ارزيابي درازمدت اثرات هيدرولوژيك (L-THIA) تغيير كاربري بر رواناب سالانه در مقياس حوضه آبخيز

Long Term Hydrological Impact Assessment of Landuse Change on Surface Annual Runoff at the Catchment Scale

تغييرات رواناب به واسطه ي تغيير كاربري بسيار زياد مي باشد و اغلب مدل سازي، تنها راه بررسي احتمال بالقوه هر منطقه نسبت به سيلاب است. در اين تحقيق از مدل L-THIA براي تخمين رواناب ناشي از تغيير كاربري در چالوس و نوشهر استفاده شد. L-THIA يك ابزار مناسب براي كمك به سنجش اثرات بالقوه ي تغيير كاربري بر رواناب سطحي و آلودگي آب مي باشد. نتايج مدل سازي رواناب با استفاده از L-THIA افزايش 3/17 ميلي متر رواناب متوسط سالانه تنها در طي 14 سال را نشان مي دهد كه بيان گر افزايش 79/9 ميليون متر مكعب رواناب طي اين مدّت در منطقه مورد مطالعه است. همان طور كه از نتايج اين تحقيق بر مي آيد مدل L-THIAقابليت قابل قبولي در بيان نحوه ي اثر تغيير كاربري بر مقادير حجم و عمق رواناب، طبق سناريوهاي مختلف دارد. اين مدل با ارايه ي نقشه ي توزيع مكاني رواناب، امكان شناسايي مناطق حادثه خيز، پهنه بندي سيل و همچنين مديريت سيلاب را فراهم مي سازد. اولويّت بندي زيرحوضه هاي آبخيز براي انجام اقدامات كنترل سيلاب از ديگر قابليت هاي روش مدل سازي به كار گرفته در اين پژوهش مي باشد.

Runoff changes is high due to change in land use and often making model is the only way to evaluate the potential of each area to flood. For simulating of watershed land use change effects, many water quality and hydrology models is developed which usually are integrated with a GIS. A model of environmental non-point source watershed area (ANSWERS), Soil and Water Assessment Tool (SWAT), agricultural non-point sources (AGNPS), protecting the natural environment of the United States (NRCS) and long-term hydrology impact assessment (L-THIA) model are example of this models. This models can be used for impact assessment of land use management and other changes on hydrology and water quality. In this study L-THIA model was used for estimating runoff due to change in land use in Chaloos and Noshahr. This model is a good tool for potential impact assessment of land use change on surface runoff and water pollution and has been developed as accessible and rapid tools for using in long –time impact assessment of land use change. The core of this model based on curve number (CN) which is widely used for estimating the flow behavior in an urban watershed. Using CN equation in the L-THIA is a simple alternative for hydrology complex model that require a lot of data which often are not accessible for more areas. Failure to observe the river privacy and the removing excess sand from the river bottom , upward change in forest land use under the pretext of industrial development in Noshahr and Chaloos cities in addition to disturbance in the upstream Watersheds as result fluctuation in river input ,remind us the possibility of flood risk in heavy rainfall . Besides this issues, lack of proper urban development plan and uncontrolled heterogeneous construction in addition to making ugly face of the city, create a lot of costs for local people.For instance the costs caused by traffic and the fertile land further degradation and increased pressure on the environment can be named. On this study, long-term effects of land use change and urban development on hydrology conditions has been studied in Noshahr and Chaloos region.