پديد آورندگان :
اسفندياري درآباد، فريبا دانشگاه محقق اردبيلي - دانشكده علوم انساني - گروه جغرافياي طبيعي , مصطفي زاده، رئوف دانشگاه محقق اردبيلي - دانشكده كشاورزي و منابع طبيعي - گروه مرتع و آبخيزداري , فقه زاده، پيروزه دانشگاه محقق اردبيلي - دانشكده علوم انساني
كليدواژه :
استان آذربايجان غربي , Power Laws Analysis , دوره‌هاي كم‌آبي و پرآبي , تئوري Run , تغييرات دبي و رسوب
چكيده فارسي :
برآورد صحيح ميزان رسوبات حمل شده توسط جريان رودخانه در مديريت رودخانه‌ها و طراحي پروژه‌هاي حفاظت آب‌وخاك ضروري مي‌باشد. با توجه به تغييرات مقدار رسوب متناسب با دبي رودخانه، ارزيابي تغييرات زماني و مكاني تغييرات رواناب و رسوب مي‌تواند در تعيين و كنترل منشأ توليد رسوب مؤثر باشد. در پژوهش حاضر تغييرات ماهانه دبي و رسوب در 15 ايستگاه هيدرومتري، استان آذربايجان غربي در يك دوره آماري 20 ساله مورد تحليل قرارگرفته است. بر اساس ارتباط تغييرات بار رسوبي و دبي، از معادله خطي شده سنجه رسوب با تبديل لگاريتمي داده‌هاي دبي جريان و رسوب استفاده گرديد. سپس دوره‌هاي كم‌آبي و پرآبي با استفاده از تئوري Run تعيين گرديد، و به‌منظور تعيين الگوي وقوع دوره‌هاي كم‌آبي و پرآبي از روش Power Laws Analysis استفاده شد. نتايج پژوهش نشان داد كه حداكثر مقادير دبي و رسوب ايستگاه‌ها به‌صورت هم‌زمان و در فصل بهار (خصوصاً در ماه ارديبهشت) اتفاق افتاده است كه با مقادير بالاي بارندگي، ذوب برف بهاره و موجوديت رسوب در اين فصل در ارتباط بوده است. عليرغم اينكه بيش‌ترين مقدار دبي در ايستگاه ساري‌قميش 434/1 مترمكعب بر ثانيه بوده، اما برخلاف انتظار، بيش‌ترين مقدار رسوب در ايستگاه قاسملو 5174/9 تن در روز در طول دوره آماري مشاهده شد كه اين مورد بر عدم تبعيت حمل رسوب از مقدار بالاي دبي اشاره دارد. هم‌چنين بيش‌ترين دامنه تغييرات لگاريتم دبي و رسوب مربوط به ايستگاه پل‌بهراملو با مقادير 1/2 مترمكعب بر ثانيه و 2/3 تن در روز مي‌باشد. در ادامه مقادير وقوع تعداد و تكرار دوره‌هاي كم‌آبي و پرآبي در ايستگاه‌هاي مختلف با استفاده از پلات لگاريتمي دوگانه رسم شد، و مشخص شد كه در ايستگاه‌هاي موردمطالعه، تكرار دوره‌هاي كم‌آبي با رسوب پايين، بيش‌تر از تكرار دوره‌هاي پرآبي و مقادير رسوب بالا بوده است. بر اين اساس، دوره‌هاي كم‌آب با فراواني بيش‌تري اتفاق افتاده است كه نشان‌دهنده تمايل رفتار رودخانه‌ها به وضعيت فصلي بودن است و نيز تكرار بالاي دوره‌هاي كم‌رسوب نشان‌دهنده اين است كه در اكثر ماه‌هاي سال، ميزان رسوب جريان قابل‌توجه نيست. هم‌چنين تداوم دوره‌هاي پرآب و نيز دوره‌هاي كم‌رسوب بسيار بيش‌تر بوده است. بر اساس نتايج مي‌توان گفت كه در منطقه موردمطالعه، حمل مقادير بالاي رسوب مربوط به ماه‌هاي فروردين، ارديبهشت و خرداد محدودشده است. مقايسه پلات‌هاي لگاريتمي دوگانه نشان داد كه در ايستگاه‌هاي چپرآباد، دورود، نقده، اشنويه و پي‌قلعه تغييرات مقادير رواناب و رسوب در دوره‌هاي مختلف در يك راستا بوده ولي در ساير ايستگاه‌ها وقوع مقادير رواناب و رسوب هم‌زمان نبوده و از الگوهاي متفاوتي پيروي مي‌كنند.
