Low flow analysis in the Seyhan Basin

Öz

In this study low-flow analysis was conducted at various measurement stations within the Seyhan Basin. Low-flow frequency analysis was performed to estimate the drought risks in the short, medium, and long term using annually-averaged minimum discharge values corresponding to durations of d = 1, 7, 10, and 15 days. Low-flow estimates for different return periods were obtained using both two-parameter distributions, namely Log-Normal (LN2), Gamma (G2), Weibull (W2), Exponential (E2), Gumbel (GEV-I), and Logistic (L2), and three-parameter distributions, namely Generalized Extreme Value (GEV-III), Log-Normal (LN3),Pearson Type III (P3), Log-Pearson Type III (LP3), and Generalized Logistic (GL3). The goodness-of-fit between the various probability distributions and observed time series was investigated using the Kolmogorov-Smirnov (K–S) test. To observe trends in the low flows estimated by these distributions, various statistical tests were applied, including the Mann-Kendall (MK), Trend-Free Pre-Whitening (TFPW), and innovative trend analysis (ITA). The results obtained using measurements from six different stations indicate that the most accurate estimations for the Seyhan Basin were obtained using the P3, GEV-III, and LN3 distributions. At the designated significance level, a decreasing trend was observed at three stations. For the remaining stations where no statistically significant trend was identified, ITA tests revealed a negative trend. Based on these findings, it can be concluded that the flow rates measured at these stations have substantially decreased, suggesting a potential drought risk in the region.

Anahtar Kelimeler

• Seyhan Basin
• Low-flow analysis
• Drought risk

Seyhan Havzası’nda düşük akımların analizi

Öz

Bu çalışmada Seyhan Havzası’nda yer alan istasyonlarda düşük akım analizi gerçekleştirilmiştir. Bu doğrultuda kısa, orta ve uzun vadeli kuraklık tespiti için d = 1, 7, 10 ve 15 günlük yıllık ortalama minimum debi değerleri kullanılarak düşük akım frekans analizi yapılmıştır. İki parametreli Log-Normal (LN2), Gamma (G2), Weibull (W2), Üstel (E2), Gumbel (GEV-I), Lojistik (L2) dağılımları ile üç parametreli GEV (GEV-III), Log-Normal (LN3), Pearson Tip III (P3), Log-Pearson Tip III (LP3) ve Genel Lojistik (GL3) dağılımları kullanılarak farklı dönüş aralıklarına sahip düşük akım tahminleri gerçekleştirilmiştir. Kolmogorov-Smirnov (K-S) uygunluk testi ile farklı istatistiksel dağılımların mevcut zaman serilerine uygunluğu tespit edilmiştir. Elde edilen düşük akımlardaki eğimin (trend) belirlenmesi için Mann-Kendall (MK), Trend-Free Pre-Whitening (TFPW) ve yenilikçi trend analizi (ITA) testleri uygulanmıştır. Çalışmada altı farklı istasyon ölçümleri kullanılarak elde edilen bulgular, Seyhan Havzası’nda en iyi tahminlerin LN2, P3, GEV-III ve LN3 dağılımları ile elde edildiğini göstermiştir. Seçilen anlamlılık düzeyinde üç istasyonda azalan trend bulunmuş olup, anlamlı bir trend tespit edilemeyen diğer istasyonlarda ITA testleri ile azalan bir eğilim belirlenmiştir. Elde edilen bulgular doğrultusunda, bu istasyonlarda özellikle son 10-15 yıllık süreçte ölçülen debilerin önemli miktarda azaldığı ve dolayısıyla küresel iklim değişikliği de göz önüne alındığında kuraklık riskinin olabileceği sonucuna ulaşılmıştır.

