The Gewässerkennzahl (GKZ, rarely GWK or GEWKZ) or "waterbody index number/waterbody number" is an identifier with which all watercourses in Germany are numbered, together with their catchments and precipitation areas. It is also referred to as a Gebietskennzahl or "basin number". A Gewässerkennzahl may have up to 13 figures (theoretically even 19). Basins normally are only defined up to seven figures. For a more detailed subdivision, the Gewässerkennzahl may be enlarged by ten more figures. Only that enlarged version is called Fließgewässerkennziffer. The Gewässerkennzahlen are defined by the environment offices of the states.
History In order to have comparable values and usable data across the state of Germany, the Federal and State Water Authorities agreed in December 1970 to create a unified system for hydrological work on certain important rivers and their above-ground catchment areas and to issue them with index numbers. Linked to that was the establishment of the size and boundaries of their catchment areas.
Principle Every waterbody (streams, rivers, canals and ditches, but also lakes and even some bays) and its catchment area was given a waterbody number in such a way that it could be clearly identified. The waterbody numbers are built in hierarchical fashion so that, based on the number, the next river system of the waterbody can be deduced.
Scheme At first the course of water has to be defined from source to mouth. Then the four major tributaries (or 'affluents') are identified. They are marked by even figures in downstream sequence, "-2, -4, -6, -8". This way, the (main) course is divided into five sections, which are marked by odd figures, "-1, -3, -5, -7, -9". A number with an even end-digit is the number of a whole watercourse, while a number with an odd end-digit is the number of a section. Lowest sections are always given a nine, even if not all figures between one and nine have been used. In the next step of numbering, each section defined by the first step is dealt in the same way, selecting four major tributaries and marking five sections.
Lakes Lakes are integrated as a part of the watercourse formed by their main tributary and their outlet.
Coastal regions For coastal regions, the scheme of numbering was altered in different ways by different states: Lower Saxony left the rule of using only odd numbers for sections. Nevertheless, bay as dependent waterbodies got even numbers. Mecklenburg-Vorpommern stuck to using even numbers for important rivers and odd numbers for – here coastal – sections in between. But the course of the coast was defined in a way, that in two straits different third figures were used for their two banks.
Waterbodies without a Gewässerkennzahl Some waterbodies indexed under this classification system have un-indexed headstreams or lateral tributaries in the form of very small streams or ditches. If such an unclassified waterbody is relevant for the water management of the region, it may be given a number within the local classification system of the regional Wasser- und Bodenverband (association for water and ground management).
Catchment areas The numbers for a watercourse and its catchment area are thus identical. If a river has subsidiary watercourses, an additional figure is allocated to its index number for each further branch. So in theory even a rivulet could be allocated its own catchment. In practice, catchment numbering for water sources below the level of streams is not used.
Catchment areas are thus distinguished by a number with up to a maximum of seven digits. Watercourse index numbers, by contrast, may have up to 13 digits in order to be able to classify all their tributaries and headstreams; although in practice only 10 digits are used.
Main river systems The first digit of the number indicates which major river basin the waterbody belongs to, as follows: 1 Danube 2 Rhine 3 Ems 4 Weser 5 Elbe 6 Oder 9 Coastal region
The second and subsequent digits of the index number represent further subdivisions of the river and its catchment area.
Example The Heusiepen stream in Remscheid has waterbody number 27366462. This can be decoded as follows:
Main stem system / catchment area Rhine (2) → River system / catchment area Wupper (2-736) → River system / catchment area Morsbach (2-736-6) → River system / catchment area Gelpe (2-736-6-4) → River system / catchment area Saalbach (2-736-6-4-6) → Stream without defined catchment area Heusiepen (2-736-6-4-6-2)
Waterbody index numbers Listed below are all the rivers with up to a three-figure index number, and some rivers with four-figure numbers above a length of 50 km.
