(1) Basin permitting the study of the hydrological cycle in a characteristic natural region by the simultaneous observation of climatic and hydrometric data. (GHP)
(2) Basin where intensive hydrological studies are conducted under relatively unchanged conditions.
(3) Basin in which hydrological stations are installed to make simultaneous hydrometeorological and hydrometric observations so that the measurements would represent a broad area in lieu of making measurements on all basins in a given region.
UNESCO/WMO International Glossary of Hydrology (2nd revised ed., 1992)