Characterization of Aquifers in Lower Gidabo Catchment, Southern, Ethiopia

Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 Characterization of Aquifers in Lower Gidabo Catchment, Southern, Ethiopia Genet Mathewos Messene1 and Mamuye Tebebal Ejigu2 1 Addis Ababa Construction and Housing Development office; Design, Construction and Supervision Core Process, Bole Sub-city, Addis Ababa, Ethiopia; E-mail: genetmathewos7@gmail.com 2 Federal Technical and Vocational Education and Training Institute, Department of Research, Technology Transfer and Industry Linkage, Addis Ababa, Ethiopia; E-mail: bic.ma12@gmail.com Abstract Aquifer characterization is indispensable for active development and management of ground and surface water resources. The important characteristic of groundwater rectification is the capability to determine accurate estimation of aquifer hydraulic characteristics. It is important to deliver a common intelligences for exchange of ideas. Yet, groundwater potential study and aquifer characterization is rarely conducted in Lower Gidabo catchment. Topographically, the catchment is undulated ranging from 1170 m of low flat lands near Lake Abaya to 3200 m AMSL. In this study, groundwater prospective of the catchment was assessed in terms of aquifer characteristics with hydraulic conductivity, transmissivity and storativity. The study targeted to contribute detailed aspect of aquifer hydraulic properties and hydrogeological features in the catchment. Arc GIS 9.3 and Aquifer test programs were used for the study. Hydraulic conductivity of the aquifer ranges from 3.5*10-4 to 2.91*10-3m/day. Likewise, the transmissivity and storativity are ranged from 1*10-3 to 1.05*10-1 m2/min and 8.29*10-5 to 4.11*10-3 respectively. The major aquifer units of the area are weathered and fractured basalts. These types of aquifer formation are recognized to be good groundwater formations. As per the result perceived, hydraulic properties and lithological formation of an aquifer are variable throughout the catchment. Key word: Groundwater potential, Aquifer Test, Lower Gidabo catchment, Aquifer characterization; Lithological formation. 1. Introduction Groundwater is the largest source of fresh water in the world. In many parts of the world, especially where surface water supplies are not available; for domestic, agricultural and industrial water needs can be met by using the water beneath the ground (Kumar, 1997). Many major cities and small towns in the world depend on groundwater for water supplies, mainly because of its abundance, stable quality. Besides, it is inexpensive to exploit particularly in scarce surface water supply area (Morris et al., 2003). One of the fundamental conditions for the growth and development of a nation like Ethiopia is certainly the progressive fulfillment of its most urgent water needs (Tamiru, 2006). Ethiopia is known with good water potential, however quit a small Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 129 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ portion of this resource is presently developed in the rural areas; the limitation being too high initial development cost. Previously developed groundwater sources are used primarily for drinking water supply, it offers access to safe water for approximately 40-80 percent of the water supply provided to the urban population, and it is the largest fresh water source in the country. Despite, the high initial cost, groundwater is increasingly becoming an important source of drinking water supply (Getachew, 1998). The important feature of groundwater improvement is the capability to determine exact estimations of aquifer hydraulic characteristics (Paul, 1993). Aquifer characterization is essential for effective ground and surface water development and management (Wittenberg and Sivapalan, 1999). Aquifer characterization is vital to provide a common considerate for discussions. It is developing sufficient understanding of an aquifer or group of aquifers to support decisions affecting the groundwater resource. It is imperative for understanding the major hydrologic processes and hydrogeological properties that govern the occurrence, flow and replenishment of water through and out of an aquifer. These parameters are estimated through pumping tests carried out on water wells. The hydraulic properties estimated with the aid of aquifer test for the well field design phase to clear the most efficient design (Layen, 2014). Hydraulic properties of an aquifer can be determined by conducting aquifer tests and measuring the specific capacities of wells (Lucy, 2013). In some illustrations, groundwater monitoring wells may not be present onsite to conduct pumping or slug tests. In these e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 situations, it is acceptable to obtain an estimate of the aquifer properties based on engineering and geological material descriptions as well as from correlations between these descriptions and some commonly measured soil properties. The area under the study comprises parts of Lower Gidabo River catchment in Sidama and Gedeo Zones. Water is basic for socio-economic development of the people whose income is primarily dependent on agriculture. However, due to drought, poor water supply and sanitation services; several socio-economic activities are reduced. Similarly, most of the residents living in the area are rural people whose livelihood is mainly dependent on agriculture with poor water supply and sanitation services. Large part of the catchment is suitable for agricultural activities and settlement. Nevertheless; it is affected by flooding, erosion and sedimentation problems. With rising population growth in the catchment, the consumption of water supply is advanced, which rely on the sources of ground and surface water to meet the demands of water supply. Further, the fast growing of industry and residential needs extra water mainly in dry season. Accordingly, the stockholders are concerned in the development of groundwater supply projects. Thus, a better understanding of the hydraulic properties of an aquifer is vital for groundwater development. The gap of understanding aquifer characteristic and hydro-lithological formations are the factors in developing groundwater supply projects. Therefore, assessment of aquifer characteristics in the catchment is a main approach for improving the use of groundwater resource. The study was Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 130 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ conducted on aquifer characterization in Lower Gidabo catchment. It was addressed to understand the characteristics and types of aquifer formation in the catchment. This study provides vital information about the aquifer, which is ready to lend a hand in the possible development and management of water resource in the catchment. 