1 Danube
Number Name Length[km] Catchment area[km²] 1 Danube (including the Breg) 2857 817,000 112 Lauchert 60.3 456 114 Iller (including the Breitach - Turabach) 147 2,147 1158 Günz 55 710 116 Mindel 81 962 1172 Brenz 52 880 118 Wörnitz 132 1,686 12 LechLFU Bayern, Gewässerverzeichnisse → Lech (PDF) 264 3,926 122 Archbach (river totally in Austria, basin partly in Germany) 10 145 124 Vils 36 198 126 Wertach 150 1,260 128 Lechkanal 14 19 132 Friedberger Ach (with Hagenbach–…–Verlorener Bach) 100 598 LfU Bayern, Gewässerverzeichnisse → Flussgebiet Lech bis Naab 134 Paar 134 1,632 136 Abens 72 1020 138 Altmühl 234 2,251 14 Naab (including the Waldnaab) 165 5,432 142 Haidenaab 60 714 144 Pfreimd 56 595 146 Schwarzach 80 822 148 Vils 78 1,100 152 Left branch of Danube in Regensburg 3,6 2.881 LfU Bayern, Gewässerverzeichnisse → Donau von der Naab bis zur Isar 1522 Regen (including Black Regen - Great Regen) 191 2,953 154 Pfatter 37 262 156 Große Laber 75 407 158 Kinsach–Ferchenbach 38 317 16 Isar 295 8,370 162 Loisach 113 954 164 Amper (with Ammer, Linder, Fischbach, Rückentalbach) 209 3,248 166 Mittlerer Isarkanal (Middle Isar Canal) 64,7 1,147 168 Plattlinger Mühlbach (with Längenmühlbach) 75 345 172 Hengersberger Ohe (with Ranzinger Bach) 34 198 174 Vils (including the Große Vils) 110 1,445 176 Große Ohe (with Geißa–…–Geißleitenbach) 46 176 178 Ilz 62 850 18 Inn 517 26,130 182 Mangfall (including the Weißach) 58 1,099 184 Alz (including the Tiroler Achen) 150 2,197 186 Salzach 225 6,700 188 Rott 109 1,205 1914 Große Mühl 71 560
2 Rhine
Number Name Length[km] Catchment area[km²] 2 Rhine 1239 185,300 215 Lake of Constance: Obersee (GKZ: 215 – 217)5,386 217 Lake of Constance: Untersee; also including the section of the Rhine down to its confluence with the Thur 2152 Argen with Obere Argen 73 655 2198 Wutach 91 1,140 232 Wiese 55 458 2338 Elz 121 1,539 234 Kinzig 93 1,406 236 Murg 80 466 238 Neckar 362 13,934 2382 Fils 63 699 2384 Enz (including Poppelbach and Great Enz) 106 2,229 2386 Kocher (including the Black Kocher) 169 1,960 2388 Jagst 190 1,838 24 Main (including the White Main) 572 27,292 242 Regnitz (including the Rednitz and Franconian Rezat) 187 7,523 2422 Pegnitz (including the Fichtenohe) 127 1,230 244 Franconian Saale 139 2,765 246 Tauber 129 1,810 248 Nidda 90 1,942 252 Selz 61 389 254 Nahe 125 4,067 256 Wisper 30 209 258 Lahn 246 5,925 26 Moselle 544 28,286 262 Sauer 173 4,259 264 Saar 235 7,431 2642 Blies 99 1,960 2646 Prims 91 737 2648 Nied (including the Nied Française) 114 1,370 266 Kyll 142 845 268 Alf 52 358 2716 Wied 102 771 2718 Ahr 85 897 272 Sieg 155 2,857 2736 Wupper 116.5 813 274 Erft 107 1,838 276 Ruhr 219 4,485 2772 Emscher 83 775 278 Lippe 220 4,888 28 Meuse (river totally outside Germany, basin partly in Germany) 874 33,000 282 Rur 165 2,361 284 Schwalm 35 268 286 Niers 118 1,381
