River with seven names – UNICA – Planinsko polje EarthCache

(SI) Planinsko polje je tipično kraško polje, z ravnim in pogosto poplavljenim dnom, ter reko, ki na enem koncu polja izvira, na drugem pa ponika. Najlepši primer prelivnega kraškega polja.

PRED ZACETKOM:
Opis tega Geološkega zaklada je dolg. Prosimo, preberite ga in si zapisite naloge za vpis se pred obiskom zaklada!

NALOGE ZA VPIS OBISKA
1. Struga Unice se od katavotronov nadaljuje se do naslednjih poziralnikov. V katero smer?
2a. Ocenite visino vode, ki je potrebna, da se prelije v katavotrone - visinska razlika od najnizje tocke dna recnega korita med obema katavotronoma do zgornjega roba nizjega katavotroma.
2b. Ce je struga napolnjena z vodo, ocenite visinsko razliko med zgornjim robom katavotrona in zgornjim robom recnega brega nad severnim katavotronom.
3. V skalni steni nad katavatronoma je vklesan napis v spomin na izvedena dela. Ocenite visino od katavotrona do napisa - do tja ob najvisjih poplavah sega voda!
4. Zelo bomo veseli, ce kaksno zanimivo fotografijo z mesta zaklada prilozite svojemu vpisu (logu) obiska.

POMEMBNO!
- Preden vpisete obisk zaklada, posljite odgovor preko GC profila ali neposredno na e-naslov vane.si.geo@gmail.com. Takoj potem lahko vpisete obisk zaklada na spletu – ne potrebujete dodatnega dovoljenja. Ce ste fotografirali, vpisu prilozite kaksno fotografijo.
- Vpisi brez ustrezne spremljajoce e-poste, ki vsebuje pravilne odgovore, bodo najprej trajno kodirani, kasneje izbrisani!
- Vpisi, ki vsebujejo odgovor bodo izbrisani!

(ENG) Planinsko polje is karst polje with flat, often flooded bottom and river which drains to polje at one end and sinks in ponors at the other. The best example of an overflow polje.

BEFORE THE BEGINNING:
This EarthCache has a long description! Please, read it and write down logging tasks before visiting the EarthCache site!

LOGGING TASKS
1. Unica river channel continues from katavotrons to next group of ponors. Into which direction?
2a. Estimate the height of water needed to start flowing into katavotrons - the height difference from lowest point of river channel between both katavotrons and upper edge of the lower katavotron.
2b. If the river channel was filled with water, estimate the height difference from katavotron edge and top of river channel bank near northern katavotron.
3. There is a memorial inscription on the cliff wall above katavatrons, made a long time ago. Guess height from katavotron to inscription - it is placed just about at the level of highest flooding!
4. We would be glad if you added interesting photos from the EarthCache location to your log.

IMPORTANT!
- Send answer through GC profile or directly to e-mail vane.si.geo@gmail.com before logging. After that you can log - you don't need an additional permission to log. Upload photos if you have taken them.
- Logs without an accompanying e-mail containing correct answers will be encrypted and later deleted!
- Logs containing the answer will be deleted!

(ENG) PLANINSKO POLJE
Ljubljanica is not just a short river from Vrhnika to river Sava! In fact, it is a mysterious river with at least seven names. It flows over Planinsko polje under a name Unica.

For easier undestanding, just short explanation of two scientific terms used in text:
POLJE ... Large flat-floored closed karst depression, with sharp slope breaks between the commonly alluviated floor and the marginal limestone. Streams or springs drain into poljes and outflow is underground through ponors.
PONOR ... Hole or opening in the bottom or side of a depression where a surface stream or lake flows either partially or completely underground into the karst ground-water system.

Planinsko polje is the last karst polje in the string of poljes in the system of river Ljubljanica. There is an entrance to Planina Cave in the pocket valley at the southern edge of the polje. Cave is well known especially because of underground confluence of two rivers: river Pivka, which flows form Postojna Cave and river Rak, which flows from Tkalca Cave and Rakov Skocjan valley. Thus river Unica is formed. Unica, enriched with some other springs meanders widely across the plain. Its channel is about 18 km long, almost four times as much as the longer axis of the polje. In the contact with soluble rocks at the north-eastern side of the polje Unica quickly loses water in many ponors. Main ponors are: Milavcevi kljuci, Pod stenami (Under the cliff) and Skofji lom. It is a very unusual experience to walk further and further from the river source at the time of average water level, and see less and less water in the river channel! Water sinks and flows underground towards sources of Ljubljanica near Vrhnika.
Planinsko polje is a perfect example of very well preserved karst polje. It is 5 km long and up to 2,5 km wide, encompassing about 10 sq km of land. The mean altitude is about 450 m. Polje is encircled with hills: Stari grad (703 m) and Kali (574 m) at south, Planinska gora (924 m) at west, low hills separate it from Ravnik at eastern side, low hills of Lanski vrh form the northern edge.

