Best Of

Hi Ryan, thanks for reaching out. The discrepancy comes from the fact that Model 1 gets its water conditions from SEEP/W and Model 2 gets its water conditions from a piezometric line. SLOPE/W tends to overestimate the pore-water pressure when the phreatic surface is defined with a piezometric line that is downward sloping (to represent downward flow), which is usually the case in an embankment. This is because it uses the vertical distance from the base of a slice to the phreatic surface to calculate the pore-water pressure.

When SLOPE/W uses the water conditions calculated with SEEP/W, the pore-water pressure values at the base of the slices are more accurate. In the case of a downward sloping phreatic surface, the pore-water pressure used in SLOPE/W will be lower due to the equipotential lines being angled. I've set up an example where you can see that even on the upstream slope of the dam, the equipotential lines are different. The first picture is with the drawn piezometric surface and the second picture is with the SEEP/W pore-water pressure conditions.