عنوان مقاله [English]
River sensitivity is affected by geomorphic forms and adjusting river ability (Fryzer, 20017). Taking into account the difference adjusting capability, the behavioral sensitivity of a river can be observed over the entire river. However, there is the major various change in a behavioral regime of a river, due to episodic turbulence or disturbances events (Philips, 2009). River behavior monitoring over time shows variable behavioral sensitivity, however, it can be dynamically evaluated, so that it causes more sensitivity in some rivers and flexibility in others. This study aimed to investigate the river sensitivity of the Taleghan River emphasizing the effect of riparian vegetation.
The research tools were aril photographs and satellite images for the study period (table 1). Taleghan River was classified into 3 sections upstream, midstream, and downstream with average elevations of 1936, 1875, and 1793m, respectively, and a minimum slope of 0.009 to a maximum of 0.013. Channel stability was calculated by analysis of channel planform indices, including BI, CA, and CW. the sustainable patches with approximately sustainable area and location were determined using overlaying the aerial photographs and satellite images. The vegetation patches with an area of more than 500m were considered and the vegetation patches lower than 500m with a detachment of vegetation cover. The riparian vegetation degradation was observed using field observation over the study period.
Results & discussion
Based on the findings, the SI index was approximately similar for the entire river and it is in the high level of sensitivity; however, the SI index was increased over 1370-13855. So, the distribution of the change over 2006-2021 is lower than 1991-2006, although the change level in 2021 is more and the change distribution is lower. It means that the change processes in all reaches are approximately the same. The relationship between the CW and CA with the BI index was explained using an X-Y plot (figure 4). The findings showed a significant correlation between the BI and CA with CA. River geomorphic sensitivity and the change level decreased and increased, respectively in 2021 than the past period (table 4). 82 sustainable vegetation patches were detected on the left and right banks of the Taleghan River during the study period. The area of the vegetation patches was 19.51%, 32.92%, 31.70%, 13.41%, and 2.46% in sub-reaches 1, 2, 3, 4, and 5, respectively. The degraded patches were in the sub-reach 1 and most of them were located near the river banks because of the establishment of vegetation patches near the river banks (fluvial traces), river undercutting due to the high hydraulic tension, and decreased bed weight and erosion by water flow. In other sub reaches changes in the turbulence intensity profile caused the distance of maximum levels from river banks.
In this study, BI, CW, CA, and SI indices in the 1st sub-reach with sinusoidal-straight planform during the studied period are lower compared to other intervals, and the amount of sedimentation is higher compared to erosion. The geomorphic sensitivity has decreased significantly in 2021 compared to the previous period and the area of the sustainable patches with a length of 3603.18 meters was 27.89645 square meters. Therefore, the least changes in geomorphology were observed in sub-reach 1, while the area of the sustainable patches in this sub-reach is more compared to other sub-reaches. It was observed that the vegetation patches were established in the sub reach 1 and part of the sub reach 2 on the immediate side of the river, and it has played a significant role in reducing erosion, adhesion of soil particles, and preventing the separation of soil particles, and hence increasing cohesion against erosion. However, the level of vegetation degradation in sub-reach 1 is significant due to the increase of hydraulic stress gradient compared to other sub-reaches. The ascending order of geomorphic sensitivity was observed in sub-reaches 1, 5, 4, 2, and 3, respectively in 2021. Whereas, the ascending order of geomorphic sensitivity was observed in sub-reaches 4, 1, 2, 5, and 3, respectively in 2006. Meanwhile, sub-reach 1 had a balanced trend and on the other hand, geomorphic sensitivity in sub-reach 3 was more than in other sub-reaches in the studied period (Table 4). Our observations have shown that in the vegetation patches, a combination of woody vegetation can be introduced as ecosystem engineers; because they have caused the increase of sedimentation and the creation of sedimentary tails, and the formation of landforms. The engineering effect of vegetation typologies along the Taleghan River has mainly occurred in places with a suitable physical location for sedimentation related to flow characteristics. River engineer species can develop different response characteristics to hydrogeomorphic constraints, therefore making possible their establishment in an unsustainable and disturbed geomorphic environment.