GEOMORFOLOGY AND HIDROLOGY
Planinsko polje owes its existence to Idrija tectonic fault. Polje is probably Holocene tectonic depression, formed as result of sinking between two parallel faults. Its edge is made of Cretaceous and Jurassic limestone, part of the bottom is Triassic dolomite in a narrow stripe from village Grcarevec, to Jakovica and towards south-eastern edge. Floor is covered with thin layer of clayey and sandy alluvium, just a few meters of thickness.


[Figure 2] Clipping form Geological Map of Slovenia, Geological Survey of Slovenia, 2009;
Rock formations of Planinsko polje and surroundings:
77: Thick-bedded Main Dolomite; Upper Triassic - Norian - Rhaetian (ca. 210 million years);
72: Micritic and oolitic limestone, limestone breccia and bituminous dolomite; Lower and Middle Lias (ca. 190 million years);
71: Micritic and oolitic limestone and bituminous dolomite; Upper Lias - Dogger (ca. 185 million years);
59: Thick-bedded micritic limestone and bituminous dolomite; Lower Cretaceous and lower part of Upper Cretaceous (ca. 130 million years);
57: Rudist and micritic limestone - Sezana Formation; Upper Cretaceous - Turonian (ca. 120 million years);
1: Fluvial sediments (gravel sand, silt and clay); Quaternary; (recent history);

AN OVERFLOW POLJE
Planinsko polje is the best example of an overflow polje in Slovenia. Short description of this type of poljes:
Flat-floored closed karst depression, with sharp slope breaks between the commonly alluviated floor and the marginal limestone. Streams or springs drain into poljes and outflow is underground through ponors. Commonly the ponors cannot transmit flood flows, so many poljes turn into wet-season lakes.

[Figure 3] Overflow polje in the area of porous or semi-porous rocks;

HIDROLOGY OF PLANINSKO POLJE
Water drains to polje from three sides. At the south, Unica is formed at the confluence of rivers Pivka and Rak inside of Planina Cave and drains to polje through pocket valley. The source of Unica has average annual flow rate of 24 m3/s (minimum 0,3 m3/s, maximum 100 m3/s). From another, large pocket valley Malenscica springs at Malni sources. Sktatovka springs at sources near ruins of Haasberg castle. Malni are filled with waters collected under Javorniki range and are an important potable water source for about 20.000 people.
Under village Grcarevec at north-western edge of polje, waters from Hrusica and Hotenje plains spring at high water levels. These waters then join meandering Unica, which sinks in limestone ponors at the north-eastern edge of polje. High water sinks into about 150 ponors, major part of it into ponors Pod stenami (Under the cliffs) at the north-east polje edge.
Planinsko polje is flooded several times each year. Maximal inflow of water to polje is from 100 do 120 m3/s, while ponors can drain away only from 40 to 60 m3/s! Polje is flooded up to two months annually, with water lever rising more than 10 meters in some places. The volume of the flood water is about 40 million cubic meters.
Water regulation and attempts of flood prevention have been made in the past, the most comprehensive under Viljem Putick after 1880. Therefore long sections of Unica modern water channel are actually artificially straightened. Even initial plans for an accumulation lake and underground pipeline towards Ljubljana moors, for a hydro-electrical power-plant have been made in the not-so-distant past. Luckily, such plans have been abandoned and Planinsko polje eventually protected as an important bird area of Natura 2000 network.

EARTHCACHE...
…coordinates are set near ponors Pod stenami (Under the cliff) at the northern edge of Planinsko polje. Among the ponors there, two largest stand out – their rocky shaft walls have been consolidated, upper edge surrounded by a low wall and opening covered with iron grate. Locals named those two strange objects Putick’s wells – after the manager of the amelioration works at the end of 19th century, Viljem Putick. Karst scientists decided to name this kind of device katavotron, which simply described ponor in old Greek. Nowadays katavotrons at Planinsko polje are a technical monument and even after more than hundred years they still serve the purpose – preventing ponors to clog with debris.

ACCESS
1. Most of the time, except at time of higher waters:
Starting at village Laze (waypoint No.1), follow road through village Jakovica, park your car at waypoint PARK, continue on foot along the cartroad, cross Unica river channel at waypoint No.2 (river-bed is dry there most of the time), continue to the crossroads (waypoint No.3), turn from track there and go straight to ponors across meadows.
2. When Unica flows all along its river channel to ponors Pod stenami:
Turn from paved local road Laze – Logatec to forestry road at waypoint No.4, follow the road westwards and leave car at PARK2. Turn to cartroad leading slightly uphill and then downhill towards south-east, follow track to waypoint No.3. Cross meadows to reach ponors.
3. At the time of flooding, there is NO ACCESS!
Roads and trails to EarthCache are public, there are no entrance fees.

