Susurluk, gediz ve fırat-dicle havzalarında çevresel akış tahmini
Environmental flow estimation for susurluk, gedi̇z and euphrates-tigris basins
Yazar: DİLARA KARINCA
Danışman: PROF. DR. BİHRAT ÖNÖZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Hidrolik ve Su Kaynakları Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Çevre Mühendisliği = Environmental Engineering ; İnşaat Mühendisliği = Civil Engineering

Özet:
İnsanlığın medeniyet seviyesi arttıkça, enerji ve kentsel, tarımsal veya sanayii su, ihtiyacı artmaktadır. Ancak kaynakların sınırlılığı nedeniyle akarsuların insanlığa sağladığı sosyoekonomik faydalar ile akarsuyun sucul yaşamının ekolojik ihtiyaçları arasındaki dengenin sağlanması çok önemlidir. Bu nedenle sucul ekosistemin ihtiyaçlarının belirlenmesi ve bu ihtiyaçlara cevap verebilen çevresel akımın uygulanması, sürdürülebilir su kaynakları yönetiminin vazgeçilmezleridir.
Literatürde birçok çevresel akış belirleme yöntemleri vardır. Çevresel akış belirleme yöntemleri hidrolojik, hidrolik derecelendirme, habitat simülasyon, bütüncül olarak dört kategori altında toplanmıştır. Bu çalışmada, daha az veriye ve parasal kaynağa ihtiyaç duyduğu için hidrolojik yöntemlerin kullanılmasına karar verilmiştir.
Bu çalışma, Gediz, Susurluk ve Fırat-Dicle havzalarında su kaynaklarının sürdürülebilir yönetiminin planlamasına katkı sağlamak amacıyla yapılmıştır. Bu nedenle, bu havzalardaki çeşitli akarsuların doğal akımları incelenmiştir. Akarsuların aylık en kurak, en sulak ve ortalama akım hidrografları oluşturuldu. Gözlem süresinde görülmüş en kurak, en sulak ve ortalama yılların aylık akım hidrografları çizildi.
Bütün havzalardaki gözlenmiş verilerin sürekliliğini bozan verileri eksik olan yılların uygun yöntemler ile tamamlanması gerçekleştirildi. Bütün istasyonların 7-günlük minimum akım değerleri hesaplandı. Yedi günlük minimum akım tahminleri 2, 5 ve 10 yıllık dönüş aralıklarında iki ve üç parametreli log-normal ve Weibull ve üç parametreli log-normal ve genel ekstrem dağılımları kullanılarak gerçekleştirilmiştir. İstasyonların 7-günlük minimum akımlarına korelasyon, q-q çizimleri, hataların ortalama karekökü, taraflılık testleri uygulanmıştır. İstasyonların günlük akım verileri kullanılarak, debi süreklilik eğrileri çizilmiştir. Debi süreklilik eğrisinin %50, %70, %80, %90, %95 ve %99 aşılma oranlarına sahip olan debi değerleri bulunmuştur. Tennant yöntemine göre önerilen çevresel akışların hesaplanması için, yıllık ortalama debinin belirli yüzdeleri bulunmuştur. Ayrıca aylık ortalama akım değerlerinin %10'nun çevresel akış için uygun olabileceği düşünülerek bu yöntem de hesaplamalara katılmıştır. Temel akım yöntemi için istasyonların en güncel 10 yıllık akım verileri kullanılmıştır. Temel akım olarak adlandırılan yıllık olması gereken minimum akış miktarı ve temel akım rejimi metoduyla aylık çevresel akımlar hesaplanmıştır.
