Geological, geophysical and engineering geological investigation of a leaky Micro-dam in the Northern Ethiopia (original) (raw)
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Journal of African Earth Sciences, 2017
Highlights Geological factors considered into account in reservoir water leakage. Vertical electrical sounding and profiling integrated with other data for leakage zone delineation. Discontinuities, bedding planes and regional faults play a great role in leakage problems localized in sedimentary basins. Regional and local geology and hydrogeology have played a major role in the planning, design, construction and performance of the MDRs. Geological and geophysical investigation of water leakage from two micro-dam reservoirs: implications for future site selection, northern Ethiopia
Journal of African Earth Sciences, 2013
Millions of people throughout the world depend on dam reservoirs for domestic water supply, irrigation, electricity and flood protection. In the last two decades, 54 micro-dam reservoirs have been constructed in Northern Ethiopia to fight the recurrent drought and improve agricultural productivity through irrigation. However, about 60% of these micro-dam reservoirs are suffering from excessive leakage. Comprehensive studies have been carried out on two micro-dams to assess and pinpoint the causes of leakage. Arato and Hashenge micro-dams located in Northern Ethiopia have 20 m and 19 m height, and 2.59 Mm 3 and 2.23 Mm 3 reservoir capacities respectively. Observational geological description, shallow hand dug test pits, vertical electrical sounding and drilling of geotechnical holes were used to understand the overall geological, engineering geological and geo-hydrological setup of the area. The different methods applied, such as discontinuity analysis, geophysical surveys, drilling and packer tests, delivered results that were found to be in close agreement and led to the identification of the leakage zone. The geological units found in both sites are limestone-shale-marl intercalation, dolerite and recent soil deposits. The research results revealed that the limestone-shale-marl intercalation unit is heterogeneous and shows alternating sequences. Analysis of the different data shows that the limestone-shale-marl intercalation is a pervious unit (hydraulic conductivity in the range of 10 À4-10 +2 cm/s) and was found to be responsible for the excessive leakage of the micro-dams. It is hoped that the observations, data and insights gathered from these case studies will enable to plan technically and economically viable anti-leakage measures for these schemes and help for future new site selection and design activities in the region and other regions with a similar geological environment.
Momona Ethiopian Journal of Science
Leakage is one of the major problems facing the functionality and sustainability of dams. It occurs through the embankment body, reservoir, foundation, and abutments. This study was conducted to identify the main causes of the leakage problem at the Dora-1 dam, located in the northern part of Ethiopia. It is an earthfill dam with a height of 43.5 m, crest length of 454 m, and reservoir capacity of 4.67 million cubic meters. Part of the embankment body was wet and swampy up to 20 m high from the ground due to leaking water. Geological investigation, laboratory test of the construction materials (including grain size analysis, specific gravity and water absorption, Atterberg limit, free swell, dispersion, permeability, and shear strength), and electrical resistivity investigation were used to identify and pinpoint the possible causes of the leakage problem. Results of the study show that the favorable geological features responsible for the occurrence of leakage include: (a) geologica...
Bulletin of Engineering Geology and the Environment, 2019
The paper presents results of electrical resistivity imaging and engineering geological investigations conducted at the Gereb Segen dam site and reservoir to evaluate water tightness and stability. A programme of 2D resistivity imaging, discontinuity surveying, core drilling and Lugeon testing was conducted to assess the engineering geological performance of the dam and reservoir area. The geology of the dam site comprises alluvial deposits, dolerite, micritic limestone and marl-limestone-shale intercalation units. The investigations revealed dissolution cavities up to meters in size showing a preferred alignment along the valley; the separate lines of investigation correlated well to provide confidence in the findings. A karstified zone was identified at the base of the marly limestone unit at the dam site. A layer of gypsum found at shallow depth (9.5 m) along the dam axis may pose a dissolution hazard to water tightness and ground quality. Lugeon test results define very-low-to low-permeability units (shale with gypsum lenses and shale-mudstone) and high-permeability units (marly limestone and dolerite) and very-highpermeability zones associated with the karstic features. The presence of discontinuities and/or weak zones at the abutments and cavities at the dam foundation will affect the stability of the dam and facilitate leakage. Multiple line grout curtains for the karst zones and grouting for the jointed limestone at the dam axis and both abutments are recommended to reduce the possible leakage that will occur at the dam.