Note: You use trails at your own risk. Use only trails you are fit to. Be safe and enjoy!
References:
- Ivan Gams, Kras v Sloveniji (Karst in Slovenia), ZRC Publishing, The Scientific research centre of the Slovenian Academy of Sciences and Arts, Ljubljana, 2004;
- Peter Skoberne, Ljubljanica od izvira do izliva (Ljubljanica from source to confluence), series Slovenija na dlani, Mladinska knjiga, Ljubljana, 2004;
- Karmen Peternelj, Thesis – Geomorphology of Planinsko polje, University of Ljubljana, Faculty of Arts, Department of Geography, Ljubljana, 2009;
- DEDI, Enciklopedy of Slovenian natural and cultural heritage web-site, Planinsko polje, authors of text: Andrej Mihevc, Natasa Ravbar, The Scientific research centre of the Slovenian Academy of Sciences and Arts);
- A Lexicon of Cave and Karst Terminology with Special Reference to Environmental Karst Hydrology, United States Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington Office, Washington, DC, EPA/600/R-02/003, 2002;

(SI) PLANINSKO POLJE
Ljubljanica ne tece samo od Vrhnike naprej. V resnici je to skrivnostna reka z najmanj sedmimi imeni. Pod imenom Unica se pretaka cez Planinsko polje.

Planinsko polje je zadnje, oziroma najnizje lezece, v vrsti kraskih polj sistema reke Ljubljanice. Na juznem robu polja je vhod v Planinsko jamo, ki je znana po preprosto dostopnem podzemnem sotocju dveh rek: Pivke, ki pritece iz Postojnske jame in Raka, ki pritece iz Rakovega Skocjana. Tako nastane Unica, ki se zdruzena z nekaj drugimi izviri, v stevilnih okljukih vije po ravnini. Zaradi meandriranja je struga Unice dolga 18 km ali skoraj stirikrat daljsa od dolzine polja. Na severovzhodnem delu polja Unica na stiku s prepustnimi apnenci naglo izgublja vodo na mnogih poziralnikih in ponorih. Glavni so: Milavcevi kljuci, Pod stenami in Skofji lom. Ob srednjem vodostaju je prav nenavadno, ker je v strugi vode vedno manj, bolj ko se oddaljujemo od izvira! Vode ponikajo in odtekajo proti izvirom Ljubljanice pri Vrhniki.
Planinsko polje je izrazito in zelo dobro naravno ohranjeno krasko polje. Dolgo je 5 km in siroko do 2,5 km. Ima priblizno deset kvadratnih kilometrov veliko ravno dno, ki lezi na nadmorski visini okrog 450 m. Polje na jugu zapirata hriba Stari grad (703 m) in Kali (574 m), na zahodu se pne Planinska gora (924 m), na vzhodni strani pa ga nizke vzpetine locijo od Logaskega ravnika. Na severni strani se dvigajo neizrazite vzpetine Lanskega vrha.

GEOMORFOLOSKA IN HIDROLOSKA VREDNOTA
Planinsko polje je nastalo ob idrijskem prelomu. Verjetno gre za holocensko tektonsko udorino, ki je nastala kot posledica pogrezanja med dvema vzporednima prelomnicama. Njegovo obrobje gradi zakraseli kredni in jurski apnenec, del dna pa triasni dolomit, ki se v ozkem pasu vlece od Grcarevca cez Jakovico in po dnu polja proti Uncu na jugovzhodu. Dno prekriva tenka, le nekaj metrov debela plast ilovnatih in pescenih naplavin.

PRELIVNO KRASKO POLJE
Planinsko polje je najlepsi primer prelivnega kraskega polja pri nas. Kratek opis taksnega tipa polj:
Vode se do polja pretakajo pod povrsino, skozi rove ustvarjene v vodoprepustnih kamninah. Na stiku z vodoneprepustnimi kamninami ali naplavinami na dnu kraskega polja, se del voda prelije na povrsje. V odvisnosti od kolicine vode, te bolj ali manj stalno vijugajo po povrsini polja, ob vecjih dezevjih pa ga tudi preplavljajo. Ko na obrobju dosezejo vodoprepustne kamnine, znova poniknejo. Polje ima sklenjen rob, pregib med dnom polja in obdajajocimi vzpetinami je oster.

