A Bi-level Neuro-Fuzzy System Soft Computing for Reservoir Operation

Reservoir operation studies purely based on the storage level, inflow, and release decisions during dry periods only fail to serve the optimal reservoir operation policy design because of the fact that the release decision during this period is highly dependent on wet season water conservation and flood risk management operations. Imperatively, the operation logic in the two seasons are quite different. If the two operations are not sufficiently coordinated, they may produce poor responses to the system dynamics. There are high levels of uncertainties on the model parameters, values and how they are logically operated by human or automated systems. Soft computing methods represent the system as an artificial neural network (ANN) in which the input- output relations take the form of fuzzy numbers, fuzzy arithmetic and fuzzy logic (FL). Neuro-Fuzzy System (NFS) soft computing combine the approaches of FL and ANN for single purpose reservoir operation. Thus, this study proposes a Bi-Level Neuro-Fuzzy System (BL-NFS) soft computing methodology for short and long term operation policies for a newly inaugurated irrigation project in Gidabo Watershed of Main Ethiopian Rift Valley Basin. Keywords: Bankruptcy rule, BL-NFS, Reservoir operation, Sensitivity analysis, Soft computing, Water conservation.

Main Ethiopian Rift landslides formed in contrasting geological settings and climatic conditions

The Main Ethiopian Rift (MER), where active continental rifting creates specific conditions for landslide formation, provides a prospective area to study the influence of tectonics, lithology, geomorphology, and climate on landslide formation. New structural and morphotectonic data from central Main Ethiopian Rift (CMER) and southern Main Ethiopian Rift (SMER) support a model of progressive change in the regional extension from NW–SE to the recent E(ENE)–W(WSW) direction, driven by the African and Somali plates moving apart with the presumed contribution of the NNE(NE)–SSW(SW) extension controlled by the Arabian Plate. The formation and polyphase reactivation of faults in the changing regional stress field significantly increase the rocks' tectonic anisotropy, slope, and the risk of slope instabilities forming. According to geostatistical analysis, areas prone to landslides in the central and southern MER occur on steep slopes, almost exclusively formed on active normal fault escarpments. Landslide areas are also influenced by higher annual precipitation, precipitation seasonality, vegetation density, and seasonality. Deforestation is also an important predisposition because rockfalls and landslide areas typically occur on areas with bushland, grassland, and cultivated land cover. A detailed study on active rift escarpment in the Arba Minch area revealed similar affinities as in a regional study of MER. Landslides here are closely associated with steep, mostly faulted, slopes and a higher density of vegetation. Active faulting forming steep slopes is the main predisposition for landslide formation here, and the main triggers are seismicity and seasonal precipitation. The Mejo area situated on the uplifting Ethiopian Plateau 60 km east of the Great Rift Valley shows that landslide occurrence is strongly influenced by steep erosional slopes and a deeply weathered Proterozoic metamorphic basement. Regional uplift, accompanied by rapid headward erosion forming steep slopes together with unfavourable lithological conditions, is the main predisposition for landslide formation; the main triggers here are intense precipitation and higher precipitation seasonality.

Catching the Main Ethiopian Rift evolving towards plate divergence

Magmatism accompanies rifting along divergent plate boundaries, although its role before continental breakup remains poorly understood. For example, the magma-assisted Northern Main Ethiopian Rift (NMER) lacks current volcanism and clear tectono-magmatic relationships with its contiguous rift portions. Here we define its magmatic behaviour, identifying the most recent eruptive fissures (EF) whose aphyric basalts have a higher Ti content than those of older monogenetic scoria cones (MSC), which are porphyritic and plagioclase-dominated. Despite these differences, calculations highlight a similar parental melt for EF and MSC products, suggesting only a different evolutionary history after melt generation. While MSC magmas underwent a further step of storage at intermediate crustal levels, EF magmas rose directly from the base of the crust without contamination, even below older polygenetic volcanoes, suggesting rapid propagation of transcrustal dikes across solidified magma chambers. Whether this recent condition in the NMER is stable or transient, it indicates a transition from central polygenetic to linear fissure volcanism, indicative of increased tensile conditions and volcanism directly fed from the base of the crust, suggesting transition towards mature rifting.