Dicle Barajı Su Alma Yapısında Periyodik Su Kalitesi Değişimleri ve Sentinel-2 Tabanlı NDWI ile NDTI İndekslerinin Sınırlılıkları

Abstract

Bu çalışmada, 2022–2025 yılları arasında Ocak, Mart, Haziran ve Eylül aylarında Dicle Barajı su alma yapısından alınan 16 su örneğine ait fizikokimyasal ve mikrobiyolojik su kalitesi verileri, Sentinel-2A uydu görüntülerinden türetilen Normalize Edilmiş Fark Su İndeksi (NDWI) ve Normalize Edilmiş Fark Bulanıklık İndeksi (NDTI) ile birlikte değerlendirilmiştir. Elektriksel iletkenlik, pH, sülfat, bulanıklık, renk, su sıcaklığı, toplam koliform ve fekal koliform parametrelerindeki periyodik farklılıklar, yıllar blok değişkeni olarak ele alınarak kesin (exact) Friedman testi ile incelenmiş; çoklu karşılaştırmalardan kaynaklanan Tip I hata olasılığını kontrol etmek amacıyla Holm düzeltmesi uygulanmıştır. Elektriksel iletkenlik, pH, sülfat, bulanıklık, renk parametreleri ile optik indeksler arasındaki ilişkiler Pearson ve Spearman korelasyon analizleri kullanılarak değerlendirilmiştir. Uzun yıllara ait meteorolojik normaller ise yalnızca çalışma alanının iklimsel özelliklerini tanımlamak amacıyla kullanılmıştır. Holm düzeltmesi sonrasında, örnekleme dönemleri arasında yalnızca su sıcaklığı ve toplam koliform parametrelerinde istatistiksel olarak anlamlı farklılık belirlenmiştir. Toplam koliform için elde edilen Kendall'ın W katsayısının 1,000 olması, örnekleme dönemlerinin sıralamasının dört yıl boyunca tamamen aynı olduğunu göstermektedir. NDWI ile incelenen su kalitesi parametrelerinin hiçbiri arasında istatistiksel olarak anlamlı bir ilişki saptanmamıştır. NDTI açısından ise yalnızca elektriksel iletkenlik ile olan ilişkinin hem Pearson (r = 0,7649; düzeltilmiş p = 0,0056) hem de Spearman (ρ = 0,7432; düzeltilmiş p = 0,0097) analizlerinde anlamlılığını koruduğu belirlenmiştir. Bununla birlikte, elektriksel iletkenliğin doğrudan optik olarak aktif bir parametre olmaması ve söz konusu ilişkinin yalnızca 16 gözleme dayanması nedeniyle, bu bulgu öngörücü bir model olarak yorumlanmamıştır. Elde edilen sonuçlar, NDWI ve NDTI indekslerinin laboratuvar analizlerinin yerine geçemeyeceğini; ancak daha kapsamlı arazi gözlemleri ve bağımsız doğrulama verileri ile desteklenmeleri durumunda su kalitesinin izlenmesinde tamamlayıcı araçlar olarak kullanılabileceklerini ortaya koymaktadır.

Keywords

• Dicle Barajı
• su kalitesi
• Sentinel-2A
• Normalize Edilmiş Fark Su İndeksi (NDWI)
• Normalize Edilmiş Fark Bulanıklık İndeksi(NDTI)

Ethical Statement

Bu çalışma, insan katılımcılar, deney hayvanları veya etik kurul onayı gerektiren herhangi bir deneysel uygulama içermemektedir. Su örnekleri, Dicle Barajı su alma yapısından rutin çevresel izleme çalışmaları kapsamında toplanmış olup, insanlar, hayvanlar veya koruma altındaki ekosistemler üzerinde herhangi bir müdahalede bulunulmamıştır. Yazar, çalışmanın araştırma dürüstlüğü ve bilimsel yayın etiği ilkelerine uygun olarak yürütüldüğünü beyan etmektedir.

Periodic Water-Quality Variation at the Dicle Dam Intake and the Limitations of Sentinel-2-Derived NDWI and NDTI

Abstract

This study jointly evaluated physicochemical and microbiological water-quality data from 16 samples collected at the Dicle Dam intake structure in January, March, June, and September between 2022 and 2025, together with the Normalized Difference Water Index (NDWI) and Normalized Difference Turbidity Index (NDTI) derived from Sentinel-2A imagery. Periodic differences in electrical conductivity, pH, sulfate, turbidity, color, water temperature, total coliform, and fecal coliform were examined using an exact Friedman test, with years treated as blocks, and Holm correction was applied for multiple testing. Relationships between electrical conductivity, pH, sulfate, turbidity, color, and the optical indices were evaluated using Pearson and Spearman correlation analyses. Long-term meteorological normals were used only to describe the climatic characteristics of the study area. After Holm correction, only water temperature and total coliform differed significantly among the sampling periods. A Kendall's W value of 1.000 for total coliform indicated that the ordering of the sampling periods was identical across all four years. NDWI was not significantly associated with any of the examined water-quality parameters. For NDTI, only its relationship with electrical conductivity remained significant in both Pearson (r=0.7649, adjusted p=0.0056) and Spearman (ρ=0.7432, adjusted p=0.0097) analyses. However, because electrical conductivity is not a directly optically active parameter and the relationship was based on only 16 observations, this finding was not interpreted as a predictive model. The results indicate that NDWI and NDTI cannot replace laboratory analyses but may serve as complementary monitoring tools when supported by more extensive field observations and independent validation data.

Keywords

• Dicle Dam
• water qualıty
• Sentinel-2A
• NDWI
• NDTI
• temporal variation

Ethical Statement

This study did not involve human participants, animals, or any experimental procedures requiring ethical committee approval. Water samples were collected from the Dicle Dam intake structure as part of routine environmental monitoring, and no interventions affecting humans, animals, or protected ecosystems were performed. The authors declare that the study was conducted in accordance with the principles of research integrity and publication ethics.

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