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Sustainability of a hydraulic facility and flood risk of its downstream section: the case of the Foum El-Gherza dam (Ziban east, Algeria)

Zakarya Maou, Bougherara Ahmed, Habibi Yahyaoui

Geomatics, Landmanagement and Landscape

2023

no. 2

7--22

Due to advanced silting, the Foum El-Gherza dam has lost more than two thirds of its initial capacity (47 hm3) and is no longer able to withstand the floods that threaten its downstream section. Indeed, the damage recorded in recent years has confirmed the vulnerability of the man-made structures located on both banks of the Oued Labiod. Thus, we believe that the hydrological behaviour of the catchment area is no longer influenced by the dam. Therefore, the hydrological study involved a critical analysis (homogeneity tests) of the hydro-climatic data in order to highlight the characteristics of the historical events recorded during the period 1950–2019. The frequency study of the maximum daily rainfall and floods recorded at the dam allowed us to determine the rainfall and flow rates of the return periods (10, 25, 50, 100, 500 and 1000 years). The flooding of the 28 October 2011 were used as a standard for the calibration of the model calculated by the HEC-Ras software. After validation of the model, a prediction of the water levels and flood extent was made for the selected return periods. The results obtained show that a part of the town of Seryana (district located on the edge of the right bank) suffers from flooding proportionally to the return periods of the floods. In addition, some agricultural areas bordering the Oued are also affected by the floodings. The hazard modelling maps can be considered as a basis for a flood risk prevention plan (PPRI) and as a decision support tool.

Assessment of relative-active tectonics in rhumel-smendou basin (ne Algeria) – observations from the morphometric indices and hydrographic features obtained by the digital elevation model

Manchar Nabil, Hadji Riheb, Bougherara Ahmed, Boufaa Kamel

Geomatics, Landmanagement and Landscape

2022

no. 4

47--65

The eastern Tell Atlas of Algeria is characterized by a complex neotectonic system including lateral strike-slips, and normal and reverse faults. The landscape of the Neogene basin of MilaConstantine acquired its shape due to the perpetual action of tectonic activity, and erosion processes. Neo-tectonics in this basin have affected the geometry of the stream network and the contemporary landscape topography. Our methodology evaluates the active tectonics in this mountainous region by a combination of drainage network and geomorphic indices, namely, the basin-shape index (Bs), stream-length gradient (SL), hypsometric integral (HI), mountain front sinuosity (Smf), basin asymmetry factor (AF), and valley-floor ratio (Vf). The calculated values of the six measured geomorphic indices were used to differentiate the distribution of faults function as well as the relative tectonic activity in the study area. The obtained results from the GIS-based multi-criteria analysis of these indices consist of the index of active tectonics (IAT). Hence, we defined four hierarchic degrees of IAT, namely, very high (VH), high (H), moderate (M), and low (L). The relative active tectonics represents an obvious correlation between morpho-structural features, tectonic activities, and uplift rates. It selects the morphotectonic features and landforms that interpret the tectonic events in the study area. Our results prove that this approach discerns the most active regions related to the neo-tectonic action in the RhumelSmendou drainage basin. The combination of geomatics and field surveys highlights the cliffs which are still rising by using the drainage patterns, the landform model, and the mountain range shape.