A Geophysical Approach to Post-Construction Integrity Assessment of Earth Dam Embankment, Case Study of Ero Dam, Ikun- Ekiti Southwest Nigeria

Co-Authors

Ademilua O. L., Eluwole A.B., Talabi A. O.

Citation

Ademilua Oladimeji Lawrence, A Geophysical Approach to Post-Construction Integrity Assessment of Earth Dam Embankment, Case Study of Ero Dam, Ikun- Ekiti Southwest Nigeria(2016)SDRP Journal of Earth Sciences & Environmental Studies 1(3)

Abstract

Dams and reservoirs are a dynamic slice of our national infrastructure and provide power, water, recreation, irrigation, flood protection, and many other advantages to growing populations across Nigeria. Assessing the integrity of these structures is a critical component of sustained operations. Post-Construction Integrity Assessment of Ero Dam at Ikun- Ekiti Southwest Nigeria was undertaken employing spontaneous potential (SP) and electrical resistivity surveys (VES and Dipole – Dipole) with a view to delineate the subsurface geoelectric sequence/parameters and identify structures such as faults and fractured zones, network of joints, seepages and basement depressions that are threats to the existence of the dam. SP survey revealed that the seepage zones were found within stations 2-4 inbetween distance 10-20m and stations 7-10 within 35-50m on the ground. The calculated SP depths for stations 2 – 4 and 7 – 10 were 5m and 6m respectively. The SP survey indicated the peak negative profile of the streaming potential which is a pointer to an area where there is possibility of seepage in the dam embankment. VES survey revealed that VES 1 depicted HK curve type while both VES 2 and 3 were characterized as H curve. There is marked variation in resistivity with depth across the study area with values that ranged from 37 - 251?m. Areas of lower resistivity are due to an increase in pore water content as revealed in the various resistivity values of the sounding locations. The seepage zone has low resistivity value and constitutes a point of weakness in the dam which can result in flooding of the embankment. Dipole – Dipole assessment of the Dam revealed that the first layer in the subsurface configuration of Ero Dam is laterite (? ranged from 100?m to 230?m). The second layer (leaky part of the dam core) is clay with apparent resistivity values ranging between 45?m and 85?m. The resistivity value between 105?m and 213 ?m approximately represents the intact dam core (weathered rock) which is the third layer characterizing competent zone. The moderately low resistivity layers are zones of interest in terms of post construction integrity assessment of a dam. The dam’s core is made up of clay indicating seepage problem. In view of the SP values and results of VES and Dipole – Dipole surveys, Ero Dam suffers seepage problem and needs rehabilitation and constant maintenance.

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