Anahtar Kelimeler

• Seyhan Havzası
• Düşük akım analizi
• Kuraklık riski

Kaynakça

1. Yevjevich, V., Methods for determining statistical properties of droughts, Coping with droughts, Water Resources Publications, 22-43, Colorado, (1983).
2. Bayazıt, M. ve Önöz, B., Taşkın ve Kuraklık Hidrolojisi, Nobel Yayın Dağıtım, Ankara, (2008).
3. Vogel, R. M. ve Kroll, C. N., Regional geohydrologic-geomorphic relationships for the estimation of low-flow statistics, Water Resources Research, 28, 9, 2451-2458, (1992).
4. Mishra, A. K. ve Singh, V. P., Drought modeling-a review, Journal of Hydrology, 403, 1-2, 157-175, (2011).
5. Smakhtin, V. U., Low flow hydrology: a review, Journal of Hydrology, 240, 3-4, 147-186, (2001).
6. Tallaksen, L. M. ve Van Lanen, H. A., Hydrological drought: processes and estimation methods for streamflow and groundwater, 2. basım, Elsevier, Cambrigde, (2023).
7. Laaha, G. ve Blöschl, G., A comparison of low flow regionalisation methods-catchment grouping, Journal of Hydrology, 323, 1-4, 193-214, (2006).
8. Önöz, B. ve Bayazıt, M., GEV-PWM model for distribution of minimum flows, Journal of Hydrologic Engineering, 4, 3, 289-292, (1999).

9. Eriş, E., Aksoy, H., Önöz, B., Çetin, M., Yüce, M. İ., Selek, B., Aksu, H., Burgan, H. İ., Eşit, M., Yıldırım, I. ve Ünsal Karakuş, E., Frequency analysis of low flows in intermittent and non-intermittent rivers from hydrological basins in Turkey, Water Supply, 19, 1, 30-39, (2019).
10. Yılmaz, S. U., Çiltaş, E., Eldayıh Kanber, Y., Bakar, H., Öz, M., Kaçar, F. S. ve Önöz, B., Seyhan Havzası etrafında düşük akım frekans analizi ve kurak dönem analizi, 12. Ulusal Hidroloji Kongresi, 301-311, Samsun, (2024).
11. Massey, F. J. J., The Kolmogorov-Smirnov test for goodness of fit, Journal of the American Statistical Association, 46, 253, 68-78, (1951).
12. Anderson, T. W. ve Darling, D. A., Asymptotic theory of certain "goodness of fit" criteria based on stochastic processes, The Annals of Mathematical Statistics, 193-212, (1952).
13. Kroll, C. N. ve Vogel, R. M., Probability distribution of low stream-flow series in the United States, Journal of Hydrologic Engineering, 7, 2, 137- 146, (2002).
14. Yue, S. ve Wang, C., The Mann-Kendall test modified by effective sample size to detect trend in serially correlated hydrological series, Water Resources Management, 18, 3, 201–218, (2004).
15. Şen, Z. Innovative trend analysis methodology, Journal of Hydrologic Engineering, 17, 9, 1042-1046, (2012).
16. Yue, S., Pilon, P. ve Cavadias, G. Power of the Mann–Kendall and Spearman’s rho tests for detecting monotonic trends in hydrological series, Journal of Hydrology, 259, 1-4, 254-271, (2002).
17. Burn, D. H. ve Elnur, M. A. H., Detection of hydrologic trends and variability, Journal of Hydrology, 255, 1-4, 107-122, (2002).
18. Özfidaner, M., Şapolyo, D. ve Topaloğlu, F., Hydrological drought analysis of streamflow data in Seyhan basin, Journal of Soil Water, 7, 1, (2018).
19. Altın, T. B., Sarış, F. ve Altın, B. N., Determination of drought intensity in Seyhan and Ceyhan River basins, Turkey, by hydrological drought analysis, Theoretical and Applied Climatology, 139, 95-107, (2020).
20. Terzi, T. B. ve Önöz, B., Drought analysis based on nonparametric multivariate standardized drought index in the Seyhan River basin, Natural Hazards, 1-28, (2025).
21. Von Storch, H. and Navarra, A., Misuses of statistical analysis in climate research, Analysis of Climate Variability: Applications of Statistical Techniques, Springer-Verlag, New York, 11-26, (1995).
22. Önöz, B. ve Bayazıt, M., The power of statistical tests for trend detection, Turkish Journal of Engineering & Environmental Sciences, 27, 4, 247-251, (2003).
23. Yue, S. ve Wang, C. Y., Applicability of prewhitening to eliminate the influence of serial correlation on the Mann-Kendall test, Water Resources Research, 38, 6, 4-1-4-7, (2002).