This Instruction establishes the modalities of subdivision of the national territory into hydrographic units – river basins (basin level) and sub-basins (sub-basin level). It establishes: (a) principles and criteria of subdivision into hydrographic units; (b) modalities of determination and description of boundaries of hydrographic units; and (c) composition of the documentation for validation of the number of hydrographic units and boundaries thereof. This Instruction shall be used as guideline