Water leakage investigation of micro-dam reservoirs in Mesozoic sedimentary sequences in Northern Ethiopia (original) (raw)
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ABSTRACT The study was conducted to assess the main causes of leakage problem in the Hashenge micro-dam, located in the Tigray regional state, northern part of Ethiopia. The micro dam is a 19 m height earth fill dam with the length of 387 m and reservoir capacity of about 2.3 million cubic meters at maximum water level. Geological, geophysical and engineering geological investigations were conducted in the abutment and reservoir area to assess and pinpoint the main causes. The dominant lithologic units include limestone-shale-marl intercalation, dolerite and recent soil deposits. Vertical electrical sounding was used to locate geotechnical boreholes and to know vertical and lateral variability of geological materials. Geotechnical and engineering geological investigation including drilling of three boreholes and packer testing along with detail measurement and analysis of discontinuity parameters was conducted. Analysis of the data shows that the sedimentary succession, limestone-sh...
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
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...
Leakage paths at the Lar Dam site, northern Iran
Quarterly Journal of Engineering Geology and Hydrogeology, 2017
The Lar Dam was constructed from 1974 to 1980 in the Lar River valley at the foot of the Damavand Volcano. The valley walls consist of Mesozoic limestone and Quaternary volcanic rocks, overlain by thick lacustrine deposits. Prior to dam construction, a few sinkholes were observed in the reservoir area, but after impoundment, several new sinkholes formed and leakage occurred through downstream springs. Despite extensive treatment works, the reservoir has currently impounded only 40% of its designed capacity, about 35 years after the commencement of operations. The Lar Reservoir is located inside the area of a large palaeo-lake, which formed as a result of blockage of the river valley by eruption of the Damavand Volcano during the Pleistocene. This lake existed for thousands of years, developing deep karst conduits in the limestone below the volcanic rocks toward downstream springs. With the construction of the Lar Reservoir, relict karst conduits were revived and leakage occurred. Two paths are proposed for reservoir leakage, considering the region's historical geology, present hydrogeological setting, tracer tests and isotopic studies, as well as the response of spring discharge and borehole water level to reservoir filling.
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.
Potential leakage at the Khersan 3 Dam Site, Iran: a hydrogeological approach
Bulletin of Engineering Geology and the Environment, 2006
The paper discusses the investigations into the Khersan 3 Dam site in the Zagros Zone, southern Iran, where the Rig, Shorom and Laki Anticlines meet. The Asmari Limestone is the main aquifer system in the area of the dam site and its reservoir. Marly bands within the Lower Asmari Unit create three confined sub-aquifers under artesian pressure overlain by one unconfined sub-aquifer. The impounded water will be in direct contact with the Asmari Limestone hence leakage may occur through existing karst features. As the recharge zone of the artesian sub-aquifers is higher than the normal water level in the reservoir, no direct leakage through the artesian sub-aquifers is anticipated. However, when the water head in the unconfined sub-aquifer rises with the construction of the dam, leakage may occur and further karstification develop. Keywords Leakage Á Karst aquifer system Á Hydrogeology Á Zagros Zone Á Iran Ré sumé L'article pré sente les travaux de reconnaissance ré alisé s sur le site du barrage de Khersan 3, dans la ré gion du Zagros au sud de l'Iran, au niveau des anticlinaux de Rig, Shorom et Laki. La formation des calcaires d'Asmari est le principal systè me aquifè re au niveau du site du barrage et de son ré servoir. Des niveaux marneux dans la partie infé rieure de l'unité d'Asmari sont à l'origine de trois nappes captives surmonté es par une nappe libre. L'eau de la retenue sera en contact direct avec les calcaires d'Asmari et, de ce fait, des fuites pourront avoir lieu au travers du karst. Comme la zone de recharge des nappes captives est plus haute que le niveau normal du ré servoir, on ne craint aucune fuite au travers des aquifè res correspondants. Cependant, lorsque la charge hydraulique dans l'aquifè re de la nappe libre augmentera avec la construction du barrage, des fuites pourront avoir lieu et la karstification pourra se dé velopper. Mots clés Fuite Á Aquifè re karstique Á Hydrogé ologie Á Ré gion du Zagros Á Iran
Sources of leakages at Al-Jumine Dam, NW Tunis, Tunisia
2000
Al-Jumine Dam (90 m high, 600 m long and 60 km NW of Tunis, Tunisia) is constructed on a nonperennial stream, which is storing more than 130 million cubic meters of water (irrigation and drinking for Tunis and Bizerte). Collected data from two drains, piezometers, injected tracers and environmental isotopes were interpreted to determine the possibility and extent of leakage (from the dam) as well as the different types of groundwater intercepted at varying distances from the site. The interpretation of the aforementioned data showed a sizable front of water leaking (at a rate decreasing away from the dam site) and that this fresh water front is being mixed with a local groundwater of higher salinity .The water seepage might constitute a potential risk threatening the integrity of Al-Jumine Dam.
Engineering Geology, 2015
La Loteta Reservoir, with a storage capacity of 105 hm 3 , is located in a large karst depression around 6 km long on the southern margin of the Ebro River valley, NE Spain. Geomorphological mapping and borehole data indicate that the development of the basin is related to subsidence due to interstratal dissolution of the underlying halite-and glauberite-bearing evaporites. The dam site corresponds to the water gap carved by the small drainage that captured the formerly internally drained depression. Here, the foundation and abutments of the dam include a horizontal and laterally extensive gypsum unit 11 m thick. This sedimentary package showed considerable evidence of karstification in the excavation carried out during the construction of the dam, especially in the left abutment, where it was largely removed. The watertightness system of the ca. 1.5 km long earth dam includes a vertical clay core, a horizontal clay blanket, a cut-off wall, and grout curtains 675 m and 255 m long on the left and right abutments, respectively. Multiple data including leakage discharge measured in the different zones of the drainage system, seepage points mapped downstream of the dam, borehole and piezometric data, and an equipotential map, reveal that leakage essentially occurs through the gypsum unit. The main leakage occurs beneath and next to the left edge of the dam body. This water loss and the associated enlargement of karst conduits are also supported by settlement measured on the dam crest and the occurrence of sinkholes within the reservoir, next to the left abutment. Additional seepage across the grout curtain in both abutments is also identified. Although unlikely, there is also the potential for the water to escape towards an adjacent watershed, where the base level is located below the maximum water level of the reservoir. An additional cut-off wall has been projected to block the main leakage path.
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 ...