Plains-fed rivers originate in the plains, fed by sub-surface flow from the alluvium. The Burhi Gandak is an example again smaller in area and discharge, entirely confined to the alluvial plains and therefore having an upland source area to alluvial area ratio of zero.

The Burhi Gandak originates in the upper plains of the west Champaran district of northern Bihar. Historical evidence indicates that the main Gandak channel belt followed the course of the present Burhi Gandak until about 100 years ago. In other words, the Burhi Gandak is a minor plains-fed river occupying the position of a former, much larger, mountain-fed river. There may be some overbank connection with the main Gandak channel at times of high flood, but it appears to receive most of its water from minor tributarie and floodplain sheet flow in the plains. The Burhi Gandak is not braided in any reach between its source area and its confluence with the axial Ganga.