Life cycle assessment of options for retrofitting an existing dam to generate hydro-electricity

Abstract

Existing dams in Nigeria have in recent times been considered for retrofit to generate hydroelectricity to meet the energy needs of its growing population. While the environmental impacts of such developments remain uncertain, this study was done to ascertain the potential environmental impacts of three possible options for retrofitting an existing dam to generate hydroelectricity. The options include modification of the embankment or one spillway bay or one scour radial gate. The life cycle assessment (LCA) of the case study encompassed the cradle-to-grave aspect of the ISO 14040 guidelines. The functional unit adopted is defined as 1 MWh of net electricity produced. The CML 2001 methodology was adopted to characterize environmental impacts. The impact categories considered in this study include global warming potential (GWP), abiotic depletion potential fossil (ADPf), acidification potential (AP), human toxicity potential (HTP), freshwater aquatic ecotoxicity potential (FAETP), eutrophication potential (EP), ozone layer depletion (ODP), photochemical ozone creation potential (POCP), terrestrial ecotoxicity potential (TETP) and abiotic depletion potential elements (ADPe). Sensitivity analysis was also done to identify key contributors to impact category for the entire life cycle of the plant, so as to suggest better environmental performance strategies. Findings from this study have shown that for all possible options, the construction stage is the major contributor to environmental impacts, accounting for over 90% of impacts for the entire life cycle of the project. Steel is the dominating of all three options in terms of material input. A thorough look at the construction cost implications, advantages and disadvantages of the three options have shown that the embankment option, which is the most expensive in terms of material and energy, turns out to be the best available option due to its potential to avoid graver risk during operation. Results of sensitivity analysis have also shown that optimization of all potential options is a more cost-effective way to generate electricity while minimizing substantial environmental impacts. Similar to majority of engineering projects, the construction stage of hydropower projects is the major contributor to environmental impacts. To mitigate such impacts, strategic planning, new materials and manufacturing techniques to improve the performance and lower the costs are highly suggested. Additionally, as much as costing plays a critical role in determining the executability of hydropower projects, potential risks associated with retrofitting dams must not be taken lightly.