Abraha Adugna Ashenafi

The Large Zarima-Mayday dam Reservoir Project, situated in the Tekeze River Basin in Northern Ethiopia, represents a critical water infrastructure initiative designed to support large-scale agricultural expansion specifically sugarcane cultivation and supply downstream environmental flows. Despite its total impoundment capacity of 3.6 BCM, steep valley morphology limits active usable storage to 785 MCM. However, a major strategic flaw in the project’s execution is the failure to implement standard design protocols that integrate reservoir filling in parallel with phased dam construction. Consequently, civil works reached full completion without initiating impoundment, transforming a multi-million-dollar asset into an idle structure facing a four-year filling bottleneck and severe capital lockup. This study evaluates post-construction reservoir operational policies and water supply reliability using the HEC-ResSim model across a 51-years historical hydrologic dataset (1968–2018). Simulation results reveal that under full land development (40,000 ha), the reservoir suffers severe irrigation water deficits in 51% of simulated months. Scaled development scenarios of 30,000 ha and 25,000 ha reduce monthly deficit frequencies to 15% and 11%, respectively. To mitigate such delays in future megaprojects and ensure operational sustainability, integrating dynamic rule curves, phasing impoundment concurrently with civil construction, and adopting high-efficiency micro-irrigation systems are strongly recommended.

Large-scale water infrastructure across the East African Rift System faces severe structural degradation and capacity underutilization driven by coupled hydro-geotechnical failures. This study presents a forensic engineering investigation into post-construction left-rim reservoir seepage bypass, rock-slope instabilities, and spillway design and construction deficits at the multi-purpose Gerebsegen Dam in northern Ethiopia, positioning the findings within the macro-regional discourse on East African dam safety paradigms. Engineered with a 30-year design period to provide municipal water to Mekelle city and irrigation purposes, the project exhibits a critical discrepancy between chronological age and operational efficiency. Although 12 years have elapsed since construction, the reservoir utilizes only 20% of its design storage volume. This deficit has neutralized two of the system’s three pressure conduit outlets, completely abandoning the 500-hectare irrigation supply and a secondary 250 lit/sec municipal line. Consequently, operational yield is restricted to the primary municipal pipe, which delivers only 150 lit/sec due to severe pump downtime despite a 250 lit/sec design capacity. To isolate the root failure causes, geotechnical site characterization and a hydrogeological mass-balance model were deployed. Geotechnical investigations using core drilling and Electrical Resistivity Tomography (ERT) revealed that the reservoir’s left abutment rim is heavily fractured by tectonic joint networks and cross-cut by highly permeable, weathered dolerite intrusions. This deficient geological boundary condition permitted high hydraulic gradients to drive a massive lateral subsurface short-circuiting seepage bypass of 568 lit/sec out of the storage basin. Crucially, this structural bypass is continually masked by a perennial upstream river baseflow contribution of 372 lit/sec, resulting in a net observed reservoir drawdown rate of approximately 373 lit/sec. Furthermore, kinematic slope stability assessments identified severe structural vulnerabilities along the reservoir rim and spillway chute channels, where excavated rock slopes are cut at unstable, near-vertical angles of 75° to 80°, and triggering block failures. Hydraulic reassessments also confirmed that the existing spillway is significantly under-poor construction, failing safely to pass extreme peak flood discharges. These findings establish a vital diagnostic workflow and highlight the necessity of coupling rock-mass slope forensics with hydrogeological mass-balance modeling to design resilient abutment cutoff systems in fractured rifts. To mitigate these structural risks, a regional-standard remedial engineering package is evaluated, featuring a structural replacement with a rigid, tapered cantilever reinforced concrete structure up to 7.20 m high, a 1,700.50 m³ upper-slope offloading excavation to a stable 45° profile, and a subsurface pressure-grouting curtain.

This study presents an integrated engineering assessment of the Gerusernay embankment dam located in Adihforom Woreda, Tigray Region, northern Ethiopia, a water-scarce area characterized by high rainfall variability and recurrent drought. The assessment focuses on hydrological adequacy, seepage behavior, engineering geological conditions, and construction performance to evaluate the dam’s functionality and safety under site-specific conditions. The methodology combines field observations, water balance analysis, and seepage evaluation to examine system performance in an ungauged catchment context.The results indicate that overall seepage remains within acceptable design limits; however, localized seepage losses associated with unfavorable geological conditions and construction deficiencies were identified. Hydrological analysis reveals that limited and variable inflow significantly constrains reservoir performance, highlighting the critical role of catchment diversion in augmenting water availability and reducing hydrological uncertainty. In addition, gaps in construction quality, including incomplete implementation of design provisions and inadequate material control, were found to adversely affect system efficiency and reliability.The findings underscore the importance of integrated hydrological and geotechnical assessment, improved site investigation, and strict construction supervision to ensure the long-term performance of embankment dams in semi-arid environments. The study provides practical insights for enhancing the design, construction, and management of water storage infrastructure in Tigray and similar water-stressed regions.

