HYDROCAD - Mounding for Infiltration Basins
HYDROCAD - Mounding for Infiltration Basins
(OP)
Hello,
We usually do not get involved with mounding analysis for our infiltration basin designs - unless required by the reviewing engineer.
Our NJ state requirement for infiltration basins is to have a 2 foot separation to groundwater, and to "halve" the percolation rates of the soil for the design.
Our geotechnical engineer has followed the simple USGS mounding analysis spreadsheet available here:(http://pubs.usgs.gov/sir/2010/5102/)and tells me that the mound of water is 9 feet in the center of the basin and that the basin will overtop and it fails.
My question is, doesn't the HYDROCAD program take into account the impact of the underlying groundwater on the basin's ability to infiltrate? The HYDROCAD program asks me for the infiltration rate of the soil, the separation to seasonal high GW, and when I input the 100 year storm. Usually when the program tells me that the water reaches a certain level during the 100 year storm, that's as far as we go.
Does this mean that we've been designing basins without looking at the other half of the puzzle for all of these years, or is the geotechnical engineer completely wrong?
I feel that the two programs are calculating two different things, but I don't know enough to discuss intelligently with the geotech engineer.
We usually do not get involved with mounding analysis for our infiltration basin designs - unless required by the reviewing engineer.
Our NJ state requirement for infiltration basins is to have a 2 foot separation to groundwater, and to "halve" the percolation rates of the soil for the design.
Our geotechnical engineer has followed the simple USGS mounding analysis spreadsheet available here:(http://pubs.usgs.gov/sir/2010/5102/)and tells me that the mound of water is 9 feet in the center of the basin and that the basin will overtop and it fails.
My question is, doesn't the HYDROCAD program take into account the impact of the underlying groundwater on the basin's ability to infiltrate? The HYDROCAD program asks me for the infiltration rate of the soil, the separation to seasonal high GW, and when I input the 100 year storm. Usually when the program tells me that the water reaches a certain level during the 100 year storm, that's as far as we go.
Does this mean that we've been designing basins without looking at the other half of the puzzle for all of these years, or is the geotechnical engineer completely wrong?
I feel that the two programs are calculating two different things, but I don't know enough to discuss intelligently with the geotech engineer.





RE: HYDROCAD - Mounding for Infiltration Basins
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HYDROCAD - Mounding for Infiltration Basins
If you continue to hope for infiltration after this 6 inches has perc'd into the soil, then water has to get out of the way! That requires horizontal flow and a horizontal flow gradient - i.e., mound.
These infiltration facilities have all be conceptualized by drainfield designers with very little thought on ground water hydrology.
It's time to get it right!
f-d
ípapß gordo ainÆt no madre flaca!
RE: HYDROCAD - Mounding for Infiltration Basins
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: HYDROCAD - Mounding for Infiltration Basins
Current testing uses a perc test where a pit is dug and filled with water. I have always thought that this approach over estimated infiltration rate. I prefer the double ring test that is used to derive the Infiltration curve. I presume the double ring includes influence from mounding that is typically derived from a double ring infiltration test. What do you thing, does the double ring account for mounding?
RE: HYDROCAD - Mounding for Infiltration Basins
Fortunately, kh is usually 2 to 4 times greater than kv.
f-d
ípapß gordo ainÆt no madre flaca!
RE: HYDROCAD - Mounding for Infiltration Basins
Water just can't get out of the way fast enough to offset the vertical recharge - hence the mound. . .
f-d
ípapß gordo ainÆt no madre flaca!