Matsayi na wuka

A cikin ilimin ƙasa, k**nickpoint** ko nickpoint (knick da aka karɓa daga Jamusanci Knick, juyawa mai kaifi) wani ɓangare ne na kogin ko tashar inda akwai canji mai mahimmanci a cikin gangaren gadon tashar, kamar ruwa ko tafkin. Knickpoints suna nuna yanayi da matakai daban-daban a kan kogi, sau da yawa ya haifar da rushewa da ta gabata saboda glaciation ko bambancin lithology. A cikin sake zagayowar samfurin rushewa, knickpoints suna ci gaba da sake zagayolar sama, ko ciki, maye gurbin tsohuwar sake zagayowarsa. Wani knickpoint wanda ke faruwa a kai (mafi girma) na tashar ana kiransa headcut. Headcuts da ke haifar da rushewar kai sune alamun fasalulluka masu tasowa irin su rushewar gullies.

Knickpoints kuma suna faruwa a kan wasu jikin duniya waɗanda a baya suna da ko a halin yanzu suna da ruwa, wato Mars  da Titan.  A kan Mars, knickpoints suna da tsawo na yau da kullun wanda ke ba da shawarar matakin teku na yau da kullum don tsohuwar teku ta Martian. A Titan, kwarin tsaunuka da ke kusa da Tekun hydrocarbon na yanzu suna nuna shaidar knickpoints da Canjin matakin teku na baya-bayan nan.

## Kafawa
An kafa Knickpoints ta hanyar tasirin tectonics, tarihin yanayi, da / ko lithology. Misali, hauhawa tare da kuskuren da kogi ke gudana sau da yawa zai haifar da kaiwa mai zurfi tare da tashar, wanda aka sani da *knickzone*. Glaciation wanda ke haifar da kwarin da ke rataye sau da yawa sune manyan wurare don maki. Idan lithology na dutsen ya bambanta, kamar shale tsakanin dutsen igneous, rushewa zai faru a hankali a cikin dutse mai laushi fiye da ke kewaye da shi, dutse mai ƙarfi.

Matsayi na asali shine tsawo na saman ruwa wanda kogi ya shiga, yawanci teku. Raguwa a matakin tushe yana haifar da martani ta hanyar tsarin kogi don sassaƙa cikin wuri mai faɗi. Wannan yankan ya fara ne a lokacin da aka kafa wani cuckpoint, kuma ƙaura ta sama ta dogara sosai da yankin magudanar ruwa (da kuma fitar da kogi), kayan da yake yankewa, da kuma girman saukowa a matakin tushe.

## Misalai na zamani

Knickpoints sun hada da magudanan ruwa da wasu tabkuna. Wadannan fasalulluka sun zama ruwan dare a cikin koguna tare da isasshen gangaren, watau isasshen canji a tsawo sama da matakin teku akan tsawon su don ƙarfafa lalacewa.

### Tasirin lithology
Bambance-bambance a cikin kwanciyar hankali na dutsen da ke ƙarƙashin tasirin ci gaban kogin da ke cikin dutse, yayin da ruwa ke lalata nau'ikan dutse daban-daban a ƙididdiga daban-daban. Victoria Falls, a kan Kogin Zambezi, misali ne mai ban mamaki na wannan. gorges da ake gani ta hanyar hotunan tauraron dan adam suna nuna hanyoyin rushewa a bayan kafa faduwar. A nan, yawancin dutsen saman babban dutse ne, tare da manyan tsagewa cike da dutse mai sauƙin iska wanda aka gani ta hanyar Zambezi a fadin ƙasar. Kogunan da ke ƙasa da faduwar da yake gudana sun lalace a tsawon lokaci ta hanyar aikin ruwa.

### Tasiri daga aikin tectonic
A ko'ina cikin New Zealand, haɓakar tectonic da lalacewa suna ba da gudummawa sosai ga farawa da koma baya. An yi nazarin Tsarin Kogin Waipoua, a tsibirin Arewa kuma an yi amfani da shi don ƙirƙirar samfuran lissafi don hango hasashen halayyar knickpoints. Binciken ya nuna alaƙa kai tsaye tsakanin yankin da ke sama da yawan ƙaura, samar da bayanan da aka tsara kusa da bayanan da suka tattara. Tsarin Kogin Waipoua yana yankewa ta hanyar turɓaya, a mafi yawancin, sabanin dutse.

### Tasirin aikin kankara

Canje-canje masu tsawo a cikin gangara sun zama ruwan dare a cikin koguna da ke gudana ta hanyar shimfidar wuri da aka bari a baya lokacin da glaciers suka koma baya. Kwarin kankara, da kuma isostatic rebound wanda ya haifar da cire Kwarin kankara na kankara yana taimakawa ga wannan.

Niagara Falls, a kan iyakar Amurka da Kanada, misali ne na musamman na knickpoint. Faduwar ta ragu a cikin ƙaura daga kusan 1m a kowace shekara tun daga 1900 zuwa 10 cm na zamani a kowace shekara. Ruwan, musamman Horseshoe Falls, suna da tsayi sosai kuma sun haifar da glaciation. Babban Tafkuna da kansu suna kwance a cikin rugujewar da ƙanƙara suka bari, yayin da ɓawon burodi ke ci gaba da sakewa.&nbsp;

Bridalveil Fall, a cikin Yosemite Valley, California, ya zubo a kan bakin kwarin da ke rataye.

