ارزيابي روش RVA به منظور تعيين مقادير جريان محيطزيستي رودخانه پلنگ‌ور جهت حفظ ارزش‌هاي اکولوژيکي و مقايسه آن با رويکردهاي هيدرولوژيکي
محورهای موضوعی : مدیریت منابع آبسیدمصطفی ابراهیم‌نیا 1 , هادی مدبری 2 , مرتضی کریمی 3 , بهناز ختار 4
1 - دانش آموخته کارشناسي ارشد مهندسي عمران سازه‌هاي هيدروليکي، موسسه آموزش عالي جهاد دانشگاهي رشت، ايران.
2 - استاديار گروه پايش منابع آب، پژوهشکده محيط زيست جهاد دانشگاهي، رشت، ايران.
3 - پژوهشگر گروه پايش منابع آب، پژوهشکده محيط زيست جهاد دانشگاهي، رشت، ايران.
4 - دانش آموخته دکتري مهندسي آب، دانشکده کشاورزي و منابع آب دانشگاه امام خميني (ره) قزوين، ايران.
کلید واژه: نياز آبي محيط زيستي, مديريت اکوسيستم رودخانه, روش محدوده تغييرپذيري جريان, رودخانه پلنگ‌ور,
چکیده مقاله :
زمينه و هدف: اثرات عوامل طبيعي و انساني بر تغييرات چرخه‌هاي هيدرولوژيکي در حوضه‌هاي آبريز سبب تهديد در امنيت و سلامت اکوسيستم‌هاي آبي و کاهش تنوع زيستي در رودخانه‌ها و تالاب‌ها شده است. در ساليان اخير به منظور حفظ اکوسيستم‌هاي طبيعي، کارکردها و خدمات وابسته به آنها توجه فزاينده‌اي به ارزيابي جريانات محيطزيستي در اين زيست‌بوم‌ها شده است. مقاله حاضر با هدف برآورد نياز آبي محيط زيستي رودخانه پلنگ‌ور با استفاده از روشهاي اکوهيدرولوژيکي ساده که علاوه بر خصوصيات هيدرولوژيکي ويژگيهاي اکولوژيکي رودخانه را نيز در نظر مي‌گيرد، صورت پذيرفت.
روش پژوهش: در اين تحقيق ابتدا به دليل وجود شرايط اکولوژيکي مختلف و تنوع زيستگاهي متفاوت در بالادست و پايين دست رودخانه پلنگ‌ور از داده‌هاي 2 ايستگاه هيدرومتري مسجدپيش در بالادست و کلسر در پايين‌دست استفاده شد. سپس پارامترهاي موثر هواشناسي مانند بارش، دوره‌هاي ترسالي و خشکسالي مورد تجزيه و تحليل قرار گرفت و با محاسبه رژيم هيدروليکي جريان، مقادير دبي جريان در رودخانه در ماه‌هاي مختلف سال تحليل گرديد. در مرحله بعد جريان زيست‌محيطي رودخانه به صورت ماهانه از روش منحني تغييرپذيري در شرايط حداقل و حداکثر محاسبه شد و با نتايج حاصل از ساير روشهاي هيدرولوژيکي مانند روشهاي تنانت، تگزاس، تگزاس اصلاح‌شده و انتقال منحني تداوم جريان مقايسه گرديد.
يافته‌ها: مقادير جريان محيطزيستي برآورد شده از روش RVA در رودخانه پلنگ‌ور در دو ايستگاه هيدرومتري مسجدپيش در بالادست و کلسر در پايين‌دست به ترتيب در شرايط حداقل جريان محيطزيستي برابر 84/0 و 01/5 مترمکعب بر ثانيه و در شرايط حداکثر جريان محيطزيستي برابر 4/1 و 69/9 مترمکعب بر ثانيه به دست آمد. مقادير برآورد شده جريان محيطزيستي در شرايط حداقل در ايستگاه مسجدپيش نشان مي‌دهد که روش RVA مي‌تواند شرايط اکولوژيکي رودخانه را در بخشي از سال به طور کامل حفظ نمايد زيرا در ماه‌هاي شهريور تا ارديبهشت عددي بين 60 تا 80 درصد ميانگين ماهانه را دربرمي‌گيرد. اما در ماه‌هاي خرداد، تير و مرداد که افزايش برداشت آب از رودخانه به دليل مصارف کشاورزي زياد است عملا روش RVA حدود 20 تا 40 درصد متوسط جريان را درنظرگرفته است که اين مقدار اگرچه با شرايط مناسب کمي فاصله دارد اما با توجه به شرايط محيطي و مديريت تخصيص منابع آب، مي‌تواند مقداري قابل قبول براي حفظ شرايط اکولوژيکي حداقلي در رودخانه باشد. همچنين نتايج مقادير برآورد شده جريان محيطزيستي در شرايط حداقل در ايستگاه کلسر در پايين‌دست رودخانه نشان داد که روش RVA مي‌تواند شرايط اکولوژيکي رودخانه را حفظ نمايد زيرا در کل سال حتي در ماه‌هاي گرم و بحراني توانسته است عددي بين 55 تا 80 درصد ميانگين ماهانه را دربربگيرد. مقادير برآورد شده از ساير روشهاي هيدرولوژيکي استفاده شده در اين مطالعه نتوانست جوابگوي نياز آبي محيطزيستي در رودخانه در ماه‌هاي گرم سال باشد.
