The relationship between the length scale ratio $(L_r)$ and the velocity scale ratio $(V_r)$ in the hydraulic models, in which Froude dynamic similarity is maintained is:
1. $V_r=L_r \\$
2. $L_r=\sqrt{V_r} \\$
3. $V_r= L_r^{1.5} \\$
4. $V_r=\sqrt{L_r}$