Flood Dynamics and Floodplain Alterations Over Two Decades: A Hydrogeomorphological Study of the Larbaâ River, Northern Morocco

¹ Faculty of Sciences Dhar El Mahrez, Sidi Mohamed Ben Abdellah University, Fes, Morocco,
² Faculty of Human and Social Sciences, Ibn Tofail University, Morocco,
³ Higher Institute of Nursing Professions and Health Techniques of Fez (Annex Taza), Morocco,
⁴ Faculty of Sciences and Techniques, Sidi Mohamed Ben Abdellah University, Fes, Morocco.

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Proactive tracking of flood dynamics is essential for identifying floodplain alterations, anticipating newly vulnerable areas, and ultimately updating flood hazard maps. This study inspected changes along the Larbaâ River pathway in Taza City using the hydrogeomorphological method over a two-decade period (2006-2025). We commenced by elaborating initial flood maps based on aerial photographs from 1982 and recent satellite images from 2025. We then relied on observational insights from field campaigns in 2006 and 2025 to identify changes in natural riverland. We supplemented the initial maps with on-site evidence, including sedimentary deposits, flood marks on structures and vegetation, and eyewitness reports from community members. The results showed that floodplain sections are divided into three riverbeds (the minor bed, middle bed, and major bed), arranging them according to a hierarchy of flood risk categories: high, moderate, and low. Certain floodplain sections near the Al Malha neighborhood are significantly modified through embankment construction and urban encroachment, altering natural landforms and consequently reinforcing flood effects. Field investigations revealed that human activities have intensified flooding impacts more than natural factors. Historical analysis and eyewitness data enriched understanding of extreme flood magnitude. Our flood risk maps represent flood limits, from non-overflowing events to exceptional incidents. The maps do not explicitly depict future flooding; rather, they highlight areas that have experienced inundation in the past. While effective for tracking historical flood zones, the method encounters limitations in heavily modified urban sections, suggesting the need for integrated approaches combining geomorphological analysis with hydrodynamic modelling