River Nile 3rd reach: monitoring post-Aswan Dam riverbed morphological changes in Egypt

Abstract

This study investigates riverbed morphological changes along the River Nile 3rd reach (R3) downstream of Naga-Hammadi barrages following the High Aswan Dam (HAD) construction. The background highlights how large dams like HAD have altered global river systems, leading to sediment trapping and downstream erosion issues. The primary issue addressed is the lack of detailed spatial and temporal analysis of these changes in the Nile, impacting irrigation, navigation, and ecosystem stability. The goal is to provide a comprehensive assessment using long-term data. Using daily discharge and water surface level records (1962–2010) from eight gauge stations, annual stage-discharge rating curves were developed to quantify water level and bed changes at a reference discharge of 180 million m3/day. Results reveal significant upstream degradation, with water surface levels dropping by up to 0.99 m, while downstream segments experienced aggradation, reaching an 88.9 cm rise at El-Khazendaria in 2000. The longitudinal slope declined from 7.00 cm/km (1962–1963) to 6.49 cm/km (2009–2010). Notably, 2000–2010 experienced an unusual water level decline across the reach, peaking at 68.9 cm at El-Maragha. These findings highlight HAD’s complex, spatially variable impacts and subsequent interventions on Nile riverbed stability. The two-dimensional numerical model (SMS) was used to compare the morphological changes between 1982 and 2003 and to corroborate and validate the study findings. Implications include improved sediment management and infrastructure design for sustainable river use. Future research should integrate climate models to predict changes under global warming scenarios.