Stormwater Pond Embankment Design

[szymancp]

Hello everyone ---

I am looking for design references for stormwater pond embankment design... primarily, a document to design to for embankments less than 10 feet in height. Most likely, some of the water will be detained for a period of 48 hours or less.

I can find all sorts of documents for large earthen dams, concrete dams, large structures that have permanent retention fo water. But, not much out there for small structures, holding water for short periods. I am workig on a steep site where we are fitting in some detention ponds... and I would like to get a good design document in hand that I can trust.

Thanks!!!

 

[RWF7437]

"I can find all sorts of documents for large earthen dams, concrete dams, large structures that have permanent retention fo water."

The same principles apply whether the water is present for long or short periods of time. For some structures, rapid drawdown may be a problem but this is usually handled by using a very large factor of safety ( A.K.A. Factor of ignorance) .

good luck

 

[GeoPaveTraffic]

You might want to consider designing the same standards used for levee design.

However the short answer is that for structures around a maximum of 10 feet high with relatively short crest lengths; just design conservatively and let it be. The additional construction cost for a conservative design for this kind of structure is small. Check slope stability for a fully saturated long term seepage condition (even though it is unlikly to occure) and for a sudden drawdown condition.

 

[szymancp]

Thanks for the info ---

I had considered designing to the standards for larger structures, but wondered if there was a safe alternative for design of smaller structures that would be less costly during construction...

But, you are right --- the construction costs for a small structure won't be all that much more for a bit more complexity.

Thanks again!

 

[jeffcivil2]

The best guideline for a non-degreed engineer would be the Erosion Control design specifications which come from the state. If you are an engineer and plan on doing a hydrological analysis then you should go to the county/city's website of yours or the nearest large city and download their stormwater specifications or manual. There will be plenty of pictures in both of those, but I warn you these stormwater manuals can be 4" thick and full of nonsense.

 

[TerryScan]

Our state stormwater code is based upon NRCS Pond Code 378:

ftp://ftp-fc.sc.egov.usda.gov/NHQ/practice-standards/standards/378.pdf

If you check the NRCS guide for your state, it may have a customized version.

 

[cvg]

be careful as "small embankments" over 6' high which impound 50 acre-feet of water or more are regulated by the states and must be designed just like the "big dams". Look at the "Design of Small Dams" published by the USBR

 

[szymancp]

Thanks a lot for the links --- I actually remember that an old employer had the USBR Design of Small Dams book... I'm in the process of downloading the 1987 version right now.

Also printing the NRCS Pond Code 378.

To this point, I have been reviewing the USDA "Ponds - Planning, Design, and Construction" and the ACOE "General Design and Construction Considerations for Earth and Rock Fill Dams"

I really found the NYSDEC Stormwater Management Design Manual lacking in embankment design for ponds --- The current site I am working on is very steep and close to a critical roadway, so I am really trying to cover all bases and have a solid design from the start.

Thanks a lot!

 

[cvg]

NRCS (SCS) also has a lot of good information on dam design design and much of it online

 

[bob3306]

A small pond with a short detention period really isn't any different then an undersized culvert crossing a road. I think Dam Design might be a bigger hammer then you need for this one.

Its hard to go wrong with 4:1 max side slopes, easy to plant, easy to mow, no slope stability issues, and easy to drag yourself out of in that 100-year storm. Include a 10' wide flat spot on the top of the embankment, and some sort of stabilized auxiliary spillway.

I would try not to retain water much more then 3 feet deep, so its hard to drown in. If you have a lot of fall on the site, a series of not as deep ponds staggered might even fit better.

Also, rather then delving into the dam design references, you should ask the projects Geotech for recommendations. They have probably done this 1000 times in your area.

Good Luck

 

[EngineerofSteel]

szymancp: I am currently in the same search: a standard for earthen dams.

I found the army corps of engineers has standards for levees and for earth dams. In the manual for levees, they advise that levee design is for short term events.

For long term water holding, their manual advises earth dams or rock dams.

EM 1110-2-2300 for earth and rock dams
EM 1110-2-1913 for levees

The levee manual has a long list of design considerations and failure mechanisms. I believe it will be of use to you.