Irrigation Water Conveyance and Application Methods

During an irrigation event, water depths stored at four equidistant sampling locations along a furrow run are $80\text{ mm}$, $100\text{ mm}$, $120\text{ mm}$, and $100\text{ mm}$. Calculate the water distribution efficiency ($\eta_d = 100 \left[1 - \frac{\bar{y}}{\bar{d}}\right]$) in percentage, where $\bar{d}$ is the numerical average depth and $\bar{y}$ is the average absolute deviation from $\bar{d}$.