Change Reservoir model default h_0 value to 0 (zero).

[boerrebj]

With the new elevation model, setting z_0 will probably be the more normal use. Forgetting to set h_0 to 0 will give wrong values.

[dietmarw]

I'm not sure this is correct. having h_0 set to 0 basically means you are placing the intake on the surface. And that would be unrealistic.