Lined Irrigation Pond Slope Question 3

[atook]

I work for a municipality and have some questions regarding an irrigation storage pond design. Specifically a PVC liner that does not have any cover on it, with slopes 3:1 or steeper. I’m aware that PVC should be covered with 12 inches of clean fill to protect it from UV.

Unfortunately the pond was designed with steep slopes to maximize volume. The engineer did not specify any cover for the liner. More so than UV resistance, the problem is liability, in that people or animals who enter the pond, cannot get out. We’ve already lost four foxes to drowning. We have an electric fence around the pond temporarily, but would like to keep from installing a chain link security fence around the pond because it is located on a golf course.

Are there any standards as to slopes for ponds in public places? At my old place of employment we started with a 4:1 slope to a depth of 3.5’ and changed slope after that. The thinking was that people/animals could walk out of a 4:1 slope.

I’m looking for industry standard or I’ve checked the IBC and can’t find anything. The stormwater guidelines I’ve seen are for unlined ponds. Any other places to look?

 

[cvg]

many agencies around here use 4:1 minimum and for retention basins 3 feet maximum water depth is typical unless fencing is to be used. Some of the concrete lined irrigation canals in this region are much steeper but have steps constructed at intervals to allow people a way out. Animals still have to swim and find their own way out typically.

 

[RWF7437]

Other places to look:

First, don't look for an "industry standard". Even if such a standard exists it probably won't protect you or your employer from liability.

Look at other golf courses in your area.
Look at public water attractions.
If the golf course is owned by the City, consult with your insurer and consider all options, including replacing the lining with something safer and more durable.

Sounds like a thoughtless design you got stuck with but public safety is a lot less costly than lawsuits, lawyers and death. Would simply covering the lining of the pond with large rock be all that expensive ?

good luck

 

[atook]

Thanks for the replies.

RWF7437: I should clarify that I'm not looking for an industry standard or code to say that the design is OK, I'm looking for it so I can go to the engineer and say, "This doesn't meet XX, and needs to be fixed"

 

[RWF7437]

Don't go to the "Contractor" and don't go alone.
Go to the Owner of the land, and his Engineer of Record and their Insurers and their Attorneys, but only after you ....

Go to your Attorney and Insurance Rep. and discuss with them the laws and insurance risks involved. Surely the law in your area prohibits unsafe excavations, attractive nuisances, and similar hazards to public safety.

As for Codes, all Building Codes are predicated on the idea that they exist for the main purpose of protecting the public health and safety ! Why else would they be written and adopted ?

My home course has two open ponds but they are not lined with PVC, they have gentle slopes and limited depths. Still, I'll bet the Course Owner pays considerable dollars in Insurance premiums every year.

good luck

 

[dicksewerrat]

How much volume will you lose when you put a couple feet of rip-rap on the sides so kids can get out. i wouldn't worry about a fox but the kids should be a major worry for the owner.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cub3bead]

Another alternative for an existing installation is to construct stairs on each bank so a person could climb out on their own. I assume a fox could eventually figure it's way out also.

 

[DarthSoilsGuy]

i've tried to find similar information, for preventative reasons. haven't found any recommendations for what the maximum slope you can put soil on an EPDM liner is, but anyway... this link contains a lot of code references. there isn't a smoking gun in it. but it references a lot of different state codes and guidelines. perhaps the name of the reference you need for the state work in is here for you to followup on.

http://www.udfcd.org/conferences/pdf/conf2006/5-1 Jones Safety Considerations.pdf

if the pond liner has to be replaced, a geosynthetic clay liner may be the way to go.

good luck

 

[DMcGrath]

Is the PVC liner smooth or textured? A colleague of mine "set the standard" so to speak after he went sliding down 90 meters of smooth HDPE liner at 3:1 slope. Fortunately he was not injured, but after that incident safety ropes were required. My point is, if someone goes in the pond, they will get wet. Wet PVC liner will be slick and very difficult to get out of regardless of slope.

If you can't replace the liner, perhaps apply a layer of another material on top. But if volume is a concern, how about something installed directly on the PVC for the purpose of aiding with traction, such as chain link fence fabric or something else with an aggressive traction capacity? Maybe a permanent Turf Reinforcement Mat (TRM) could be installed to provide traction and it may even grow some grass after a while. On the extreme end, a second layer of liner material such as Agru MicroSpike or SuperGripnet, laid "spikes up"? Might deter some animals along the way as well!

 

[cvg]

I would recommend leaving the bulk of it alone to save cost and maintain volume and provide either steps or a ramp at key locations