Water is flowing at a steady rate through a homogeneous and saturated horizontal soil strip of $10$ m length. The strip is being subjected to a constant water head $(H)$ of $5$ m at the beginning and $1$ m at the end. If the governing equation of flow in the soil strip is $\dfrac{d^2H}{dx^2}=0$ (where $x$ is the distance along the soil strip), the value of $H$ (in m) at the middle of the strip is _______