From sub- + basin.
subbasin (plural subbasins)
- (geography) A basin within a larger basin.
2009 May 14, Felicity Barringer, “Rising Calls to Regulate California Groundwater”, in New York Times[1]:Since 2006 the surface of the aquifer, in the Kaweah subbasin of the San Joaquin basin, has dropped 50 feet as farmers pumped deeper, Mr. Watte says.
