Abstract
Saline water intrusion presently constitutes serious concerns in the Lagos municipality just like many other coastal cities, thus necessitating its intervallic study. The present study involving 52 borehole logs (consisting of natural gamma and electrical resistivity components) was aimed at delineating intruded and vulnerable zones. Saline water columns defined by low resistivity values in the range of 0.1 and 20 Ωm as compared to fresh water (≥ 100 Ωm) were delineated on 22 logs. Four of the geosections generated in this study indicate saline water intrusion at depths varying from surface in Satellite Town, Kirikiri, Ijora, Iganmu, Apapa, Lagos Island, Ikoyi, Victoria Island and Lekki to depths ranging from 40 m at Iganmu to 158 m at Lekki. Intrusions of 47 m (143 - 190 m) and 60 m (56 - 116 m) were delineated at Ajah; 50 m (265 - 315 and 258 - 308) at Lakowe; 57 and 112 m (51 - 108 m and 198 308) at Ibeju Lekki, Akodo and 122 m at (233 - 355m) at Awoyaya. The hydrogeologic importance of the Coastal Plain Sand aquifer unit in Lagos is under severe threat of continued sea water intrusion on its southern flank. This study illustrates the current extension of the sea water intrusion. It highlights the depreciation of the water resource due to over pumping at higher rate than the natural recharge and slow sea level rise.
Highlights
Seawater intrusion is an inevitable problem of coastal fresh water aquifer associated with urban area (Hwang et al, 2004)
There is vital need to monitor the feasible risk of saline water intrusion of the coastal aquifers because, once saline intrusion into coastal aquifer has occurred, it is extremely difficult to overcome and improve the management of the water resources based on long term strategy
The challenge of saline water contamination in coastal aquifers is driven by a violation of the delicate hydrogeological balance that exists between freshwater and seawater in coastal aquifers (Goldman and Kafri, 2004) due to large-scale groundwater abstraction occasioned by rapid urbanization (Pareek et al, 2006)
Summary
Seawater intrusion is an inevitable problem of coastal fresh water aquifer associated with urban area (Hwang et al, 2004). Coastal aquifers constitute a vital source of fresh water in these regions, and are increasingly used to meet the water supply needs (Pareek et al, 2006). There is vital need to monitor the feasible risk of saline water intrusion of the coastal aquifers because, once saline intrusion into coastal aquifer has occurred, it is extremely difficult to overcome and improve the management of the water resources based on long term strategy. The challenge of saline water contamination in coastal aquifers is driven by a violation of the delicate hydrogeological balance that exists between freshwater and seawater in coastal aquifers (Goldman and Kafri, 2004) due to large-scale groundwater abstraction occasioned by rapid urbanization (Pareek et al, 2006)
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