برآورد عمر مفید مخزن سد‌نگارستان با ترسیم منحنی هیپسومتریک به‌‌روش strahler اصلاح‌شده و تصاویر ماهواره‌ای

مقالات آماده انتشار

نوع مقاله : مقالات پژوهشی

نویسندگان

• عبدالرضا ظهیری ¹
• خلیل قربانی ²
• حامد فیض آبادی ³
• حسین شریفان ⁴

¹ دانشگاه علوم کشاورزی و منابع طبیعی گرگان

² دانشیار گروه مهندسی آب، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران.

³ فارغ التحصیل کارشناسی ارشد علوم و مهندسی آب، دانشگاه علوم کشاورزی و منابع طبیعی گرگان

⁴ دانشیار گروه مهندسی آب، دانشگاه علوم کشاورزی و منابع طبیعی گرگان، گرگان، ایران

10.22067/jsw.2024.89646.1432

چکیده

مخازن سدها از منابع حیاتی تأمین‌آب جوامع بشری محسوب می‌شوند که آگاهی‌داشتن از مقدار حجم آب ذخیره‌شده در آن‌ها امری ضروری‌است. استفاده از اشل و منحنی حجم-سطح-ارتفاع مخزن که به‌کمک عملیات نقشه‌برداری تهیه می‌شود، روش معمول برای تخمین ظرفیت ذخیره‌سازی مخازن می‌باشد. با گذشت‌زمان و وقوع رسوب‌گذاری‌های متعدد، منحنی حجم-سطح-ارتفاع مخزن تغییر می‌کند که استفاده مجدد از آن نیازمند تصحیح این منحنی است. عملیات هیدروگرافی مخازن با‌استفاده از ابزاری مثل اکوساندر روشی مرسوم برای تصحیح این منحنی‌است که علاوه بر پرهزینه بودن، زمان‌بر نیز می‌باشد. در سال‌های اخیر مطالعات مختلفی برمبنای سنجش‌از‌دور با هدف تخمین حجم آب‌ذخیره‌شده در مخازن، به‌محاسبه سطوح آب برای ترسیم منحنی حجم-سطح-ارتفاع پرداخته‌اند. اساس کار این مطالعات تفکیک پهنه‌های آب‌وخشکی به‌کمک شاخص‌های طیفی، محاسبه سطوح‌آب و ترسیم منحنی‌های سطح-‌ارتفاع مخازن با‌استفاده از روابط خطی یا چندجمله‌ای‌ها می‌باشند. محدودیت این روش‌ها عدم‌دقت مناسب روابط خطی یا ‌چندجمله‌ای در برازش منحنی سطح‌-ارتفاع مخزن برای نقاط ابتدایی و انتهایی بازه تغییرات عمق‌‌آب ‌است. در این پژوهش با هدف رفع‌محدودیت‌ روابط خطی و چند‌جمله‌ای برای پیش‌بینی دقیق نقاطی از منحنی سطح‌-ارتفاع مخزن که داده‌های مشاهداتی به‌دلیل عدم وقوع موجود نیستند، از ترسیم منحنی هیپسومتریک به‌روش استرالر اصلاح‌شده استفاده شده‌است. با‌استفاده از منحنی هیپسومتریک می‌توان ظرفیت ذخیره‌سازی مخزن بین سطوح‌آب متوالی را محاسبه کرد و حجم‌نهایی آب ذخیره‌شده در آن‌را به‌دست آورد. براین اساس با مقایسه حجم آب ذخیره‌شده در زمان فعلی و ظرفیت ذخیره‌سازی طراحی‌مخزن در زمان شروع بهره‌برداری، نرخ رسوب‌گذاری و عمرمفید مخزن سد نگارستان برآورد شد. نتایح نشان‌داد که در بازه‌زمانی 9 ساله، ظرفیت ذخیره‌ مخزن در تراز سطح آب حدود 5/189 متر که معادل تراز تقریبی تاج سرریز می‌باشد، از حدود 24 به 20 میلیون‌مترمکعب کاهش یافته‌است که بر‌این اساس نرخ متوسط رسوبگذاری سالانه مخزن حدود 6/1 درصد برآورد شد. همچنین در این‌مدت، تراز کف‌ مخزن سد نگارستان به‌دلیل انباشته‌شدن رسوبات به طور متوسط حدود 10 متر افزایش داشته-است و کمترین تراز کف‌مخزن از 160 به حدود 170 متر رسیده‌است. مطابق نتایج به‌دست‌آمده از این پژوهش و با فرض ثابت‌ بودن شرایط اقلیمی، عمرمفید مخزن سد نگارستان از ابتدای سال 1403 حدود 53 سال برآورد‌شد.

کلیدواژه‌ها

• سنجش‌از‌دور
• ظرفیت‌ذخیره
• لندست 8
• مخزن سد
• نرخ رسوب‌گذاری

موضوعات

• علوم آب

عنوان مقاله [English]

Assessment of useful life of Negarestan reservoir dam using hypsometric curve by modified strahler method and satellite imagery

نویسندگان [English]

• Abdolreza Zahiri ¹
• Khalil Ghorbani ²
• Hamed Feiz Abady ³
• Hossein Sharifan ⁴

¹

² Associated Prof, Water Engineering Department, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

³ Msc Student, in Water Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran.

