The correct statements about the phreatic line in an earth dam are:

1. The phreatic line is approximately a parabola.
2. The phreatic line is the top-most flow line with zero water pressure.

Now let's understand what the phreatic line represents and why these statements are correct.

**Phreatic Line:**
The phreatic line, also known as the groundwater table, is the boundary between the saturated zone and the unsaturated zone in the ground. In the case of an earth dam, the phreatic line represents the level of groundwater within the dam.

**Statement 1: The phreatic line is approximately a parabola.**
When an earth dam is constructed, the water level behind the dam rises, creating a water pressure distribution within the dam. The shape of the phreatic line depends on the geometry of the dam and the seepage conditions. In the case of an earth dam, the phreatic line is generally curved and can be approximated as a parabola.

The parabolic shape of the phreatic line is a result of the flow of water through the dam. The water flows through the dam due to seepage and follows a curved path. This curved path creates the parabolic shape of the phreatic line. The curvature of the phreatic line is influenced by various factors such as the permeability of the dam material, the slope of the dam, and the hydraulic gradient.

**Statement 2: The phreatic line is the top-most flow line with zero water pressure.**
The phreatic line represents the level of groundwater within the dam. It is an equipotential line, which means that the water pressure is constant along the line. The phreatic line is the top-most flow line with zero water pressure because it represents the point where the water pressure becomes zero.

As the water flows through the dam, it follows the path of least resistance, which is along the phreatic line. The water pressure decreases as it moves away from the phreatic line. At the phreatic line, the water pressure is zero, and beyond that point, the water pressure is negative (i.e., suction pressure). Therefore, the phreatic line represents the top-most flow line with zero water pressure.

In conclusion, the correct statements about the phreatic line in an earth dam are that it is approximately a parabola and it is the top-most flow line with zero water pressure.