Three soil specimens (Soil $1$, Soil $2$ and Soil $3$), each $150$ mm long and $100$ mm diameter, are placed in series in a instant head flow set-up as shown in the figure. Suitable screens are provided at the boundaries of the specimens to keep them intact. The values of coefficient of permeability of Soil $1$, Soil $2$ and Soil $3$ are $0.01, \: 0.003$ and $0.03$ cm/s, respectively.

The value of $h$ in the set-up is

1. $0$ mm
2. $40$ mm
3. $255$ mm
4. $560$ mm