Hydrological code

A hydrological code is a sequence of numbers or letters that identify a hydrological feature like a River, Lake, Watershed, Catchment or Riversegment. Several hydrological codes are existing. Each having specific characteristics in accordance with a specific use.The code developed by Strahler orders catchments with respect to the number of tributaries upstream or a certain riverstrech. The hydrological code of Pfafstetter identifies riversegments along the longest flow path, and subsequently allows for identification of the position of the riverstrech in the Watershed

A Comprehensive coding system is in use in Europe. This system codes from the Ocean to the so-called primary catchment. The system determines a set of Oceans of Endorheic systems identified by a letter. The systems are subdivided by Seas. The seas are numbered 1 to 9. Seas lying far from the Ocean, for example the Black Sea receive a higher number.The Seas are limited using the so-called definitions made by the international Hydrographic Organisation in 1953. The coasts of these seas are defined clock wise from north west to south east from the Strait where the sea connects to the Ocean or the other seas. Subsequently every Watershed along this coast gets a number using the so-called Pfafstetter logic. The implies that the four largests watersheds are selected and receive numbers 2,4,6 or 8. The watersheds inbetween the large systems receive numbers 3,5 and 7. Numbers 1 and 9 are used for the small watersheds on the egdes of the strait. The smaller systems can subsequently be numbered recursivily or kept together for grouping purpose.