Environmental impact assessment: Geologic tool to investigate the proposed Enji dam construction, Offa, Kwara state

Abstract

The proposed dam axis geographical locations are on Latitude N080 39' 38.5 '', longitude E040 46' 28.6'' and latitude N080 39' 26.9'', longitude E04° 46' 33.3'' and its axis traverses various communities like Enji (40 rooms), Gbomi, Fatraj (Ile mojedun), Atooba (Ariya), St. Claire's junction (Ikotun road), Keraaje site.Detailed laboratory analyses of air, noise, water and soil pollutants using collected samples of the area gave reliable baseline data.Geotechnical report of the area revealed basic information of the area.More importantly, questionnaires were designed and administered to assess positive and adverse impacts.Results obtained revealed the proposed area for the construction of a dam will be feasible to impound water for storage with catchment area of 38 km2 envisaged, annual runoff has been estimated to be about 52,988,620 m 3 .The freeboard is assessed to be 2 meters.Crest length and elevation are 106.9m and 45 a.s.l.(above sea level) respectively.Spillway type and discharge rate were considered to be broad crested and 377 m 3 s -1 respectively.But adverse impacts will be recorded and include among others silting of the dam, risk of eutrophication/growth of non-native and/or invasive species, growth of aquatic macrophytes in the littoral and sub-littoral zone of the proposed reservoir, creation of favorable habitats for the growth and proliferation of disease vectors, risk of introduction of new diseases like schistosomiasis, bilharzias.With more positive impacts than the adverse effects, the study concluded that the project is feasible and will contribute to economic prosperity of the area.