Hillslope function

[changliao1025]

After the subbasin is defined, we can add the hillslope for each subbasin.
We can use the last reach angle to define left or right.

[changliao1025]

In order to allow each subbasin to define hillslope, the subbasin must be linked to its main channel.

[changliao1025]

The definition of hillslope requires the information from segment, then the characteristics of segment must be called first.

So the hillslope definition must be called within or after the characteristics function.