آشكارسازي تغييرات الگوي مكاني رودخانه هيرمند و تحليل مورفولوژيكي آن

Helmand River Spatial Pattern Changes Detection and Morphologic Analysis

هيرمند نام رودخانه‌اي حيات‎آفرين براي يكي از كانون‌هاي جمعيتي در گوشه شرقي كشور است كه در منتهي‌اليه خود بخشي از مرز مشترك ايران و افغانستان را به طول 30 كيلومتر تشكيل مي‌دهد. خشكسالي‌هاي پياپي و زيرساخت‌هاي خاص مورفولوژيكي، بستر مناسبي براي تغييرپذيري در الگوي هندسي و استقرار فضايي مجرا و مسير اصلي اين رودخانه فراهم كرده است. درك و استخراج اين تغييرات و معرفي ويژگي‌هاي مورفولوژيك آن، به‎سبب فراهم‎آوري تغيير در حدود مرزي و چالش در الگوي بهره‎برداري مشترك از آب آن، موضوع مهم و مورد توجه پژوهش حاضر است. براي اين امر، الگوي تغييرات مكاني رودخانه در نيم قرن گذشته (1344-1390)، از طريق تحليل تصاوير سنجش از دوري دو زمانه مورد بررسي قرار گرفت. در اين راستا، طول رودخانه با توجه به الگوي امروزي آن به 13 مقطع فضايي تقسيم و تغييرات هندسي رودخانه برپايه نقشه‎هاي بُرداري مستخرج از تصاوير مقدم و موخر در هر يك از اين مقاطع، به‎طور جداگانه مورد بررسي قرار گرفتند. يافته‌ها بيانگر رخداد تغيير در الگوي هندسي اغلب بخش‌هاي رودخانه است؛ به‎طوري كه در تمامي مقاطع مورد بررسي، محور رودخانه تغييرپذيري بين حداقل 5 تا حداكثر 31 درجه را تحمل كرده است. تغيير در الگوي فضايي رودخانه نيز به‎دنبال تغيير در الگوي هندسي آن شكل گرفته، به‎طوري كه سطح اشغال آن 5/31 درصد افزايش يافته و از رقم 9/1ميليون مترمربع در سال 1344، به بيش از 5/2 ميليون مترمربع در سال 1390 رسيده است . همچنين يافته‌هاي پژوهش نشان داد، به‎سبب تغيير در الگوي فضايي رودخانه، مقادير مشخصي از اراضي كشور در نوار مرزي واگذار و به‎طور متقابل، از اراضي همسايه به خاك كشور الحاق شده است. يافته‌هاي پژوهش درخصوص عوامل ايجابي تغيير در الگوي فضايي و هندسي رودخانه، علاوه‎بر تاييد و تاكيد بر عوامل ثابت محيطي، مسيله خشكسالي‌هاي پي‎درپي و انسداد بستر توسط ماسه‌هاي انباشته شده (حاصل از عمل باد) را عامل محوري و موثر اين تغييرات مي‌داند.

Introduction River border as a natural border between two or more international political units can effect on political relation between countries located in both side due to it’s morphological change. Helmand and Harierrod are two main rivers flowed along Iran and Afghanistan border. Helmand River located in eastern part of Iran, which is bring the life to the many population are settling in extreme part of Iran and Afghanistan border flows 30 km along the border. Severity of frequency drought along with morphological assistance caused the availability of change in geometry and spatial pattern of the river channel. The research is focus on this importance note that the change detection of this importance river can effect on some political challenge across the border as well as valuable water distributed between two countries. Methodology The research is based on pragmatic method which deals with lab work as well as field measurement and investigation. Furthermore, for extraction the channel morphology and pattern changes, the set of multisensory and multi-temporal remote sensing images cover period of above 55 years (1955 -2012) were provide. The aerial photographs of 1955 in scale of 1/50000 were converted to digital. The geocode photos were mosaic based on GCP collected from field. The out com vector map of river channel was provide using the ARCGIS software. The stereo images of Cartosat satellite data related to year of 2012 were processed for orthoimage generation and river channel drawing. The two out com vector map were analysis on Atou CAD and ARCGIS software for change detection extraction. Results and Discussion In order to extract the change detection of river, the river channel was slicing in 13 parts based on its present morphology patterns. The primary (1955) and secondary (2012) vector maps of channel were extract and analysis for change detection over the all 13 part. The outcome was shown that, the main channel axis was rotated from 5 t0 13 degree in all 13 parts. Moreover, the area extend of river bed was increased from 1.9 MSq in 1955 to 2.5 Msq in 2012. Furthermore, the result outcome showed that river channel bed occupied 0.681 sqkm2 of west coast and 0.456 sqkm2 in east side. The result also showed sand movement and deposition in dray bed of river due to severity of continues drought as main factor to changes the geometry and pattern of this river. Conclusion The change of river morphology pattern is caused several changes in border line and country side land between both sides of river. Border change in this high sencivity area can effect overt the international political relation between two countries. Moreover, the assessable of water in this dray area can change due to its very low slop angle plane.