Energy dissipation in steep paved ditch.

[ACtrafficengr]

We are rehabilitiating a low volume rural road (~300 vpd, sl=55 mph), and at one end, we have an asphalt paved ditch that is deteriorating. It's about 900 ft long on a 5-10% grade. Currently, vegetation growing in the thermal cracks provides some energy dissipation and filtration.

I'm looking for ideas for weirs, checkdams, etc. to manage the velocity and maybe improve water quality. It is in the road's clear zone, so I don't want anything that will cause an undue hazard to anyone that drifts into the ditch. Also, the right of way line is about 12 ft from the edge of shoulder.

Any suggestions?

 

[jgailla]

I don't know if this will work for your situation, but I have used CMU blocks set a couple of inches into concrete ditch pavement. It has worked well in the few situations I've used it, but I haven't used this method in areas likely to be impacted by traffic.

 

[civilman72]

Considering you are in the clear zone with a relatively high design speed, your options are limited.

Not sure what the budget is, but you could consider a set of storm sewer inlets to decrease the energy/erosion potential.

Maybe grouted riprap ditch with low profile (embedded) angular rock?

I also think you can use the CMU blocks mentioned above - which can include a design to allow vegetation to grow in the voids.

 

[beej67]

What's your budget? Location? Soils? My first thought is cut a one foot section out of the center of the ditch along its length and backfill with a couple feet of washed 57 stone, then cap it with pervious concrete or porous pavers. You'd maintain the conveyance capacity of the channel in big storms while promoting groundwater infiltration in smaller ones.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

angular riprap or gabions might work. not sure how any sort of concrete will help to manage velocity without energy dissipation. if you want to maintain concrete, then use drop structures to reduce the effective slope of the channel so the froude number is below 1, or better yet below .8

 

[beej67]

Pervious pavement would manage velocity by sucking the water up into the stone and infiltrating it. The only events with any velocity at all would be the ones that fill the entire infiltration trench.

But that's just one idea.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

there is no way that pervious pavement would be effective at 10% slope

 

[gbam]

Wow, 10% grade is toublesom. you may want to consult HEC14 and look at roughening for an increase in mannings, no even sure that would work. Have you considered collecting and conveying with storm drain pipes?

 

[beej67]

You could achieve the same basic premise with a slot drain into an infiltration bed.

There's really no other way to get any sort of 'water quality' element into this, as far as I can see, due to the grades.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[LincolnPE]

Need to get that channel grade down to ~2% with grouted riprap rundowns every ~200'.

 

[ACtrafficengr]

LincolnPE, the grade of the adjacent road is 5 - 10%, and I can't justify the costs of reducing the grade on a low volume rural road with a good safety record.

Has anyone tried the erosion control matting or reinforced vegetation on grades this steep? The sales reps will promise the stars, but I'm interested in real world results.

http://www.nagreen.com/erosion-control-products/vmax3-c350-permanent-turf-reinforcement.php

http://www.acfenvironmental.com/TurfReinforcementMats.html

 

[LincolnPE]

Crickets...

 

[dik]

Japanese Knotweed or something of that ilk... you either need to terrace it or build a series of walls or use angular BFR's... (big rocks) to dissipate the energy.

Dik