"Kama ilivyoelezwa hapo juu, ""Uwezo wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto wa Mto.""" Kwa kuzingatia tofauti ya kurekebisha uwezo, tabia ya unyeti wa mto inaweza kuchunguzwa juu ya mto wote. Hata hivyo, kuna mabadiliko makubwa katika tabia ya mto, kutokana na matukio ya msukosuko au usumbufu (Philipps, 2009). Ufuatiliaji wa tabia ya mto kwa muda unaonyesha unyeti wa tabia tofauti, hata hivyo, inaweza kutathminiwa kwa nguvu, ili kusababisha unyeti zaidi katika mito fulani na kubadilika kwa wengine. Utafiti huu ulikusudiwa kuchunguza unyeti wa mto wa Mto Taleghan ukisisitiza athari ya mimea ya kando ya mto. Vifaa vya utafiti vilikuwa picha za aril na picha za satelaiti kwa kipindi cha utafiti (meza 1). Mto Taleghan umegawanywa katika sehemu tatu: upstream, midstream, na downstream, na urefu wa wastani wa mita 3,365, 1,875, na 1,793 m, na mwinuko wa chini wa 0.009 hadi kiwango cha juu cha 0.013. Uimarishaji wa channel ulihesabiwa kwa uchambuzi wa indices ya mpango wa channel, ikiwa ni pamoja na BI, CA, na CW. Sehemu za kudumu na eneo la kudumu na eneo la kudumu zilitambuliwa kwa kutumia picha za anga na picha za satelaiti. Sehemu za mimea zenye ukubwa wa mita 500 au zaidi zilikuwa na uharibifu wa mimea. Uharibifu wa mimea ya pwani ulionekana kwa kutumia uchunguzi wa shamba katika kipindi cha utafiti. Kwa mujibu wa utafiti huo, kiwango cha SI cha mto huo kilikuwa sawa na kiwango cha juu cha unyeti, lakini kiliongezeka zaidi ya 1370-1355. Kwa hivyo, usambazaji wa mabadiliko katika kipindi cha 2006-2021 ni chini kuliko mwaka wa 1991-2006, ingawa kiwango cha mabadiliko katika 2021 ni zaidi na usambazaji wa mabadiliko ni chini. Inamaanisha kwamba michakato ya mabadiliko katika kufikia zote ni takriban sawa. Uwiano kati ya CY na CY na index ya BI ilielezwa kwa kutumia mchoro wa XY (picha 4). Matokeo ya utafiti huo yanaonyesha uhusiano mkubwa kati ya B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 na B2 Uwezo wa geomorphic wa mto na kiwango cha mabadiliko kilipungua na kuongezeka, kwa mtiririko huo, mnamo 2021 kuliko kipindi cha zamani ( Jedwali 4). Katika kipindi cha utafiti, vichaka 82 vya mimea viligunduliwa kwenye ukingo wa kushoto na kulia wa Mto Talagan. Sehemu ya mimea ilikuwa 19.51%, 32.92%, 31.70%, 13.41% na 2.46% katika sub-reaches 1, 2, 3, 4 na 5, kwa mtiririko huo. Sehemu zilizoharibiwa zilikuwa katika sehemu ya chini ya 1 na nyingi zilikuwa karibu na kingo za mto kwa sababu ya kuanzishwa kwa sehemu za mimea karibu na kingo za mto (michoro ya mto), kukata chini kwa mto kwa sababu ya mvutano wa juu wa maji, na kupungua kwa uzito wa kitanda na mmomonyoko wa maji. Katika sub hufikia mabadiliko katika profile ya nguvu ya turbulence kusababisha umbali wa viwango vya juu kutoka benki za mto. Katika utafiti huu, viashiria vya B, C, C, C, na C katika sehemu ya kwanza ya kufikia na sinusoidal-linear planform wakati wa kipindi cha utafiti ni chini ikilinganishwa na vipindi vingine, na kiasi cha sedimentation ni juu ikilinganishwa na mmomonyoko. Uwezo wa kijiografia umepungua sana mnamo 2021 ikilinganishwa na kipindi cha awali na eneo la patches endelevu na urefu wa mita 3603.18 lilikuwa mita za mraba 27.89645 Kwa hivyo, mabadiliko ya chini katika geomorphology yalionekana katika sub-reach 1, wakati eneo la patches endelevu katika sub-reach hii ni zaidi ikilinganishwa na sub-reach nyingine. "Kama ilivyoelezwa, ""mimea ya mimea imeanzishwa katika sehemu ya 1 na sehemu ya 2 ya mto, na imecheza jukumu muhimu katika kupunguza mmomonyoko, kushikamana kwa chembe za udongo na kuzuia kutenganishwa kwa chembe za udongo, na hivyo kuongeza mshikamano dhidi ya mmomonyoko.""" Hata hivyo, kiwango cha uharibifu wa mimea katika sub-reach 1 ni muhimu kutokana na ongezeko la gradient hydraulic mkazo ikilinganishwa na sub-reach nyingine. Mfuatano wa kuongezeka kwa unyeti wa kijiografia ulionekana katika sub-reaches 1, 5, 4, 2 na 3, kwa mtiririko huo mnamo 2021. Kwa mujibu wa taarifa ya Shirika la Afya la Umoja wa Mataifa, idadi ya watu walioathirika na janga hilo imepanda kwa kasi katika maeneo ya chini ya 4, 1, 2, 5 na 3 mwaka 2006. Kwa upande mwingine, sehemu ya 1 ilikuwa na mwelekeo wa usawa na kwa upande mwingine, unyeti wa kijiografia katika sehemu ya 3 ulikuwa zaidi kuliko katika sehemu nyingine za kipindi cha utafiti (tazama 4). Uchunguzi wetu umeonyesha kwamba katika vichaka vya mimea, mchanganyiko wa mimea ya mbao inaweza kuingizwa kama wahandisi wa mazingira, kwa sababu imesababisha kuongezeka kwa sedimentation na uundaji wa mikia ya sedimentary na muundo wa ardhi. Mabadiliko ya kibiashara ya aina ya mimea kando ya Mto Taleghan yametokea hasa katika maeneo yenye eneo linalofaa kwa sedimentation kuhusiana na sifa za mtiririko. Aina za mimea ya mto inaweza kuendeleza sifa tofauti za majibu kwa vikwazo vya hydrogeomorphic, hivyo kufanya iwezekanavyo kuanzisha yao katika mazingira yasiyo ya kudumu na ya geomorphic.