Journal of Geology & Geophysics, 2020
Gullele Botanic Garden is one of the largest botanical gardens in Ethiopia, which is found northwest of Addis Ababa. For this garden, a dam was proposed to be constructed for irrigation and recreational purposes. The intended dam will have a height of 30 m and a dam axis length of around 180 m. The main objective of this work is to investigate and evaluate the engineering geological aspects of the proposed dam site based on detailed geological, geotechnical and geophysical investigations. The investigation conducted in the area includes, electrical resistivity imaging, VES, borehole drilling and single packer permeability test. Geologically the area is covered by the different volcanic rock such as ignimbrite, rhyolite, tuff, basalt, and residual soil; and geological structures such as joint, fracture, flow banding, and cooling joint. The dominant orientations of geological structures are N-S and E-W directions. Results from different investigations revealed that three geotechnical ...
2019
Gullele Botanic Garden, which is found northwest of Addis Ababa, is one of the largest botanical gardens in Ethiopia. For this garden, a dam was proposed to be constructed for irrigation and recreational purposes. The intended dam will have a height of 30 m and a dam axis length of around 180m. The main objective of this work is to investigate and evaluate the engineering geological aspects of the proposed dam site based on detailed geological, geotechnical and geophysical investigations. The engineering geological investigation conducted in this site includes seismic refraction, borehole drilling and testing. Geologically the area is covered by the different volcanic rock such as ignimbrite, rhyolite, tuff, basalt and residual soil. The geological structures such as joints, fractures, flow banding, and columnar joints were encountered. The dominant orientations of fractures and joints are N-S and E-W directions. Results from different investigations revealed that three geotechnical...
Method of leakage study at the karst dam site. A case study: Khersan 3 Dam, Iran
Environmental Geology, 2006
The excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified. Karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often increases with time. Moreover, karst features may involve the stability of the dam itself. A few operated dam sites at the Zagros Zone encountered a leakage problem. Furthermore, more than 30 dams are presently under study for construction in the Zagros Zone. Karst conditions and leakage potential were investigated at an understudy site (Khersan 3 Dam) for assessing the general methodology for the study of leakage potentials. Conventional methods for studying karst features, geological mapping, geomorphology and extensive borings were applied before the dam was constructed. These methods are not efficient enough to precisely reveal the karst structure, especially hidden and paleokarst, nor the hydrological behaviour of the karst structure in different settings of groundwater flow. Based on the present case study and previous applied approaches by other authors, this paper introduces a methodology by means of karst structure and functioning approaches at local and regional scales that cover the conventional methods and overcome their shortages. The proposed methodology should be applied before construction of a dam and should include three steps (a) recognition of geological and hydrogeological settings, (b) delineation and functioning of the karst system related to the future reservoir, and (c) assessment of the leakage potentials. Following this methodology, the most probable leakage zone(s) and path(s) at the dam site can be highlighted.
Leakage in Bayer Dam in Jordan: Its Causes and Consequences
This research deals with engineering and environmental problems in karst in a geological context. In this study, geologic and geomagnetic investigations have been applied at the site of Bayer dam and revealed severe shallow karstic processes prevailing in the limestone bedrock -under a three meters thick alluvium cover -which forms the unsealed floor of the dam. The measurements done on groundwater of local ancient shallow dug wells in the surrounding of the dam showed the occurrence of fresh water which was attributed to the leakage that took place. The named wells have been known previously to be dry.
Sift Desk Journals, 2016
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.
Geophysical investigation of Ankashasha dam site, Southern Ethiopia
Computational Ecology and Software, 2023
The study area, Ankashasha dam site is found in South Nations, Nationalities and Peoples Regional state of Ethiopia. The overall objective of geophysical investigations in the study area is to assist geological studies to determine the depth of bedrock and estimate the probable seepage that might encounter dam reservoir areas. Vertical Electrical Sounding (VES) and two-dimensional electrical resistivity imaging survey methods were used to assess the safety of the Ankashasha dam. The data were acquired from four VES points using Schlumberger cathode arrays with supreme half current electrode spacing, and two-dimensional electrical resistivity imaging three profile data points were analyzed qualitatively and quantitatively to understand the geology and identify aquifer bearing horizons. The qualitative analysis of VES data was accomplished by using curves, apparent resistivity, pseudo-depths, and the quantitative interpretations of the VES data were constructed by the VES data using IpI-res3, IPI2win and Surfer software and constructing geo-electric section sideways profiles using the result from VES point interpretations and lithological information from the Bedesa borehole. The VES results of the data revealed three geoelectric layers that differ in degree of fracturing, weathering and formation. The bedrock is closer to the surface on the delineated fracture boundaries on the geo-electric section of the NE flanks of the axis. The overburden materials consist of seepage flow paths that widen northeastwards parallel to clay, sandy clay and clayey sand. Seismic refraction work should be forwarded since the area is seismically active to map the structures and determine parameters such as densities of each layer, weak zones, depth to contacts and others. http://www.iaees.org/publications/journals/ces/articles/2023-13(2)/1-Weldeabzgi-Abstract.asp