تغييرات مكاني-زماني فرسايش خاك در حوزه آبخيز معرف خامسان با استفاده از مدل RUSLE

Spatio-temporal variation of soil erosion in Khamsan representative watershed using RUSLE

ﭘﻮﯾﺎﯾﯽ ﻋﻮاﻣﻞ ﻓﺮﺳﺎﯾﻨﺪﮔﯽ ﺑﺎران )R(، ﻣﺪﯾﺮﯾﺖ زراﻋﯽ )C( و ﻓﺮﺳﺎﯾﺶ ﭘﺬﯾﺮي ﺧﺎك )K( در ﻣﻘﺎﯾﺴﻪ ﺑﺎ دﯾﮕﺮ ﻋﻮاﻣﻞ ﺗﻮﭘﻮﮔﺮاﻓﯽ، LS و ﻣﺪﯾﺮﯾﺖ اراﺿﯽ، P(، ﻣﻬﻤﺘﺮﯾﻦ ﻧﮑﺘﻪ در ﺑﺮآورد ﺻﺤﯿﺢ ﻓﺮﺳﺎﯾﺶ ﺧﺎك در ﭘﺎﯾﻪ ﻫﺎي زﻣﺎﻧﯽ ﻣﺨﺘﻠﻒ اﺳﺖ. ﺑﺮآوردﻫﺎي ﻣﮑﺎﻧﯽ-زﻣﺎﻧﯽ ﻓﺮﺳﺎﯾﺶ ﺧﺎك در ﺣﻮزه ﻫﺎي آﺑﺨﯿﺰ ﻣﻌﺮف-زوﺟﯽ ﺑﻪدﻟﯿﻞ ﮐﺎرﮐﺮدﻫﺎي آﻣﻮزﺷﯽ آن ﻫﺎ و ﻧﯿﺰ اﻣﮑﺎن ﺗﻌﻤﯿﻢ ﻧﺘﺎﯾﺞ ﺑﺮاي ﻣﻨﺎﻃﻖ ﺑﺰرگ ﺗﺮي از ﮐﺸﻮر از اﻫﻤﯿﺖ وﯾﮋه اي ﺑﺮﺧﻮردار اﺳﺖ. ﺑﻨﺎﺑﺮاﯾﻦ، در ﭘﮋوﻫﺶ ﺣﺎﺿﺮ ﺿﻤﻦ ﺑﺮرﺳﯽ ﭘﻮﯾﺎﯾﯽ ﻋﻮاﻣﻞ C ،R و K در ﺣﻮزه آﺑﺨﯿﺰ ﻣﻌﺮف-زوﺟﯽ ﺧﺎﻣﺴﺎن، ﻧﻘﺸﻪ ﺗﻮزﯾﻌﯽ ﻓﺮﺳﺎﯾﺶ ﺧﺎك در ﻣﻘﯿﺎس ﻫﺎي زﻣﺎﻧﯽ ﻓﺼﻠﯽ و ﺳﺎﻻﻧﻪ ﺑﺎ اﺳﺘﻔﺎده از ﻣﺪل RUSLE ﺑﺮاي دو ﺳﺎل آﺑﯽ 1394-95 و 1396-97 ﺗﻬﯿﻪ ﺷﺪ. ﻧﺘﺎﯾﺞ ﻧﺸﺎن داد ﮐﻪ ﻓﺮﺳﺎﯾﺶ ﺧﺎك در ﻓﺼﻞ زﻣﺴﺘﺎن ﺑﺎ ﻣﻘﺎدﯾﺮ 3/94 و 4/59 ﺗﻦ در ﻫﮑﺘﺎر ﺑﻪﺗﺮﺗﯿﺐ ﺣﺪود 49 و 74 درﺻﺪ از ﮐﻞ ﻓﺮﺳﺎﯾﺶ ﺳﺎل را ﺑﻪ ﺧﻮد اﺧﺘﺼﺎص داد. در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﺷﺮاﯾﻂ ذوب در ﻣﺤﺎﺳﺒﻪ ﻋﺎﻣﻞ K ﺑﺮاي ﻓﺼﻞ زﻣﺴﺘﺎن ﻫﻤﺮاه ﺑﺎ ﻓﻘﺪان ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ در اﯾﻦ ﻓﺼﻞ ﻣﻨﺠﺮ ﺑﻪ ﺑﺮآورد ﺑﯿﺸﺘﺮ ﻓﺮﺳﺎﯾﺶ ﺧﺎك ﻧﺴﺒﺖ ﺑﻪ دﯾﮕﺮ ﻓﺼﻮل ﺷﺪ. اﯾﻦ ﻧﺘﺎﯾﺞ ﺑﺎ داده ﻫﺎي ﻫﺪررﻓﺖ ﺧﺎك ﮐﺮت ﻫﺎ در رﮔﺒﺎرﻫﺎي ﺛﺒﺖ ﺷﺪه در ﻓﺼﻮل ﻣﺨﺘﻠﻒ و ﻫﻤﭽﻨﯿﻦ، ﻏﻠﻈﺖ ﺑﯿﺸﺘﺮ رﺳﻮﺑﺎت ﻣﻌﻠﻖ در رودﺧﺎﻧﻪ ﻫﺎ ﺑﻪ وﯾﮋه در اﺳﻔﻨﺪ ﻣﺎه ﺗﻄﺎﺑﻖ دارد. در ﺳﺎل آﺑﯽ 1394-95 ﺗﻮزﯾﻊ ﺑﺎرﻧﺪﮔﯽ ﻫﺎ در ﻓﺼﻞ ﭘﺎﯾﯿﺰ ﺑﻪ ﻣﺮاﺗﺐ ﺑﯿﺸﺘﺮ از ﻓﺼﻞ ﺑﻬﺎر ﺑﻮد و ﻟﺬا، ﻓﺮﺳﺎﯾﺶ ﺧﺎك ﻓﺼﻞ ﭘﺎﯾﯿﺰ ﺣﺪود 33 درﺻﺪ از ﮐﻞ ﻓﺮﺳﺎﯾﺶ ﺳﺎل را ﺑﻪ ﺧﻮد اﺧﺘﺼﺎص داد. در ﺳﺎل آﺑﯽ 97- 1396 اﮔﺮﭼﻪ ﻣﺘﻮﺳﻂ ﻓﺮﺳﺎﯾﺶ ﺧﺎك ﺳﺎﻻﻧﻪ ﮐﻤﺘﺮ ﺑﻮد، اﻣﺎ ﺑﻪدﻟﯿﻞ ﺗﻮزﯾﻊ ﺑﯿﺸﺘﺮ ﺑﺎرﻧﺪﮔﯽ ﻫﺎي ﻓﺮﺳﺎﯾﻨﺪه در ﻓﺼﻞ زﻣﺴﺘﺎن و ﻫﻢ زﻣﺎن ﺑﺎ ﻓﻘﺪان ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ روي ﺳﻄﺢ ﺧﺎك و ﻧﯿﺰ ذوب ﺧﺎك، ﺷﺪت ﻓﺮﺳﺎﯾﺶ ﻓﺼﻞ زﻣﺴﺘﺎن ﺑﺴﯿﺎر ﺑﺎﻻ ﺑﻮد.

