Constrained Time‐Lapse Resistivity Imaging Inversion

We investigated the internal structure of the Lotsane Dam for zones that may be prone to seepage and internal erosion using the electrical resistivity imaging (ERI) and the frequency domain electromagnetic (FDEM) methods. Time-lapse ERI measurements were also made for a period of 8 months in order to monitor the temporal evolution of defective zones. Results from both the FDEM and ERI measurements show two main layers. The first is an upper conductive layer varying in thickness from 10 to 25 m which is related to the clay core embankment. Situated beneath this upper conductive layer is a highly resistive crystalline basement on which the dam was founded. Furthermore, the ERI and FDEM measurements revealed the presence of fractures and possible zones of weakness within the dam foundation. Time-lapse ERI measurements revealed resistivity increases in the observed possible defective zones, including proximal to the spillway and at the embankment-foundation interface. The long-term resistivity variation may be indicating change in material properties in those portions of the dam, and may evolve to destabilize the structural integrity of the dam and or develop into preferential seepage pathways with time. The identified anomalous zones are good indicators that the embankment integrity is at risk and we suggest continuous geophysical monitoring of Lotsane Dam structure in order to ensure dam safety and integrity on the long term.

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Studying Effect of Riverbank Filtration (RBF) on Ground Water Using ‘Time-Lapse Electrical Resistivity Imaging’ at Kuala Kangsar, Perak

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.802.605 ◽

2015 ◽

Vol 802 ◽

pp. 605-610

Author(s):

Mohd Hanis Mohamad ◽

Mohd Nawawi ◽

Mohd Nordin Adlan ◽

Khiruddin Abdullah

Keyword(s):

Electrical Resistivity ◽

Ground Water ◽

River Water ◽

Time Lapse ◽

Pumping Test ◽

Riverbank Filtration ◽

Electrical Resistivity Imaging ◽

Production Well ◽

Dynamic Changes ◽

Resistivity Imaging

Riverbank filtration (RBF) is a natural water pre – treatment, safer and cost – effective that uses geology instead of chemicals to pre – treat river water. The process occur during the infiltration process of river water passing through riverbank material towards a production well during a pumping test, where the removal of biological and colloids take place. Abstraction of ground water are required for RBF to occur, hence pumping test were done. As pumping test took place, ground water was in continuous discharging and recharging process throughout time. Objective of this research is to study the dynamic changes of ground water during discharging and recharging process for 72 hours by using time – lapse electrical resistivity imaging (TLERI). Resistivity, which uses current to measure the resistivity of subsurface was used during the pumping test to monitor ground water changes and infiltration of river water during RBF process. Results show significant changes on TLERI data from the first session until the last session. Dynamic changes occurred around the riverbank and production well section while others show less significant changes.

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