## Paleomorphology

Za'a iya adana shaidar wani cuckpoint a cikin yanayin da ya gabata a cikin siffar dutse a ƙasa da duk wani ajiya na gaba, da kuma a cikin ajiyar sedimentary da mutum ko wani aiki bai canza ba. Tafkunan suna cikawa da laka a tsawon lokaci, amma magudanan ruwa galibi suna lalacewa. Akwai 'yan misalai masu banƙyama, har yanzu ana iya ganinsu a yau na wuraren da aka yi amfani da su kafin tarihi.

### Shaidar ambaliyar ruwa mai yawa
Dry Falls, wani dutse mai tsawon 3.5 mi a tsakiyar Washington, misali ne na tsohuwar knickpoint. Shaidar ilimin ƙasa ta nuna cewa ruwan da ya kafa wannan fasalin ya gudana a kan Channeled Scablands, yana fashewa daga tafkin glacial Missoula a lokacin wani taron da aka sani da Ambaliyar Missoula kuma ya shiga cikin Kogin Columbia.&nbsp;

### Shaida a cikin yanayin karst
A kan Kogin Upper Cumberland, Tennessee, akwai jerin koguna da aka watsar da su wanda har yanzu yana riƙe da kogin da aka ajiye. Wadannan koguna sun kasance batun ƙoƙari na auna yawan ƙaurawar wuka tare da kogi, da kuma kimanta fitarwa da kogi a tsawon lokaci. A cikin yanayin karst, kogin da ke sauka a matakin yana tasiri fiye da tashinsa kawai; saboda babu ruwa da ke gudana a wani matakin, koguna da teburin ruwa za su sauka a cikin gida zuwa sabon matakin.

### Shaidar raguwar matakin tushe mai girma
Ana iya ganin manyan magudanar ruwa a cikin tekuna a duk faɗin duniya sun ci gaba a kan ƙasa wanda aka taɓa fallasawa, ko saboda raguwar tectonic, hauhawar matakin teku, ko wasu dalilai. Hotunan Bathymetric suna samuwa ga yawancin gabar yammacin Amurka, kuma musamman ƙasa ta teku kawai kusa da koguna a Arewa maso Yammacin Pacific suna nuna irin waɗannan fasalulluka na karkashin ruwa.

A wasu wurare har yanzu akwai wuraren da aka adana a cikin waɗannan tashoshin kogi da kwari da aka nutsar. Wani binciken da aka gudanar a cikin Yankin Bahar Rum  ya mayar da hankali kan irin waɗannan fasalulluka. A nan, an yi yanka ne ta hanyar rufe Bahar Rum a ƙarshen Miocene. Wannan rashin kwatsam na ruwan teku ya ba da damar kwandon ya ragu a cikin girma kuma ya karu da gishiri, kuma sakamakon raguwar matakin ƙasa da yawa daga cikin koguna waɗanda ke gudana har yanzu a yau zuwa cikin Bahar Rum sun fara yanka.

## Motsi
Kamar yadda aka lura da manyan magudanan ruwa da yawa, knickpoints suna ƙaura zuwa sama saboda rushewar dutse  suna barin tashoshi masu zurfi da wuraren ambaliyar da aka watsar, wanda ya zama terraces. Ana iya nuna sauƙin koma baya na Knickpoint a wasu wuraren da suka shafi amsawar isostatic ta bayan dusar ƙanƙara da raguwar matakin teku kamar a Scotland. A wasu yankuna, kwanan wata na dutsen da aka fallasa ya fi dacewa da sashi na sararin samaniya da juriya na knickzone a kusan wuri ɗaya.

Kogin, bayan ya sami ko ya rasa makamashi mai yuwuwa tare da canjin gangaren, zai ci gaba da aiki da maɓallan cuta daga tsarinsa ta hanyar ko dai lalacewa (a cikin yanayin magudanan ruwa; ya sami makamashi) ko kuma ajiyewa (a cikin tabkuna; ya rasa makamancin makamashi).

Yawan ƙaura na knickpoint, a cikin yanayin magudanan ruwa, gabaɗaya suna tsakanin 1mm da 10 cm a kowace shekara, tare da wasu ƙididdiga na musamman.&nbsp;

### Tsarin lissafi
Ana yin yaduwar Knickpoint yawanci tare da dokar wutar lantarki ta rabin kwarewar inda ake amfani da girman kwandon ruwa a matsayin wakili don fitarwa, wanda hakan ke da kyakkyawar alaƙa da ba ta layi ba ga yawan ƙaurawar knickpoint. Dukkanin hanyoyin bincike  da na lambobi  an ba da shawarar warware dokar ikon rafi.

## Cirewa ta atomatik a cikin GIS
Knickpoints da knickzones za a iya cire su ta atomatik daga Digital Elevation Models a cikin software na Tsarin Bayanai na Yanayi (watau ArcGIS). Matsalar da ke tattare da mafi yawan hanyoyin da ke akwai ita ce sau da yawa suna da ra'ayi kuma suna buƙatar sarrafa bayanai masu cin lokaci. Maganin waɗannan matsalolin kayan aiki ne da aka tsara don ArcGIS, wanda ake kira Knickzone Extraction Tool (KET) wanda ke sarrafa tsarin cirewa.

## Manazarta