Small watersheds are parts of a larger watersheds as small streams or rivers drain in larger ones. Thus, watersheds show an order according the river order.
The tributaries of the Gina River drain small watersheds (see figure). These are the subbasins of the Gina River catchment (17).
As the Gina River is a third order tributary of the Hare River this small Gina River catchment is part of the larger Hare River catchment. The Hare River, in turn, is part of a larger basin – the Abaya-Chamo basin, named after its two major lakes which are hydrologically interconnected by a spillway. This basin includes several other sub-basins. And again, the Abaya-Chamo basin is a sub-basin of the Rift Valley Lakes basin.
'Why watersheds are a reasonable planning unit' is explained on the next learning page.