Yankewar kogin

Yankewar kogin shine narkewar lalacewa da kogi ko rafi ya haifar wanda ke nesa da matakin tushe. Yankewar kogi ya zama ruwan dare bayan tasowa na tectonic na wuri mai faɗi. Yankewar koguna da yawa yana haifar da shimfidar wuri, alal misali, tudu mai laushi. Yankewar kogi shine tsari na halitta wanda kogi ke yankewa zuwa ƙasa a cikin gadonsa, yana zurfafa tashar aiki. Kodayake tsari ne na halitta, ana iya hanzarta shi da sauri ta hanyar abubuwan ɗan adam ciki har da canje-canjen amfani da ƙasa kamar girbi na katako, hakar ma'adinai, noma, da kuma gina hanya da madatsar ruwa. Adadin yankan aiki ne na basal shear-stress. Matsalar shear tana ƙaruwa ta hanyar dalilai kamar su turɓaya a cikin ruwa, wanda ke ƙara yawanta. Matsi na shear 

t 

{\displaystyle t} 

ya dace da nauyin ruwa, nauyi, da WSS:



inda t shine damuwa (N / m2), ρ shine yawan ruwa mai gudana, g shine nauyi a Duniya, D shine matsakaicin zurfin ruwa, kuma WSS shine Ruwa. Wannan yayi kama da damuwa ta basal shear da aka saba amfani da ita a cikin glaciology. Ƙara a cikin gangara, zurfi, ko yawan ruwa yana ƙara yiwuwar ruwa don haifar da rushewa.

 Dalilan da suka haifar 
PKashe katako na gargajiya a gabar tekun Yammacin Amurka ya haɗa da ayyuka da yawa waɗanda suka kara yawan yankan kogi. Cire katako da kuma gine-ginen da ke tattare da shi suna sauƙaƙa runoff kuma ta haka ne ya kara lalacewa da isar da turɓaya zuwa rafi. Ƙara a cikin laka yana ƙara ƙarfin rafin ruwa, yana ƙara ikon rafin don yin aikin geomorphic a kan gado da bankunan. Wannan yana haifar da tsaftace kayan gado, yana fallasa gadon tashar dutse zuwa rushewa kuma ta haka ne saurin saurin tashar. Abubuwan da aka wanke a gado sun ƙunshi mafi kyawun lakabi kamar silts, yashi, da dutse. Cire waɗannan yana cire mahimman wuraren zama na ruwa ga nau'in salmonid da sauran kwayoyin ruwa. A yankuna da yawa na noma, an daidaita koguna kuma an rufe su don kula da ambaliyar ruwa da kuma shuka amfanin gona a cikin ambaliyar. Yawancin lokaci, ana ba da izinin ambaliyar ruwa ta bazu a fadin ambaliyar, tana ba da izini ga zubar da turɓaya da rage saurin ruwa, yana rage yiwuwar lalacewar ruwa. Gudanarwa yana mai da hankali ga ambaliyar ruwa a kan tashar aiki, yana ƙara lalacewa. Yankewar kogi saboda aikin gona an rubuta shi sosai a duk yankunan noma na duniya, kamar Central Valley of California.

Har ila yau, an rubuta ma'adinai masu kyau a matsayin dalilin yankan kogi. Abubuwan da suka dace a kan kogin suna rage lalacewa,  cire wannan makamai na dutse, duwatsu, da dai sauransu yana fallasa gadon tashar ga ƙarfin lalacewa na ruwa. "A kan Kogin Rasha kusa da Healdsburg, California, ma'adinai na ma'adanai a cikin shekarun 1950 da 1960 sun haifar da yankan tashar da ya wuce 3-6 m a kan tsawon kilomita 11 na kogi. "Kondolf, G.M.; Piégay, H.; Landon, N. (2002). "Channel response to increased and decreased bedload supply from land use change: Contrasts between two catchments". Geomorphology. 45 (1–2): 35–51. Bibcode:2002Geomo..45...35K. doi:10.1016/S0169-555X(01)00188-X. 

Tectonics suna taka muhimmiyar rawa wajen tsara shimfidar wurare da koguna, kuma tasowa na tectonic da yankan kogi suna tafiya hannu da hannu. A lokacin ilimin ƙasa, yayin da duwatsu suka tashi sama, ruwa yana lalata zurfin gorges da tashoshi, yana rarraba wuri mai faɗi. A wasu lokuta, kamar tsaunukan Sierra Nevada na California, an nuna cewa an yi amfani da kilomita 1 a cikin shekaru miliyan 5 da suka gabata. "Rugujewar kogin tana ɗaya daga cikin manyan wakilai na juyin halitta. A waje da yankuna masu dusar ƙanƙara, koguna suna da alhakin ƙera ƙasa mai tsawo a cikin hanyoyin sadarwar kwarin arborescent da ƙirƙirar taimako wanda ke fitar da hanyoyin sufuri masu nauyi kamar shimfidawa". Koguna da rafi da ke ƙetare iyakokin tectonic suna ƙarƙashin babban canjin geomorphic. Lokacin da wani yanki a cikin hanyar kogi ya tashi, kogin dole ne ya karkatar da shi, ko kuma a hankali ya shiga cikin yankin da aka ɗaga, ya haifar da gorge ko canyon. 

 Tasirin 

 Raguwar matakin ruwa 
As a channel bed drops, the water in the surrounding aquifer runs into the stream, lowering the water table. This modifies the flow regime of a stream, and can lead to a large reduction in summer flows. Prolonged incision can lower the water table to the point where the roots of the riparian vegetation can no longer access it for water, causing the death of the riparian forest and thus a loss of soil stability, contributing to increased sedimentation.[<span title="This claim needs references to reliable sources. (December 2020)">citation needed</span>] Riparian forests are some of the most productive and diverse ecosystems on the planet and are for this reason the focus of many restoration projects throughout the United States.

 Canji a cikin siffar tudun 
A ƙananan ƙarancin lalacewa, ƙarancin rafi na iya yin gangara mai laushi don lalatawa don ƙirƙirar siffofi masu laushi. Tuddan da ke kewaye da rafi na iya nuna hanzarin hawan gashi. Wannan shi ne saboda hanzarin yankan na iya haifar da hanzarin lalacewa a kan gangaren da ke kusa da su wanda ke haifar da gangaren da suka fi tsayi waɗanda ke cikin daidaito tare da yawan lalacewa.

 Bayani 
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