Sediment Assessment Using Coupled RUSLE-SDR Models of Future Mellegue2 Dam in Tunisia

Abstract

Over the last 60 years, Mellegue1 Dam has lost approximately 80% of its original 268 million cubic meter capacity to siltation, reflecting broader Mediterranean basin patterns in which climate-driven erosion has exacerbated dam sedimentation rates. In response, the strategic building of the upstream Mellegue2 Dam is intended to address water scarcity, improve flood management, and ensure a continuous supply of water for agricultural and domestic purposes. This study fills critical knowledge gaps by integrating climate change projections with sediment modeling in Mediterranean semi-arid environments, developing spatially explicit conservation strategies using combined RUSLE-SDR and SWAT modeling, and evaluating management interventions under future scenarios using drought-flush erosion mechanisms documented across the Mediterranean basin. This study evaluates sediment dynamics in the Mellegue2 Dam watershed from 1993 to 2019 using an integrated RUSLE-IC-SDR modelling approach, with model validation performed using a three-tiered framework that included SWAT comparison, historical sedimentation records, and regional correlation analysis. The model performed well (NSE=0.78, R²=0.82), with an average annual prediction error of 12.3%, similar to verified Mediterranean erosion models. Monte Carlo simulation with 1000 iterations, accounting for parameter variability in R-factor (±15%), K-factor (±20%), and C-factor (±25%), yielded confidence intervals of -18% to +22% for annual forecasts. The temporal study demonstrates drought-flush erosion mechanisms common to Mediterranean climates, with post-drought sediment outputs increasing by 40-60% above normal years, consistent with regional research from Spain, Italy, and Greece. According to the management scenario study, Mellegue2 Dam will lose 50% of its capacity within 24 years if no intervention is implemented. However, comprehensive watershed management based on proven Mediterranean basin conservation practices has the potential to increase operational lifespan to 75 years while also delivering broader environmental benefits. The study finds three priority management zones that require distinct conservation approaches, with the largest return on investment found on northwestern slopes with erosion rates of more than 12 t/ha/year. These findings contribute to better knowledge of climate-driven erosion processes across the Mediterranean and offer management solutions that can be applied to similar semi-arid watersheds.

Keywords

• Sediment Export
• Soil Erosion
• RUSLE
• SDR
• SWAT
• Index of Connectivity
• Watershed Management
• Tunisia

Supporting Institution

This research was supported by the research project "Management of the phenomenon of silting and mapping of the risk of erosion of the watersheds of the large dams of the upper valley of Medjerda," awarded within the framework of the Program of Encouragement of Young Researchers (PEJC), Project No. PEJC20-2017, under the Ministry of Higher Education and Scientific Research of Tunisia.

Project Number

PEJC20-2017

Ethical Statement

This study did not involve human participants, animals, or sensitive data, and therefore did not require ethics committee approval

Thanks

We would like to express our sincere gratitude to Mr. Belgacem Jarray, Principal Engineer in the Directorate of Dams and Big Hydraulic Works for data providing.

Tunus'ta Gelecekteki Mellegue2 Barajının Birleştirilmiş RUSLE-SDR Modelleri Kullanılarak Sediman Değerlendirmesi

Abstract

Son 60 yılda, Mellegue1 Barajı, iklim kaynaklı erozyonun baraj sedimantasyon oranlarını artırdığı Akdeniz havzasındaki genel eğilimi yansıtarak, orijinal 268 milyon metreküp kapasitesinin yaklaşık %80'ini siltasyon nedeniyle kaybetmiştir. Buna yanıt olarak, yukarı akışta stratejik olarak inşa edilen Mellegue2 Barajı, su kıtlığını gidermeyi, sel yönetimini iyileştirmeyi ve tarımsal ve evsel amaçlar için sürekli su teminini sağlamayı amaçlamaktadır. Bu çalışma, iklim değişikliği tahminlerini Akdeniz yarı kurak ortamlarındaki sediman modellemesiyle entegre ederek, RUSLE-SDR ve SWAT modellemesini birleştirerek mekansal olarak açık koruma stratejileri geliştirerek ve Akdeniz havzasında belgelenen kuraklık-akış erozyon mekanizmalarını kullanarak gelecek senaryoları altında yönetim müdahalelerini değerlendirerek kritik bilgi boşluklarını doldurmaktadır. Bu çalışma, entegre RUSLE-IC-SDR modelleme yaklaşımı kullanılarak 1993'ten 2019'a kadar Mellegue2 Barajı havzasındaki sediman dinamiklerini değerlendirmekte ve model doğrulaması SWAT karşılaştırması, tarihsel sedimantasyon kayıtları ve bölgesel korelasyon analizini içeren üç aşamalı bir çerçeve kullanılarak gerçekleştirilmektedir. Model, doğrulanmış Akdeniz erozyon modellerine benzer şekilde, ortalama yıllık tahmin hatası %12,3 ile iyi bir performans göstermiştir (NSE=0,78, R²=0,82). R faktörü (±%15), K faktörü (±%20) ve C faktörü (±%25) parametre değişkenliğini hesaba katan 1000 yinelemeli Monte Carlo simülasyonu, yıllık tahminler için %-18 ile %+22 arasında güven aralıkları vermiştir. Zamansal çalışma, Akdeniz iklimlerinde yaygın olan kuraklık-sel erozyonu mekanizmalarını göstermektedir. Kuraklık sonrası sediment çıkışı normal yıllara göre %40-60 oranında artmaktadır. Bu sonuç, İspanya, İtalya ve Yunanistan'da yapılan bölgesel araştırmalarla tutarlıdır. Yönetim senaryosu çalışmasına göre, Mellegue2 Barajı, herhangi bir müdahale yapılmazsa 24 yıl içinde kapasitesinin %50'sini kaybedecektir. Ancak, Akdeniz havzasında kanıtlanmış koruma uygulamalarına dayanan kapsamlı havza yönetimi, operasyonel ömrü 75 yıla çıkarırken, daha geniş çevresel faydalar da sağlayabilir. Çalışma, farklı koruma yaklaşımları gerektiren üç öncelikli yönetim bölgesi belirlemektedir. En yüksek yatırım getirisi, erozyon oranının 12 t/ha/yıl'ın üzerinde olduğu kuzeybatı yamaçlarda görülmektedir. Bu bulgular, Akdeniz'deki iklim kaynaklı erozyon süreçleri hakkında daha iyi bilgi edinilmesine katkıda bulunmakta ve benzer yarı kurak havzalara uygulanabilecek yönetim çözümleri sunmaktadır.

Keywords

• Sediment İhracı
• Toprak Erozyonu
• RUSLE
• SDR
• SWAT
• Bağlantılılık İndeksi
• Havza Yönetimi
• Tunus

Project Number

PEJC20-2017

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