Susurluk Havzası için temel akım rejiminin kurak aylarda bile %90 aşılma yüzdesine karşılık gelen akım değerinin altına inmediği görülmüştür. Gediz Havzası'nda da bu yöntem ile hesaplanan çevresel akımların, kurak aylarda bile 5 yıllık tekerrür aralığına denk gelen 7-günlük minimum akım değerlerinin üstünde kaldığı saptanmıştır. Fırat-Dicle Havzası için hesaplanan temel akım rejiminin kurak aylarda bile 2 yıllık tekerrür aralığına denk gelen 7-günlük minimum akım değerine yakın seyrettiği görülmüştür. Fırat-Dicle Havzası'ndaki temel akım rejiminin aylık akım değerleri, yılın neredeyse bütün ayları için çevresel akım tahminlerinin en büyüğüdür. Bu çalışma kapsamında incelenen tüm havzalar için, temel akım rejimi akarsuyun ihtiyacı olan akım değişimini sağladığı görülmüştür. Ancak Gediz Havzası için sucul yaşamı korumaya yönelik yöntemin Tennant olduğu sonucuna varılmıştır. Susurluk ve Fırat-Dicle için Temel Akım en başarılı tahmin metodudur.

Abstract:
As the civilization level of humankind increases, urban, agricultural or industrial energy and water needs are increasing. Because of limited resources, it is very important to ensure a balance between the socio economic benefits provided by the rivers to ecological needs of aquatic life. Therefore, determining the needs of the aquatic ecosystem and the application of the environmental flow that can respond to these needs are indispensable for sustainable water resources management.
There are many environmental flow assessment methods in the literature. These are grouped under four categories; Hydrological, hydraulic rating, habitat simulation and holistic methods. In this study, environmental flows were estimated using hydrological methods, which are based on analysis historic streamflow data. Hydrological methods are the most popular technic because of low cost.
Daily flow data of 4, 9, 11 flow monitoring stations in Susurluk, Gediz and Euphrates-Tigris river basins, respectively, were used in the study. It has been studying with data of at least 46 years in the Susurluk Basin. The shortest observation period of stations in Gediz Basin is 14, the longest is 52 years. The shortest observation period in the Euphrates-Tigris Basin is 25 years.
This study was carried out to contribute to the planning of sustainable management of water resources in Gediz, Susurluk and Euphrates-Tigris river basins. For this reason, natural flows of several rivers in these basins have been studied. The monthly driest, wet and median stream hydrographs of the rivers were generated. These hydrographs were used to determine the difference between monthly maximum, minimum and median values. In addition, dry, wet and median years are determined according to the annual total water volume. Hydrographs that compared the driest, wet and median years of flow stations were plotted. In this way, the similarities between dry and wet years of rivers and the difference between median years of wet and dry years are examined. Then, environmental flow forecasts were made by hydrological methods.
By examining monthly median flow hydrographs, it is understood that the wet season is December to April for Susurluk Basin. It is observed that in wet season, monthly maximum and median flow values rises in similar way. However, the behavior of monthly minimum flows is independent from the dry and wet periods. In other words, it has been observed that the minimum value of the wet period may be smaller than the minimum value of the dry period.
All in all, April to December is Gediz Basin's wet period. During the dry season, the median flow values are very low, especially in summer. The monthly minimum flow values of the rivers are observed near-zero or zero in summer.
Euphrates-Tigris Basin's rivers, as distinct from Susurluk and Gediz, are fed from snow water. Accordingly, the wet period is not seen in the winter months, but in the spring and early summer, when the snow melts. High flow period for Euphrates-Tigris Basin is March to June. Monthly maximum and minimum flows increase in the wet period, but there are also exceptional cases in this regard. The months, when lowest monthly flows of Euphrates-Tigris Basin rivers are observed, mostly August, September or October. The driest month changes from river to river.
In the Susurluk Basin, the monthly flow values of the wet year are very different from the values of the median year in the winter months (from the December to the March), but this difference is very small in the summer and autumn (from November until July). The monthly flows difference, between median and dry year, is maximum at February and March. It has been observed that between July and November the flow values of the median and dry years at similar levels. The most common wet year observed in the Susurluk Basin is 1963. Drought years are different for each station.