3 Ems Here some three-figure numbers are not listed. Number Name Length[km] Catchment area[km²] 3 Ems 371 13,160 316 Hessel 39 213 318 Bever 39,5 217 32 Werse 67 762 332 Münstersche Aa 43 172 34 Große Aa 25 922 36 Hase 170 3,086 38 Leda (with Ohe u. Sagter Ems) 75 1.917 388 Jümme (with Barßeler Tief & Soeste) 94 450 394 Oldersumer Sieltief (with Fehntjer Tief (North) & western Flumm) 26 235 397 Dollard (as a section of Ems estuary) 3974 Dollard (as a bay of Ems estuary) 398 Knockster Tief (with Wiegoldsburer Riede) 31 1351 399 Outer mouth of Ems River
4 Weser
Number Name Length[km] Catchment area[km²] 4 Weser (from confluence of Werra and Fulda) 451 41,094 41 Werra 300 4,497 412 Hasel 26 331 414 Ulster 57 421 416 Hörsel 55 784 418 Wehre 36 452 42 Fulda 221 6,947 422 Fliede 22 271 424 Schlitz (river) (including Altefeld, own GKZ 4241) 43 315 426 Haune 67 500 428 Eder 176 3,361 432 Schede 13 49 434 Nieme 17 40 436 Schwülme 29 290 438 Reiherbach 10.5 35 44 Diemel 111 1.762 442 Hoppecke 35 92 444 Twiste 41 447 446 Warme 33 157 448 Esse 28 192 452 Nethe 50 460 454 Lenne 24 125 456 Emmer 62 535 458 Exter 26 109 46 Werre 72 1,485 462 Bega 44 377 464 Aa (including Johannisbach) 44 377 466 Else 35 416 468 Rehmerloh-Mennighüffer Mühlenbach 16 71 472 Bückeburger Aue 39 173 474 Gehle 27 163 478 Steinhuder Meerbach 29 356 476 Große Aue 85 1,522 48 Aller 260 15,744 482 Oker 128 1,834 484 Fuhse 98 918 486 Örtze (including Aue & Wietze) 70 760 488 Leine 281 6,512 492 Ochtum (including Süstedter Bach) 45 917 494 Wümme 118 1.585 496 Hunte 189 2,785 498 Lune 43 383 Umwelt Niedersachsen – Liste Weser
5 Elbe
Number Name Length[km] Catchment area[km²] 5 Elbe 1094 148,268 52 Vltava (river totally in Czechia, basin partly in Germany) 430 28,090 5281 Mže 103 1,829 532 Ohře 316 5,614 538 Black Elster 179 5,705 54 Mulde (Zwickau + United Mulde) 314 7,400 541 Zwickau Mulde 167 2,352 542 Freiberg Mulde 124 2,981 549 Vereinigte Mulde (United Mulde) 147 7,400, own 2,067 56 Saale 413 23,719 562 Loquitz 34 364 564 Unstrut 192 6,364 566 White Elster 257 5,154 568 Bode 169 3,229 572 Nuthe 39 509 574 Ehle 40 ? 576 Ohre 103 1.503 578 Tanger 33 480 58 Havel 334 23,858 582 Spree 400 10.100 584 Nuthe 52 1,935 586 Plane 57 639 588 Rhin 129 1,780 592 Elde 208 2,990 5934 Jeetzel 73 1.928 594 Ilmenau 107 2,852 5956 Alster 56 581 5958 Este 62 364 596 Lühe (including Aue) 44 216 5974 Stör 78 1.781 598 Oste 153 1,711
6 Oder
Number Name Length[km] Catchment area[km²] 6 Oder 866 118,861 674 Lusatian Neiße 254 4,297 696 Western Oder 17 (in Germany)
9 Coastal region
Number Name Length[km] Catchment area[km²] 928 Issel 82 1,208 934 Western Ems 94 Coastal seas between Borkum and Sahlenburg mudflat 942 Jade Bight 95 Coastal seas between Sahlenburg mudflat and the Danish Border 952 Eider 188 3,275 96 Baltic Sea 962 Trave 114 2,676 964 Warnow 155 3,324 9652 Recknitz 88 669 966 Peene 136 5,110 9664 Tollense 96 1,829 9666 Trebel 87 956 968 Uecker (upper section Ucker) 98 2,200
Literature Landesamt für Wasser und Abfall Nordrhein-Westfalen (publ.): Gebietsbezeichnung und Verzeichnis der Gewässer in Nordrhein-Westfalen
See also Waterbody index number – an overview Stream order, hydrological hierarchy of rivers and streams
References
External links Bund-Länder Arbeitsgemeinschaft Wasser (LAWA) Erläuterung der Gewässerkennzahl im Bayerischen Landesamt für Umwelt