FEMA Levee Certification 1

[Arizona3106]

I will be involved in the FEMA certification of an existing levee. The levee is up to 20 feet tall, 2:1 slopes with 12-inch thick, rock filled gabion mattress protection. The levee is 15 years old with 6 to 7 feet of freeboard, and no signs of any stability issues.

I am looking for any information on the best way to proceed in regards to the following. What methods should be used to determine seepage through the foundation and foundation stability?

1. Engineering analyses that evaluate levee embankment stability must be submitted. The analyses provided shall evaluate expected seepage during loading conditions associated with the base flood and shall demonstrate that seepage into or through the levee foundation and embankment will not jeopardize embankment or foundation stability.

2. Engineering analyses must be submitted that assess the potential and magnitude of future losses of freeboard as a result of levee settlement and demonstrate that freeboard will be maintained within the minimum standards. Detailed settlement analysis using EM 1110-1-1904.

 

[cvg]

USACE has some good documents online that may help. You could start with:

EM 1110-2-1913, 30 April 2000, Design and Construction of Levees

Don't forget to look in the references, Appendix A

 

[BigH]

Try:

http://www.ussdams.org/materials.PDF

http://www.derm.qld.gov.au/water/regulation/pdf/guidelines/dam_safety/appendix_04.pdf

http://www.derm.qld.gov.au/water/regulation/pdf/guidelines/dam_safety/appendix_05.pdf

 

[GeoPaveTraffic]

Arizona3106,

Have you ever designed a levee?

 

[Arizona3106]

@GeoPaveTraffic - No, I have not.

 

[GeoPaveTraffic]

If you have not worked designing levees, why do you feel you are qualified to perform certifications for FEMA?

That said, you will need to perform underseepage and through seepage calculations. As cvg pointed out EM 1110-2-1913 is the standard, you will also need ETL 1110-2-569. Note that these documents assume that the flood duration is long enough to create a steady seepage condition at the full flood stage.

Settlement is gernally not a problem with older levees unless there is a history of long term settlement or extensive fill needs to be placed to raise the levee.

Don't forget that the 100-year flood level has to be determined and that you will be certifying that as well.

Also, make sure to state how long the certification is good for and what ongoing maintainence is required to keep the certification current.

Lastly, I suggest that you talk with your insurance company agout what kind of coverage you will have for the project once you sign the FEMA certification form. Most insurance companies will decline coverage for certifications.

 

[cvg]

settlement can indeed be a serious problem if there is subsidence and that is a very likely possibility in some areas of Arizona. Fissures are also known to exist and possibly running under levees. (I assume the levee is in Arizona...)

Regarding insurance for certifying levees, I have found very few engineering firms willing to certify a levee. They are being stopped by their legal counsel, not just the insurance company.

By the way, personal experience designing a levee is not a pre-requisite to certification, however it certainly would help. Experts to help with H&H, geology, geotechnical, structural as it relates to levee or dam embankment design are necessary if you want to reduce your risk. Asking for general pointers on this website does not give me a warm and fuzzy feeling.