چكيده لاتين :
Introduction:
The normal regimes of discharge and sediment load can be altered by the impact of natural variations and man-made disturbances. It is proved that temporal trends of discharge and sediment yield will occur due to anthropogenic impacts. Sediment transport via rivers is one of the important processes changing river morphology, bank stabilization, soil formation, and many other earth-related processes. Seasonality of water discharge controls the intermittently high sediment loads in rivers. Accurate estimation of sediment amount carried by the river flow is necessary for river management and to design of soil-water conservation projects. Also, according to the sediment variations based on changing river flows,assessment of spatio-temporal changes of runoff-sediment can be usefule in determining and cotrol of sediment source. The soil erosion phenomenon is the main cause of fertile soils losses from arable lands, also, the climatic conditions, hydrological, geological and excessive human pressure on the watersheds results carrying our more sediments in Iran.
Methodology:
In this study, the monthly changes of discharge and sediment yield were analysed in a 20-year period through 15 hydrometric stations in Azerbaijan Province, Iran. The monthly streamflow and sediment regime distributions over different months were investigated in a long-term observations over Azarbaijan Province. The linear sediment rating curve with a logharithmic transformation was used based on the discharge-sediment load relationship. The monthly streamflow and sediment load at the gauging stations were derived from the daily and random measured data, respectively. Then the wet-dry spells were determined using the Runs theory, and the occurrence pattern of wet and dry periods were recognised by using Power Laws Analysis techniqu. The results showed that the maximum discharge and sediment were observed in Spring season and especially in May, which can be related to occurrence of rainfall and snowmelt and high amount of river discharge. In other words, the highest and lowest amounts of sediment and discharge rates have been occurred in the spring and summer seasons. The high amounts of suspended sediment can be related with highe rainfalls in the spring season.
Results and Discussion:
According to the resuslts, it was found that the highest flow discharge was observed in Sarighamish station (434.1 cubic meters per secound), while the the maximum sediment rate has been occurred in Ghasemlou station having amount of 5174.9 tons per day. As well as, the Pole-Bahramlou station had the highest logarithm range of variation in monthly discharge and sediment load having 1.2 cubic meters per secound and 2.3 tons per day amounts. The slope of low sediment line had positive in the Plbe-Bahramlou, Sarighamish, Choplojeh, and Dizaj stations which indicates the frequency of occurrence in long periods of low sediment load in theses stations. The frequency and durations of wet and dry spells were drawn using double logarithmic plots. It was found that the dry periods waith low sediment yield were frequently occurred with respect to wet periods with high amount of sediment load. Also the wet spells with high sediment load had longer durations. Then, the frequency and durations of high and low sediment periods were represented on double-logarithmic plot to calculate the severity and duration of different periods of sediment transport. The results showed that the occurrence patterns of wet-dry spells and sediment transport rate were distinguished by using Power Laws Analysis technique.
Conclusions:
The monthly changes in discharge and sediment load in the study area can be explained by rainfall seasonality, characteristics of the watershed, hydrologic response behavior and land use (cultivation activities in agricultural lands) which are the main factors controlling components of discharge and suspended sediment load. The results proved that the patterns of wet and dry spell durations can be determined using power law technique. The changes from high to low sediment loads indicates that the decreasing sediment yield play important roles in characterizing changing sediment load during the rainy season. The interpretations of double logarithmic plots of (frequency versus length period) can be used to compare the occurrence patterns of high and low amounts of sediment in the stations over different discharge regimes. Further applications of power law method are suggested to obtain a better understanding for the interpretation of high and low amounts of sediment load and erosion regions in different climatic conditions. As a concluding remarks, the high value of sediment transport were observed in April, May and June. Based on comparison of double-logarithmic plots, the sediment variations were consistent with runoff variations in Chapar-abad, Doroud, Naghadeh, Oshnavieh and Peighale, while the remaining stations in the study area had inconsistent and different ouucurence patterns.