Monthly flows of wet years of Gediz Basin rivers have reached very high levels for one or two months. Apart from these months, they have been observed similar levels with the median years monthly flows. Generally, in Gediz Rivers wet, median and dry years highest flow values are very different from each other. For D05A021, D05A041, E05A014 and E05A024 2001, for D05A028 and E05A023 1989, for D05A026 and D05A039 2007 have been the driest years. There are no common years between wet years.
In the Euphrates-Tigris Basin, the flow differences between the median years and the wet years suddenly rise in March, April and May. These months apart, median and wet years monthly flows are very close to each other. The difference between the median years and the dry years becomes apparent in the wet season, March, April, May and June. In July, August, September, October and November the wet, median and dry years and monthly flows are very close. In many basins throughout the basin, 1988 was the wet year. 2010 is the wet year for stations E21A049 and E21A054. 1983, 1989, 2001 and 2008 are common dry years.
The years, which daily flow data are missing, have been completed by appropriate methods. Statistical flow-frequency analysis method is calculated as the lowest flow for seven consecutive days within 2, 5, 10 year return periods. Estimates were made by using 2 parameter log-normal, Weibull and 3 parameter log-normal, GEV probability distribution functions. In order to test distribution functions according to observed flow data, correlation analysis, q-q plot, root mean square error and bias have been used.
Flow duration curve shows percent of time during which discharges were equaled or exceeded in time. Streamflow estimates Q50, Q70, Q80, Q90, Q95, Q99 were computed for 50, 70, 80, 90, 95, 99 percent probability of exceedances respectively. Tennant method that defines several percentages of the average annual flow according to aquatic life living conditions is also applied.
In addition, considering that 10% of monthly median flow values may be suitable for environmental flow, the method has also been included in the calculations. By using Basic Flow Method, the basic flow which is minimum discharge value for all year and monthly maintenance flow regime have been calculated.
It has been observed that the calculated main current regime for the Euphrates-Tigris basin is close to the 7-day minlow flow with 2- year return period even in the dry months. The monthly flow values of the basic flow regime in the Euphrates-Tigris Basin are the largest of the environmental flow estimates for almost the entire month of the year. For all basins studied in this study, Basic Flow Method is determined as appropriate hydrological environmental method for Susurluk and Euphrates-Tigris Basins. Tennant method is most suitable for Gediz Basin.
The following results were obtained for environmental flow estimation for Gediz, Susurluk and Euphrates-Tigris river basins.
i. The probability distribution that is determined as most suitable for Susurluk Basin is 3-Parameter Log Normal.
ii. For the other two basins, it is concluded that GEV is most successful distribution about prediction of 7-day low flows.
iii. 7 day low flow with 2, 5 and 10 year return period and Q80, Q95 and Q90 flows that are calculated by flow duration curve and 10% of annual average flow offer one environmental flow value for entire year.
iv. Tennant Method is to use seasonal time step. Tennant Method recommends proper environmental flows for wet and dry seasons of year.
v. The Basic Flow represents minimum flow that should flow in a river along the year. For determine environmental flow regime, Maintenance Basic Flow is to use monthly environmental flow prediction. Thus, temporal variability of environmental flow is procured. The environmental flow regime is found by using this method, follows similar patterns than natural flow regime.
vi. In addition, 10% of the monthly average flows are calculated to compare with other monthly methods.
vii. When comparing three basins, minimum Basic flows were obtained for Gediz Basin. Generally estimated values are very close or grater than 7 day low flow with 2 year return period.
viii. Environmental flow estimation methods that can respond to ecological needs are The Basic Flow Method for Susurluk and Euphrates-Tigris basins, fair or degrading condition range of Tennant Method for Gediz basin.
With this study, the need for environmental flow of Susurluk, Gediz and Fırat-Dicle basins has been approached more extensively. As things stand, it is important to esitimate environmental flow that correspond ecological needs. Different environmental flow methods have to be studied and compared in order to be able to respond to the ecological need in the most accurate way.