This paper aims to quantify the subbasin’s potable water supply demand forecast from 2023 to 2050 under various scenarios of climate change and socioeconomic development. The variability of the climate and the resulting problems with urbanization threaten the availability of water resources, especially in less developed countries like Ethiopia. Thus, the main objective of this study is showing the necessary to determine the amount of water needed in advance, in order to comply with the availability of water resources within a specified future period under different scenarios. Our indicator-based approach used a multicriteria decision-making technique. Accordingly, several important variables were considered, including climatological, anthropological, demographic, socioeconomic, and economic variables, in addition to water engineering-related factors (e.g. Water losses). The method also considered a number of factors, such as unexpected and extreme temperature changes, and forecasting factors studied by the Ethiopian Ministry of Water and Energy. The projected population in the subbasin is estimated at 2.52 million, so the total projected water supply demand i.e., for domestic, non-domestic, industrial, commercial, public, and institutional is approximately 126.53 MCM/yr by 2050. Our results revealed how changes in both climatic and socioeconomic factors strongly influence future water resource system performance, and this will help the water services provider better prioritize the refurbishment of existing infrastructure and investment in new infrastructure, and more importantly, manage the subbasin effectively by introducing resilient adaptation options.

The impact of climate change on water resources is a global issue with significant regional implications. The Ghba subbasin has experienced a higher socioeconomic change. In this paper, we assess the potential impact of climate change and human activity on water supply and demand in the Ghba subbasin of Ethiopia. We then evaluate the effectiveness of regional adaptation strategies for water supply management under these conditions. To do this, we use the statistical downscaling model (SDSM) and the water assessment and planning tool (WEAP) to simulate and analyse future water conditions. After running the model through a calibration and validation process, minimum (Tmin) and maximum (Tmax) temperatures, water demand and unmet water demand were projected for 2100 horizon, using different climate change scenarios. The results showed that the model's performance, calibration, and validation were all satisfactory. The analysis showed that, under A2 and B2 emission scenarios of the Intergovernmental Panel on Climate Change (IPCC), the mean precipitation will increase by 31% and 26%, respectively. The projected mean Tmax and Tmin will be warmer than the baseline period, with Tmax increasing by 1.5°C (A2) and 1.3°C (B2), and Tmin by 1.7°C (A2) and 1.5°C (B2) by 2100. The results also illustrate that in all scenarios, water consumption would rise and that this need will not be satisfied, and the pressure on water resources will intensify, resulting in a water shortage. The findings show that future water demand under the influence of climate change is projected to exceed 210 million cubic meters (MCM) by 2100. The findings show that while the evaluations of the recommended adaption techniques are effective, they are not enough to guarantee the Ghba subbasin's water sustainability.

Water resource evaluation, management, and conservation at the local, national, and international levels depend on an accurate understanding of the hydrological processes. In data-poor environments and topographically complicated areas like the Ghba subbasin in the headwaters of the Nile River, the function of hydrological models is crucial. The primary goal of this study is to use the WEAP model to simulate the hydrology of the Ghba basin. This is because recent hydrological behaviour has changed significantly and resulted in a serious water deficit. The minimal satisfactory performance limit for the monthly stream flow variable was strongly attained by the multi-variable calibration scenario (R2 = 0.82, NSE = 0.82, IA= 0.80 RSR = 0.87 and PBIAS = 9 % for calibration scenario; and R2 = 0.78, NSE = 0.81, IA= 0.70 RSR = 0.80 and PBIAS = 11.5 % for validation scenario). Evapotranspiration makes up 63.4% of the water balance, according to the model simulation, while surface runoff, interflow, baseflow and groundwater recharge accounting for 11.1 %, 11.8%, 5.4% and 8.3 %, respectively. The simulated average annual streamflow at the subbasin outlet is 16.33 m3/s. The simulated monthly minimum flow occurs in January with an average flow of 1.78 m3/s and a coefficient of dispersion of 0.45. Maximum flows occur in July and August, with an average flow of 53.57 m3/s and a coefficient of dispersion of 0.19. The main rainy season was shown to have a larger spatial distribution of simulated runoff, and the average annual recharge value is 53.5 mm. The study's conclusions indicated that both surface water harvesting and groundwater extraction might be used for reliable water distribution to the subbasin's continuously increasing sectoral water demand.