b) construct a cutoff wall per MAG Detail 552.

A scour analysis should be done either way.

 

[msquared48]

You could use something to slow down the flow velocity like rock check dams... or some form other of energy dissipator.

If you smooth out the channel, it will only flow faster, possibly creating more problems downstream.

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

 

[queque]

cvg do you maen MAG details Maricopa Association of Governments Pboenix,Az?

 

[cvg]

yes MAG or you can also use ADOT C-19.10

 

[cvg]

see details attached

 

[queque]

cvg how about the MAG standards for a wash left bank, using pre-teated 5 ft. long 4x4 timbers as rip rap?
I am having trouble accessing ADOT MAG Standards.

 

[cvg]

MAG is available online. Not sure about ADOT but you can get a copy of the standards at the main Phoenix office downtown. have not used a timber revetment, but it might work

 

[JedClampett]

Dude, your wish is my command.

 

[queque]

Thank you JedClampett.

 

[oldestguy]

Take a look at "CE News", May 2011 edition as on line, or the printed copy, page 50. It has an article under the heading of "Products", 'Engineering Solutions' dealing with erosion prevention with some fancy products. Might be of some help. These magazines are free from Zweig-White LLC.

 

[queque]

Thank you. Great reference

 

[fattdad]

. . . arriving late to the party. I have nothing contrary to say about anybody's feedback. I just want to pose another item.

If you have erosion along the side of a pipe, that's undermining the road, there may be a "piping" problem that's occurring along the soil-to-pipe interface. When the floodwaters back up in their efforts to go into the inlet, there will be some hydraulic gradient acting on this interface. If the soils along the interface are not in intimate contact with the pipe, piping can occur from the outfall and upwards towawrd the inlet.

The "best" way to address this is to envelope the lower 1/3 of the pipe in gravel. That way, when the seepage forces exit into the gravel, the gravel is under confinement and piping can't progress.

In the absence of a photo, it's hard to know which of the approachs is best for your project. I have just seen three or four pipe failure from this mode.

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

this is in the Sonoran Desert, near Phoenix. 7 inches of rain in a good year. I would not expect a culvert at this dry wash "dip crossing", very few in Apache Junction have culverts. They may flow once or twice a year for a few hours during the summer monsoon and rarely if ever during winter storms. Piping is generally not a concern as the gradient is not high enough and duration of flow is very short, besides they usually don't have culverts. However, this infrequent flow may be enough to cause scour, depending on the tailwater conditions. Dropoff on the downstream side of the crossing could be a foot or two if the road was built on some fill. The typical solution is just to provide scour protection. The standard details for MAG and ADOT address this with a cutoff wall. Riprap is probably also necessary.

 

[queque]

cvj are you with ADOT? pH No?

Thx , queque

 

[cvg]

no - consulting firm occasionally doing work for ADOT

 

[dgillette]

CVG - Seven inches of rain may be the average down there, but it's probably a bimodal distribution, dust or deluge. Last time I was down there (last Feb or March), I spent 48 hours cooling my heels, waiting for the dry wash to get dry enough that we could get to the site in a 4x4 truck. Thought about wading and hiking, but the water was fast enough to be scary, and nobody else in our group was that ambitious.

DRG

 

[cvg]

DRG - you are correct, although most dry washes don't run during the winter months, mainly during the more intense summer monsoon storms. It does depend greatly on your geographic location, if you get into the higher elevations, you will see a lot more precipitation.

 

[queque]

cvg -My first rainfall runoff study included installing a rain gage at the Hwy 60 just east of Apache Junction.Circa 1966. It rained 0.5 inches in 5 minutes. It was so intense that it washed out a trailer court and trailers as the flood crossed HWY 60 heading southward from the area. Actual Dranage area was 0.5 sq. mi. We (USGS) published a Source area Concept OF RAINFALL RUNOFF (RESEARCH PAPER).