SWM Facility - High Water Table and Fine Sand Subgrade

[Luke_Water Resources]

Hello,

I am curious if anyone has experience with designing a wet pond in a saturated groundwater condition with soil consisting of fine sand. I want to limit armouring and lining material to make it as economical as possible. After reviewing this chart (attached below), I see the stable slopes for fine sand under active and still water conditions. Do you think the annual groundwater interaction with the permanent pool level can be classified as still water? or is this too risky?

Thanks for any help on this!

-Luke

 

[SlideRuleEra]

Do you think the annual groundwater interaction with the permanent pool level can be classified as still water? or is this too risky?

I consider the assumption of still water too risky. A large bottom ash ponds for one of our coal-fired electric generating stations was about 18 feet deep, with 9 feet of that depth being below the water table. However, we used a geosynthetic bentonite liner for the entire 18 ft. depth for ground water pollution control. Over time, wind action on the pond's surface caused wave action, which is not still water.

If your assumption of still water happens to be be wrong, even if just occasionally, having the dike slope start changing from 1:3.7 to 1:11.4 will be not be something easy to correct.

 

[swazimatt]

if the bank is planted and/or grassed does the table still apply?
There are options for "armoring" planted banks with fine geogrids

 

[gbam]

Curious, does that table assume 100% saturation? I recommend involving the geotechnical engineer to document the saturated under water stable slope in their sealed report. That is how we approach design of retention/detention basins.