EVALUATION AND OPTIMISATION OF SITING OF SMALL DAMS AND RESERVOIRS IN NORTHERN GHANA

Abstract

Water shortage is a significant challenge in developing countries, particularly in semi-arid and arid regions, posing obstacles to irrigation and human survival. Northern Ghana experiences a rainy season with occasional floods, water shortages, and dry spells. To address this recurring issue, a study on optimization of small dams and reservoirs was necessary. This study focused on sixteen (16) selected sub-catchments in three (3) northern Ghana regions where small dams and reservoirs were developed for domestic and agricultural purposes. On-site investigation of current status of reservoirs, engineering and structural conditions were conducted. Hydraulic conductivity and soils of embankment were analysed. Upstream simulation of spatio-temporal land use/landcover dynamics impacts on runoff generation was analysed using geographic information system, remote sensing techniques and curve number model. Additionally, the suitability assessment of the constructed small dams and reservoir locations was conducted using an analytic hierarchy process. Scenarios of optimal storage capacity of suitable dam locations were determined using 2D and Civil 3D. The results of the study highlighted the multifaceted challenges associated with small dam failures, emphasizing the need for a holistic approach that integrates engineering solutions and improved design. The comprehensive assessment highlighted variability in hydraulic conductivity ranging from 0.742 × 10-6 to 12.7 ×10-6 cm/s indicating lower and higher permeability and potential seepage, respectively. Spatial-temporal analysis of landuse and landcover from 1995 to 2023 revealed upstream anthropogenic activities, such as the conversion of grassland to agricultural/arable lands and built-up areas, indicating historical landuse and landcover changes and their impact on hydrological mechanisms, and the increase in impervious surfaces resulting in enhanced surface runoff. Findings on suitability assessment of the small dam locations revealed that ten (10) of the dams were located away but less than 100 m from major streamflow networks, posing potential challenges in optimal surface runoff collection. An overall analysis of suitable locations of dams and their optimal storage capacity identified potential relocations for six (6) dams. The proposed new dam locations and their storage capacities were deemed crucial for addressing water scarcity while balancing conflicting needs of various water users. The study findings underscored the significance of research-based decision-making in addressing water shortages and maintaining a balance between agricultural, domestic, and environmental water needs. Regular inspection programmes are recommended to identify and address problems early, preventing complex and costly issues. Assessment of challenges and opportunities in water infrastructure development under changing climatic conditions, and evaluation of socioeconomic impacts and involving communities for sustainability and resilience of small dams were suggested for future research.