نتايج: در شرايط کمبود داده، استفاده از مقادير برآورد شده از روش محدوده تغييرپذيري جريان در شرايط حداقل ميانگين مي‌تواند با ارائه مقادير منطقي، شرايط اکولوژيکي رودخانه را تا حد زيادي حفظ نمايد. از آنجا که زمان اصلي تخمريزي ماهيان در زيست بوم پلنگ‌ور در ماه‌هاي اسفند، فروردين و ارديبهشت است لذا نتايج حاصل از روش RVA در شرايط حداقل در هر دو ايستگاه بالادست و پايين دست توانسته است به خوبي شرايط مناسب براي اين کارکرد مهم اکولوژيکي را حفظ نمايد و ضمانت علمي کامل براي اين ارزش اکولوژيکي يعني حفظ عمليات تخمريزي ماهيان در اين منطقه باشد. همچنين استفاده از روشهاي RVA در شرايط حداکثر و روش FDC-shifting در ماه‌هاي سرد سال يعني از ماه مهر تا ارديبهشت به دليل ارائه مقادير نزديک به ميانگين و يا حتي بيشتر از آن توصيه مي‌شود. اما در ماه‌هاي بحراني سال به ترتيب استفاده از روشهاي RVA در شرايط حداقل، روش تگزاس اصلاح شده، روش تگزاس و روش FDC-shifting توصيه مي‌گردد.
Background and Aim: The effects of natural and human factors on changes in hydrological cycles in watersheds have threatened the safety and health of aquatic ecosystems and reduced biodiversity in rivers and wetlands. In recent years, in order to preserve natural ecosystems, functions and services related to them, increasing attention has been paid to the evaluation of environmental flows in these ecosystems. The present paper was carried out with the purpose of estimating the environmental water demand of Palangver river using simple ecohydrological methods that take into account the ecological characteristics of the river in addition to the hydrological characteristics.
Research Method: In this research, due to the existence of different ecological conditions and different habitat diversity in the upstream and downstream of Palangver river, the data of 2 hydrometric stations of Masjedpish in the upstream and Kolesar in the downstream were used at first. Then the effective meteorological parameters such as precipitation and the periods of wet and drought year were analyzed and by calculating the hydraulic regime of the flow, the flow rates in the river were analyzed in different months of the year. In the next step, the environmental flow of the river was calculated on a monthly basis using the variability curve method in minimum and maximum conditions and compared with the results of other hydrological methods such as Tennant, Texas, modified Texas and transfer of flow continuity curve methods.
Findings: The environmental flow values estimated by the RVA method in the Palangver River at two hydrometric stations of Masjedpish in the upstream and Kolesar in the downstream, in the conditions of minimum environmental flow were obtained 0.84 and 5.01 cubic meters per second, and in the conditions of maximum environmental flow were obtained 1.4 and 9.69 cubic meters per second, respectively. The estimated values of the environmental flow in minimum conditions at Masjidpish station show that the RVA method can completely maintain the ecological conditions of the river in a part of the year, because in the months of September to May, it covers a number between 60 and 80% of the monthly average. But in the months of June, July and August, when water withdrawal from the river is increased due to the agricultural uses, the RVA method has considered about 20-40% of the average flow; although this amount is far from the ideal conditions, it can be an acceptable amount to maintain minimum ecological conditions in the river considering the environmental conditions and water resource allocation management.
Also, the results of the estimated values of the environmental flow in the minimum conditions at Kolesar station in the downstream of the river showed that the RVA method can maintain the ecological conditions of the river because in the whole year, it has been able to include a number between 55 and 80% of the monthly average even in hot and critical months.
Results: In the condition of lack of data, using the values estimated from the flow variability range method in minimum average conditions can maintain the ecological conditions of the river to a large extent by providing reasonable values. Since the main spawning time of fishes in the Palangver ecosystem is in the months of March, April and May, therefore the results of the RVA method have been able to maintain the suitable conditions for this important ecological function in the minimum conditions in both upstream and downstream stations and the full scientific guarantee for this ecological value is to maintain fish spawning operations in this area. It is also recommended to use RVA methods in the maximum conditions and FDC-shifting method in the cold months of the year, i.e. from October to May, due to providing values close to the average or even higher. But in the critical months of the year, it is recommended to use RVA methods in the minimum conditions, modified Texas method, Texas method and FDC-shifting method respectively.
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