Gauge pressure of a dam? please help?

Question

1) A reservoir behind a dam is 31 m deep. What is the gauge pressure at the base of the dam? The acceleration of grav-
ity is 9.8 m/s^2 and atmospheric pressure is
10100 Pa... Answer in units of kPa.

2) What is the gauge pressure 11 m from the top
of the dam? Answer in units of kPa.

Answer 1

For pressure due to a column of fluid
P = density * g * H
Atmospheric pressure, at least where I live, is 101.3 kPa

Assuming dam holds fresh water, density is 10^3 kg/M^3
Don't need atmospheric pressure since question is gauge pressure not absolute

1] P = (1000 kg / M^3)(9.8 M / S^2) (31 M) = roughly 310 kPa = roughly 3 atmospheres
2] Same problem as 1, just use 11 instead of 31

Answer 2

Gauge pressure is absolute pressure minus atmospheric pressure. P = ghρ, where h is height of the water column and ρ is density. Density of water is 1000 kg/m^3. Go figure, for h=31 and h=11. Answers are in Pa.