ارزيابي اثرات توسعه شهري بر رواناب با استفاده از مدل SWMM (مطالعه موردي: استان قم)

Evaluation of Urban Development Impacts on Runoff Using SWMM Model (Case Study: Qom Province)

زﻣﯿﻨﻪ و ﻫﺪف: در ﯾﮏ ﺣﻮزه آﺑﺨﯿﺰ ﻃﺒﯿﻌﯽ ﺑﯿﺸﺘﺮ ﺳﻄﺢ زﻣﯿﻦ ﻧﻔﻮذﭘﺬﯾﺮ و ﺑﻪ وﺳﯿﻠﻪ ﭘﻮﺷﺶ ﮔﯿﺎﻫﯽ ﭘﻮﺷﯿﺪه ﺷﺪه اﺳﺖ، ﺑﻪ ﻫﻤﯿﻦ ﺟﻬﺖ ﻣﻘﺪار زﯾﺎدي از ﺑﺎرش از راه ﮔﯿﺮش ﮔﯿﺎﻫﯽ، ﻧﻔﻮذ در ﺧﺎك و ﺗﺒﺨﯿﺮ و ﺗﻌﺮق از دﺳﺖ ﻣﯽرود. اﻣﺎ در ﯾﮏ ﺣﻮزه آﺑﺨﯿﺰ ﺷﻬﺮي ﺑﻪ دﻟﯿﻞ ﺷﻬﺮ-ﺳﺎزي، ﺳﻄﺢ ﻧﻔﻮذﻧﺎﭘﺬﯾﺮ ﺣﻮﺿﻪ اﻓﺰاﯾﺶ ﻣﯽﯾﺎﺑﺪ ﮐﻪ اﻓﺰاﯾﺶ ﺣﺠﻢ رواﻧﺎب و دﺑﯽ اوج، ﻓﺮﺳﺎﯾﺶ ﮐﻒ و ﮐﻨﺎرهﻫﺎي ﮐﺎﻧﺎلﻫﺎي ﭘﺎﯾﯿﻦ دﺳﺖ و ﮐﺎﻫﺶ ﺳﻄﺢ آب زﯾﺮزﻣﯿﻨﯽ و ﺗﺨﺮﯾﺐ ﮐﯿﻔﯿﺖ آب را ﺑﻪ دﻧﺒﺎل دارد. ﻫﺪف از اﯾﻦ ﺗﺤﻘﯿﻖ، ﮐﺎرﺑﺮد ﺷﺒﯿﻪﺳﺎزي SWMM ﺑﺮاي ﺑﺮآورد ارﺗﻔﺎع رواﻧﺎب و ﻫﻤﭽﻨﯿﻦ ﻫﯿﺪروﮔﺮاف رواﻧﺎب و ﺑﺮرﺳﯽ اﺛﺮات ﺗﻐﯿﯿﺮات ﭘﻮﺷﺶ اراﺿﯽ و ﻣﻮﻗﻌﯿﺖ ﭘﻮﺷﺰش اراﺿﯽ و اﺑﺰارﻫﺎي ﺗﻮﺳﻌﻪ ﮐﻢ اﺛﺮ ﺑﺮ ﭘﺎﺳﺦ ﻫﯿﺪروﻟﻮژﯾﮑﯽ ﺣﻮزه آﺑﺨﯿﺰ ﺷﻬﺮي ﺑﺎ اﺳﺘﻔﺎده از ﻣﺪل ﻣﻮرد ﻧﻈﺮ ﻣﯽﺑﺎﺷﺪ. روش ﺑﺮرﺳﯽ: ﺑﺮاي اﻧﺠﺎم اﯾﻦ ﺗﺤﻘﯿﻖ اﺟﺮاي ﻣﺪل SWMM در ﯾﮑﯽ از ﻣﻨﺎﻃﻖ ﺷﻬﺮي ﺷﻬﺮ ﻗﻢ ﻣﺪ ﻧﻈﺮ ﻗﺮار ﮔﺮﻓﺖ. ﺣﻮﺿﻪ ﻣﻮرد ﻣﻄﺎﻟﻌﻪ ﺑﺎ وﺳﻌﺘﯽ ﻣﻌﺎدل 256 ﻫﮑﺘﺎر در ﺑﺨﺶ ﺷﻤﺎل ﻏﺮﺑﯽ ﻗﻢ واﻗﻊ ﺷﺪه اﺳﺖ. ﯾﺎﻓﺘﻪﻫﺎ: در اﯾﻦ ﺗﺤﻘﯿﻖ ﻧﺘﯿﺠﻪﮔﯿﺮي ﺷﺪ ﮐﻪ در دو زﯾﺮﺣﻮﺿﻪ دو و ﺷﺶ اﻓﺰاﯾﺶ 70 و 40 درﺻﺪي ﺳﻄﻮح ﻧﻔﻮذﻧﺎﭘﺬﯾﺮ ﻣﻮﺟﺐ اﻓﺰاﯾﺶ 30 درﺻﺪ در ﻣﻘﺪار رواﻧﺎب ﻣﯽﺷﻮد. ﻫﻤﭽﻨﯿﻦ اﻓﺰاﯾﺶ 10 درﺻﺪ ﺳﻄﺢ ﻧﻔﻮذﻧﺎﭘﺬﯾﺮ در ﺣﻮﺿﻪ آﺑﺨﯿﺰ ﺑﺎﻻدﺳﺖ و ﭘﺎﯾﯿﻦ دﺳﺖ ﺣﻮﺿﻪ ﺑﻪ ﺗﺮﺗﯿﺐ ﻣﻮﺟﺐ اﻓﺰاﯾﺶ 6/51 و 6/87 درﺻﺪ اﻓﺰاﯾﺶ در دﺑﯽ اوج ﻣﯽﺷﻮد. ﮐﻪ ﺑﯿﺎﻧﮕﺮ آن اﺳﺖ ﮐﻪ ﻣﻮﻗﻌﯿﺖ ﻣﮑﺎﻧﯽ ﺳﻄﺢ ﻧﻔﻮذﻧﺎﭘﺬﯾﺮ ﺗﺄﺛﯿﺮ اﻧﺪﮐﯽ ﺑﺮ ﻣﯿﺰان رواﻧﺎب دارد. اﺳﺘﻔﺎده از اﺑﺰار ذﺧﯿﺮهاي ﻧﯿﺰ ﺗﺄﺛﯿﺮ ﭼﺸﻤﮕﯿﺮي ﺑﺮ ﮐﺎﻫﺶ ﻣﯿﺰان رواﻧﺎب ﺷﻬﺮي داﺷﺘﻪ اﺳﺖ. ﺑﺤﺚ و ﻧﺘﯿﺠﻪ ﮔﯿﺮي: ﻧﺘﺎﯾﺞ ﺣﺎﺻﻞ از ﻣﺪل SWMM در ﺑﺮآورد رواﻧﺎب ﺷﻬﺮي ﺑﯿﺎن ﻣﯽدارد ﮐﻪ ﺑﻪ ﻣﻨﻈﻮر ﻣﺪﯾﺮﯾﺖ ﺑﻬﯿﻨﻪ رواﻧﺎب در ﻣﻨﺎﻃﻖ ﺧﺸﮏ ﺑﺎﯾﺴﺘﯽ اﺛﺮات ﻣﯿﺰان و ﻣﻮﻗﻌﯿﺖ ﮐﺎرﺑﺮي اراﺿﯽ ﺑﺮ ﻣﯿﺰان رواﻧﺎب ﺷﻬﺮي و ﻫﻤﭽﻨﯿﻦ اﺳﺘﻔﺎده از اﺑﺰارﻫﺎي ذﺧﯿﺮه ﺑﺎران در اﯾﻦ ﻣﻨﺎﻃﻖ ﻣﺪﻧﻈﺮﻗﺮارﮔﯿﺮد.

Background and Objective: In a natural watershed, most of the surface is impervious and covered with vegetation, so a large amount of precipitation is lost through plant interception, infiltration into soil and evapotranspiration. However, in an urban watershed due to urbanization, impervious surface of the watershed increases, which tends to increase the volume of runoff and peak discharge, the erosion of the bed and the edges in the downward of canals, and decrease in water level as well as degradation of water quality. The purpose of this research is to apply SWMM simulation for estimating runoff and runoff hydrograph and the effects of land cover changes and low impact development tools on hydrologic response of urban watersheds. Method: In this research, implementation of SWMM model in one of the urban areas of Qom was considered. The study area is 256 hectares in northwestern part of Qom. Findings: In this study, it was concluded that in sub watershed of 2 and 6, the increase of 70% and 40% in impervious surfaces resulted in 30% increase in runoff volume. Also, 10% increase in impervious area of upstream and downstream of watershed tends to 6/51% and 6/87% increase in peak discharge volume, respectively. The use of storage devices has also had a significant impact on reducing urban runoff. Discussion and Conclusion: The results of SWMM model in urban runoff estimation indicate that in order to properly manage runoff in arid areas, the status and location effects of land use on urban runoff rate as well as the use of rain storage tools in these areas should be considered.