The dynamics of rainfal erosivity (R), crop management (C) and soil erodibility (K) factors compared to the others (topography-LS and land management-P) is the most important note for the correct estimate of soil erosion at different time bases. Spatio-temporal estimates of soil erosion in the representative paired watersheds are of particular importance due to their educational functions as well as the possibility of generalizing the results to larger areas of the country. Therefore, in the present study, while examining the dynamics of R, C and K factors in the Khamsan representative paired watershed, the distribution map of soil erosion in seasonal and annual time scales were prepared using RUSLE model for two water years of 2015-2016 and 2017-2018. The results showed that soil erosion in winter with values ​​of 3.94 and 4.95 t ha-1 y-1 accounted for about 49 and 74% of the total erosion of the year, respectively. Considering the melting conditions in calculating the K factor for the winter along with the lack of vegetation in this season led to a higher estimate of soil erosion than other seasons. These results are in consistent with plots soil loss data recorded in different seasons and the higher concentration of suspended sediments in the rivers especially in March. In the water year of 2015-2016, the distribution of rainfalls in the autumn was much higher than in the spring, so that soil erosion in the autumn accounted for about 33% of the total erosion of the year. In the water year of 2017-2018, although the average annual soil erosion was less, but due to more distribution of erosive rainfalls in winter at the same time with the lack of vegetation on the soil surface and the soil melting, the rate of winter erosion was very high.