گزارش فني: بررسي كارايي مدل EPM از طريق رسوب سنجي مخازن بندهاي كوچك

Technical Note: Evaluation of EPM empirical model using sediment survey of small reservoirs in Fars Province

ﻣﺴﺄﻟﻪ ﻓﺮﺳﺎﯾﺶ و رﺳﻮب ﺣﺎﺻﻞ از آن، از ﻣﻬﻤﺘﺮﯾﻦ ﻣﺴﺎﺋﻞ آﺑﺨﯿﺰداري اﺳﺖ. در اﯾﻦ راﺳﺘﺎ، ﺑﺮآورد رﺳﻮب و اوﻟﻮﯾﺖ ﺑﻨﺪي ﺣﻮزه ﻫﺎي آﺑﺨﯿﺰ از ﻟﺤﺎظ ﻓﺮﺳﺎﯾﺶ آﺑﯽ از اﻫﺪاف ﻣﻬﻢ آﺑﺨﯿﺰداري اﺳﺖ. ﯾﮑﯽ از راه ﻫﺎي ﺑﺮآورد ﻓﺮﺳﺎﯾﺶ ﺧﺎك و ﺗﻮﻟﯿﺪ رﺳﻮب، اﺳﺘﻔﺎده از ﻣﺪلﻫﺎي ﺗﺠﺮﺑﯽ اﺳﺖ. ﻫﺪف از اﺟﺮاي اﯾﻦ ﭘﮋوﻫﺶ، ﺑﺮرﺳﯽ ﮐﺎراﯾﯽ ﻣﺪل EPM در اﺳﺘﺎن ﻓﺎرس اﺳﺖ. در اﯾﻦ ﻣﺪل، ﭘﺎراﻣﺘﺮﻫﺎﯾﯽ ﻣﺎﻧﻨﺪ ﺿﺮﯾﺐ ﺷﺪت ﻓﺮﺳﺎﯾﺶ، ﻓﺮﺳﺎﯾﺶ وﯾﮋه و ﻣﯿﺰان رﺳﻮبدﻫﯽ وﯾﮋه ﻣﻮرد ﺑﺮرﺳﯽ ﻗﺮار ﮔﺮﻓﺘﻨﺪ. ﺑﺮاي اﯾﻦ ﮐﺎر، ﭘﻨﺞ ﺣﻮزه آﺑﺨﯿﺰ ﮐﻮﭼﮏ در اﺳﺘﺎن ﻓﺎرس اﻧﺘﺨﺎب ﺷﺪﻧﺪ. در ﺧﺮوﺟﯽ اﯾﻦ ﺣﻮﺿﻪ ﻫﺎ، ﺑﻨﺪﻫﺎي ﺧﺎﮐﯽ و ﺳﻨﮕﯽ -ﻣﻼﺗﯽ ﺑﻨﺎ ﺷﺪه ﮐﻪ ﺗﺎ ﮐﻨﻮن ﺳﺮرﯾﺰ ﻧﺪاﺷﺘﻪ و ﺳﻦ ﺑﯿﺸﺘﺮ آن ﻫﺎ ﻧﺰدﯾﮏ ﺑﻪ 10 ﺳﺎل اﺳﺖ. ﺑﺎ اﺳﺘﻔﺎده از ﻧﻘﺸﻪ ﺑﺮداري دﻗﯿﻖ، ﻣﻘﺪار رﺳﻮﺑﺎت ﺗﻪ ﻧﺸﯿﻦﺷﺪه در ﻣﺨﺎزن آن ﻫﺎ ﺑﻪدﺳﺖ آﻣﺪ. وزن ﻣﺨﺼﻮص ﻇﺎﻫﺮي رﺳﻮﺑﺎت ﺑﺎ ﻋﻤﻠﯿﺎت ﺻﺤﺮاﯾﯽ، ﺗﻌﯿﯿﻦ و ﺣﺠﻢ رﺳﻮﺑﺎت ﺑﺎ در ﻧﻈﺮ ﮔﺮﻓﺘﻦ ﺳﺎل ﻫﺎي رﺳﻮب ﮔﯿﺮي ﺑﻪ وزن ﺗﺒﺪﯾﻞ ﺷﺪ. ﺑﺎ اﺳﺘﻔﺎده از ﻣﺪل EPM، ﻣﻘﺪار ﺣﺠﻢ و وزن رﺳﻮب ﺗﻮﻟﯿﺪي ﺣﻮﺿﻪ ﻫﺎ ﺗﻌﯿﯿﻦ ﺷﺪﻧﺪ. ﮐﻤﯿﻨﻪ و ﺑﯿﺸﯿﻨﻪ اﻧﺪازه ﮔﯿﺮي رﺳﻮب ﺑﻨﺪﻫﺎ ﺑﯿﻦ 0/89 ﺗﺎ 2/62 ﺗﻦ در ﻫﮑﺘﺎر در ﺳﺎل ﺗﻐﯿﯿﺮ داﺷﺘﻪ، وﻟﯽ ﻣﯿﺰان رﺳﻮب ﺑﺮآوردي ﻣﺪل ﺑﯿﻦ 3/3 ﺗﺎ ﺷﺶ ﺗﻦ در ﻫﮑﺘﺎر در ﺳﺎل ﻣﺘﻐﯿﺮ ﺑﻮده اﺳﺖ. ﻧﺘﺎﯾﺞ درﺻﺪ ﺧﻄﺎي ﻧﺴﺒﯽ ﺑﺮآوردﻫﺎي ﻣﺪل EPM ﻧﺸﺎن از ﺑﯿﺶﺑﺮآوردي در ﺗﻤﺎم ﺣﻮﺿﻪ ﻫﺎ دارد )ﮐﻤﯿﻨﻪ 121/5 و ﺑﯿﺸﯿﻨﻪ 447/2 درﺻﺪ(. ﻣﯿﺎﻧﮕﯿﻦ ﻧﺴﺒﯽ ﻣﺮﺑﻌﺎت ﺧﻄﺎي ﻣﺪل )RRMSE( ﺑﺮاﺑﺮ 2/39 ﻣﺤﺎﺳﺒﻪ ﺷﺪ ﮐﻪ ﻧﺸﺎن دﻫﻨﺪه ﺧﻄﺎي زﯾﺎدي اﺳﺖ. ﻧﺘﺎﯾﺞ ﺗﺤﻠﯿﻞ آﻣﺎري ﻣﻘﺎﯾﺴﻪ ﻣﻘﺎدﯾﺮ رﺳﻮبدﻫﯽ واﻗﻌﯽ ﺣﻮزهﻫﺎي آﺑﺨﯿﺰ ﺑﺎ ﻣﻘﺎدﯾﺮ ﺑﺮآوردﺷﺪه ﺑﻪ وﺳﯿﻠﻪ ﻣﺪل، ﺑﺎ اﺳﺘﻔﺎده از روش آﻣﺎري t زوﺟﯽ، ﻧﺸﺎن ﻣﯽ دﻫﺪ ﮐﻪ اﺧﺘﻼف ﻣﻌﻨﯽ داري )t=8/728 و 0/001=sig( ﺑﯿﻦ اﯾﻦ ﻣﻘﺎدﯾﺮ وﺟﻮد دارد. ﺑﺮ اﺳﺎس ﻧﺘﺎﯾﺞ ﺑﻪدﺳﺖ آﻣﺪه از اﯾﻦ ﭘﮋوﻫﺶ، ﻣﺪل EPM ﺑﺮاي ﻣﻨﺎﻃﻖ ﻣﻮرد ﭘﮋوﻫﺶ ﭘﺬﯾﺮﻓﺘﻪ ﺷﺪه ﻧﯿﺴﺖ.