⁴ Associated Prof, Water Engineering Department, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

چکیده [English]

Introduction: The reservoirs are considered as vital sources of water supply for human societies, hence the correct and planned management of their reserves is an essential issue. Dams are used for purposes such as urban water supply, irrigation of agricultural lands, floods control and hydroelectric power generation. In order to properly manage and monitor the consumption of these important reserves, it is inevitable to know their capacities. Using water stage and the reservoir's initial volume-area-elevation curve, which is prepared with the hydrographic operations, is a common method for estimating the storage capacity of reservoirs at different water levels. Over time and the occurrence of numerous sedimentations that can occur due to factors such as floods, the initial volume-area-elevation curve of the reservoir changes, hence it needs to be modified.The hydrographic operation of reservoirs using tools like Eco-sounders is a conventional method for correction of this curve, which is not only expensive but also time-consuming. In recent years, various studies based on remote sensing with the aim of estimating the volume of water stored in reservoirs have calculated water levels to establish the surface area-elevation curve. The basis of these studies are the separation of water-lands masks with the help of spectral indices, the calculation of water levels, and the developing of reservoir surface area-elevation curves using linear or polynomials relationships. The main limitation of these methods is the inaccuracy of linear or polynomial relationships in fitting the surface area-elevation curves of the reservoir for the beginning and end points of the water stage change interval, which corresponds to the empty or fullness of the reservoir. and these happen due to the occurrence of factors such as drought or floods.In this research, with the help of to eliminating the limitation of linear and polynomial relationships for accurately predicting the points of the reservoir surface area-elevation curves where the observational data are not available due to non-occurrence, by drawing the hypsometric curve using the Modified Strahler method has been used. By using the hypsometric curve, it is possible to calculate the storage capacity of the reservoir between successive water levels and obtain the final volume of water stored in it. In this study, by comparing the volumes of water stored at the present and initial reservoir capacities, the sedimentation rate and the useful life of the reservoir of Negarestan dam have been estimated.

Material and Methods: Negarestan Dam (Kabudval) is located on the Qara Su (Zarin Gol) river, and 45 km east of the city of Gorgan in the Golestan province. This dam is used for purposes such as supplying urban water to Aliabad city and supplying water needed for the agricultural irrigation network of Qarasu. In this srudy, landsat8 satellite images were used to estimate the useful life of the Negarestan reservoir. The required images of the ROI were downloaded through the USGS database and pre-processed in Envi5.3 software. Using visible and infrared spectral bands, water indices NDWIMCFeeters, NDWIGao, MNDWI, AWEISh and TCWet were calculated to separate land-water masks. After evaluating the accuracy of the obtained water level results by comparing it with the initial volume-area-elevation curve of Negarestan reservoir, the MNDWI index was used as the most accurate index to calculate water levels.In this study, the modified Strahler method was used to obtain the hypsometric curve of the surface area-elevation of the reservoir, which has high accuracy in extrapolating the beginning and end points of the curve. By using the hypsometric curve, water level levels were extracted for arbitrary water levels and with the help of the prismoidal method relation of the volume between consecutive water levels, the sum of these volumes is equal to the current storage capacity of the reservoir. To estimate the sedimentation rate of the Negarestan dam reservoir, the current storage capacity of the reservoir was compared with the initial storage capacity in 2015, and based on this, the useful life of the reservoir was accurately predicted.

Results and Discussion: Validation results for calculating water surface areas using NDWIMCFeeters, NDWIGao, MNDWI, AWEISh and TCWet water indices showed that the MNDWI index with an average water surface areas calculation error equal to 5% is more accurate than other indices. Therefore, MNDWI index was used in this study. Also, the comparison of the volume of water stored in the Negarestan reservoir with its initial storage capacity at the time of operation showed that in a period of 9 years, the storage capacity of the reservoir (at the water level equal to about 189.5 meters), which is equivalent to the approximate level of the overflow crest. It has decreased from about 24 to 20 million cubic meters, based on which the average annual sedimentation rate of the reservoir was estimated to be about 1.6%. The results showed that in a period of 9 years, the average level of the bathymetry of Negarestan reservoir has increased by 10 meters due to the accumulation of sediments, and the minimum level of the batymetry has reached from 160 to about 170 meters.According to the statistics of the International Commission on Large Reservoirs (ICOLD), the average annual sedimentation rate of the world's reservoirs is reported to be about 0.95%, and the results show that this amount in the Nagaristan Dam reservoir is almost 2 times the average rate. It is universal. According to the results obtained from this research and assuming constant climatic conditions, the useful life of the Nagarestan dam reservoir was estimated to be about 53 years from the beginning of 2024.

Conclusion: Considering the increasing importance of water resources management, including dam reservoirs, in this study, a fast and inexpensive method based on remote sensing is used to calculate the volume of water stored in dam reservoirs and estimate the useful life. They were presented. In addition to the appropriate accuracy, this method was able to overcome the limitations of the previous methods in estimating the volume of accumulated sediment in the deep parts of the reservoir and can be used for the correct management of water resources.

کلیدواژه‌ها [English]

• dam reservoir
• Landsat8
• Remote sensing
• storage capacity
• sedimentation rate