Watershed Management

A watershed has a total drainage basin area of $50.0\text{ km}^2$. The sum of lengths of all mapped stream channels of all orders is $\sum L = 125.0\text{ km}$. The drainage density ($D_d = \frac{\sum L}{A}$) in $\text{km/km}^2$ is ________ (round off to 1 decimal place).