HIDROLOGIJA PLANINSKEGA POLJA
Voda priteka na polje s treh strani. Na juzni strani priteka iz Planinske jame reka Unica, ki nastane z zdruzitvijo vodotokov iz Rakovega Skocjana in Pivske kotline. Izvir Unice ima povprecni letni pretok 24 m3/s (minimum 0,3 m3/s, maksimum 100 m3/s). Iz velike zatrepne doline priteka iz izvirov Malni Malenscica, iz izvirov pri razvalinah gradu Haasberg pa Skratovka. V Malnih privrejo na dan vode, ki se med cerkniskim in pivskim krakom Ljubljanice zbirajo pod Javorniki in so pomemben vir pitne vode za okrog 20.000 ljudi. Pod Grcarevcem, na severozahodni strani polja, ob visjih vodah izvirajo tudi vode iz Hrusice in Hotenjskega podolja. Na polju se pridruzijo vijugavi poti Unice, ki ob severovzhodnem robu polja ponika v apnenec. Ob visjih vodah ponika v okrog 150 poziralnikih; najvec vode odteka v ponore Pod Stenami na severnem robu polja.
Planinsko polje je poplavljeno veckrat letno. Maksimalni dotok vode na polje je od 100 do 120 m3/s, ponori pa jo lahko odvajajo le od 40 do 60 m3/s. Poplave trajajo do dva meseca na leto, voda naraste ponekod do 10 m, kolicina poplavne vode pa je okrog 40 milijonov m3. Poizkusi preprecevanja poplav so na vec mestih unicili naravno strugo Unice in poziralnike ob robu polja; najvec del je bilo opravljenih pod vodstvom Viljema Puticka po letu 1880. Bilo pa je tudi vec zamisli o akumulaciji vode na polju in o tunelu proti Ljubljanskemu barju za hidroelektrarno.

GEOLOŠKI ZAKLAD
Koordinate Geološkega zaklada so postavljene k poziralnikom Pod stenami, na severnem robu Planinskega polja. Med temi po velikosti izstopata dva, ki so ju konec 19. stoletja obzidali in prekrili s kovinskimi resetkami. Po vodji melioracijskih del in raziskovalcu toka kraske Ljubljanice, Viljemu Puticku, so jih domacini imenovali kar Putickove stirne. V krasoslovju uveljavljen izraz za taksno napravo je katavotron, beseda ki v starogrscini preprosto pomeni ponor. Katavotrona danes veljata za tehnicni spomenik in tudi po vec kot sto letih se vedno preprecujeta zatrpavanje poziralnikov s plavjem.

DOSTOP
1. Vecji del leta, razen ob visjih vodah:
Iz vasi Laze (waypoint No.1) po cesti skozi vas Jakovica, parkirate avto na tocki PARK, nadaljujete pes po kolovozu, preckate strugo Unice (waypoint No.2), po kolovozu nadaljujete do krizisca (waypoint No.3) in po brezpotju preko travnikov do poziralnikov.
2. Kadar je struga Unice polna vse do poziralnikov Pod stenami:
S ceste Laze – Logatec zavijete na gozdno cesto na tocki 4 (waypoint No.4), sledite ji na zahod, na tocki PARK2 pustite avto in zavijete na kolovoz, ki vodi najprej rahlo navzgor, potem pa navzdol proti jugovzhodu. Od tocke 3 (waypoint No.3) preko travnikov do poziralnikov.
3. Ob visoki vodi, ko je polje poplavljeno, NI DOSTOPA!

Opomba: Poti uporabljate na lastno odgovornost! Hodite le po poteh za katere ste ustrezno pripravljeni! Zelimo vam varno pot in veliko uzitkov!
Viri:
- Ivan Gams, Kras v Sloveniji v prostoru in casu, Zalozba ZRC, Znanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti, Ljubljana, 2004;
- Peter Skoberne, Ljubljanica od izvira do izliva, zbirka Slovenija na dlani, Mladinska knjiga, Ljubljana, 2004;
- Karmen Peternelj, Diplomsko delo - Geomorfologija Planinskega polja, Univerza v Ljubljani, Filozofska fakulteta, oddelek za geografijo, Ljubljana, 2009;
- DEDI, Enciklopedija naravne in kulturne dediscine na slovenskem, Planinsko polje, avtorji zapisa: Andrej Mihevc, Natasa Ravbar (Institut za raziskovanje krasa, Znanstvenoraziskovalni center Slovenske akademije znanosti in umetnosti);
- A Lexicon of Cave and Karst Terminology with Special Reference to Environmental Karst Hydrology, United States Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington Office, Washington, DC, EPA/600/R-02/003, 2002;