Erosion and sediment resulting from it, is one of the most important factors in watershed management. The estimation of sediment yield and prioritization of watersheds in terms of water erosion is the main objectives of watershed management. One of the ways to estimate soil erosion and sediment yield is to use empirical models. The aim of this research is to evaluate the efficiency of the EPM Model in Fars Province. To examine this, five small watersheds were selected in Fars Province. Five basins in which the earth dams and check dams were built were selected. There is no overflow from these dams in rainfall events and the most of them was made near to 10 years. The amount of sediment deposited in upstream of the reservoirs was calculated by means of precision mapping. Deposit bulk density was determined in the field to convert the volume into the weight. In parallel, the sediment yield of the basins was determined by EPM Model. Results showed that the minimum and maximum sediment yield measurements varied from 0.89 to 2.62 tonh-1y-1, but the estimated sediment was between 3.3 to 6 tonh-1y-1. The results of the relative error of estimation of EPM Model in each of the studied basins showed an over estimation in all basins (minimum 121.5 and maximum 447.2 percent). The Relative Root Mean Square Error (RRMSE) of the model was calculated as 2.39, which indicates a too much error of the model. Statistical analysis results comparison of actual sediment yields of watersheds with estimated values by model, using paired t-test, shows that there is a significant difference between these values (t=8.728 and sig.=0.001). According to the presented findings, the results of this model estimation for the investigated areas are not accepted.