2. Materials and Methods 2.1 Description of the study area The study was carried out in Lower Gidabo catchment, Abaya Chamo Subbasin, SNNPR, Ethiopia. It is located between 6°39’N to 6°12’N and 38°14’E to 38°21’E covering an area about 1047.5 km2. The altitude of the catchment ranges from 1170 to 3200 m AMSL. Lower e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 Gidabo catchment contains 38 sub-basins which includes some tributaries that contribute to the Gidabo River. The study area lies in six Woredas which are found in Sidama and Gedeo zones viz. Aleta Wendo, Aleta Cuko, Wenago, Dilla, Dara, and Bule woredas. The climate ranges from Woina Dega to Dega, it is generally characterized by subtropical Woina Dega on the rift floor and temperate to humid Dega climatic zones on the escarpment and adjacent highlands. The mean annual rainfall and temperature is 1,100 mm and 20°C respectively. The slope of the catchment rages from 0 to 91 percent. The catchment area is covered by 73.3% of intensively cultivated land, 9.5% moderately cultivated land, 14% shrub land, 1.7% marsh land and 0.16% forest. Figure: 1 Location map of Lower Gidabo catchment Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 131 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ 2.1.1 Soils Soil property determines the water storage capacity and affects the resistance of water flowing into the deeper layers. According to FAO (1988) soil classification, the e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 major soil units in the catchment are hromic luvisols, Eutric Leptosols, Eutric Vertisols, Humic Nitisols and Lithic Leptosols (Figure 2).The soil classification and its area coverage are discussed in Table 1. Table: 1 Soil classification and area coverage Soil type Lithic Leptosols Chromic Luvisols Eutric Vertisols Eutric Leptosols Humic Nitisols Total Symbol LPq LVx VRe LPe NTu Area (Km2) 670.77 76.83 245.24 49.94 0.70 1047.5 Area (%) 64.28 7.36 23.50 4.79 0.07 Soil texture Sandy loam Loam Clay Sandy loam Loam Figure: 2 Soil map of Lower Gidabo Catchment 2.1.2 Geology The geology of Lower Gidabo catchment is classified in seven geologic formations Viz. Trachytic basalt and Rhyolit (NQs), Terrace gravel deposits (PNv), Nazareth group Alkaline and per alkaline stratoid silicics (N1_2n), Dino Formation (Qdi), Pyroclastic fall deposit (Qvs), Transitional mildy alkaline (Pv) and Bofa Basalts (N2b). The catchment is dominantly covered by Trachytic basalt and Rhyolit formation. The geological formation of the study area is shown in Figure 3 and Table 2. Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 132 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 Table: 2 Geologic formation and its area coverage Type Dino Formation Transitional mildy alkaline Nazareth group Alkaline and per alkaline stratoid silicics Terrace gravel deposits Pyroclastic fall deposit Bofa Basalts Trachytic basalt and Rhyolit Total Symbol Qdi Pv N1_2n PNv Qvs N2b NQs Area (km2) 154.68 98.75 165.21 402.36 11.16 13.47 201.84 1047.48 Area (%) 14.80 9.40 15.80 38.40 1.10 1.30 19.30 Figure: 3 Geological map of Lower Gidabo catchment (EMA, 2006) 2.2 Methods 2.2.1 Data sources In this study qualitative and quantitative data were collected from secondary sources. The data were collected from Minister of Water, Irrigation and Energy, Ethiopian Mapping Agency, South Water Works Construction Enterprise and Sidama Zone Water, Mine and Energy Department. The data that were utilized in the study includes; completion reports of pump test boreholes data (i.e. location of the well, aquifer properties data, well dimensions, water level data, pumping test hours), geologic well log data, features of boreholes and hand dug wells, topographic map at the scale of 1: 50000, geological and soil data. 2.2.2 Data analysis and interpretation The methods employed to acquire efficient information for investigating groundwater potential of the study area such as; generation of thematic maps to present slope, soil, geologic formation and aquifer characterization were analyzed using, Arc GIS 9.3 and Aquifer-Test 2015 programs. Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 133 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ 2.2.2.1 Aquifer characterization The aquifers of the catchment were characterized based on geologic materials and aquifer hydraulic properties. It was analyzed by using the secondary data of borehole lithological log data, surface geological units and aquifer hydraulic properties. Aquifer parameters were estimated with Aquifer-Test 2015 software by using six bore holes pumping test data that are located in six Woredas of the catchment. According to Cheini et al. (2008, cited in Week, 2005; Stefans and Vitaly, 2005) the pumping test data analysis and interpretation are used as a method for estimating the hydrological properties of the aquifer. Estimation of these parameters permits quantitative prediction of the hydraulic response of the aquifer to recharge and pumping. An aquifer test is a precise experiment which was used to determine basic aquifer parameters such as Hydraulic conductivity (K), Transmissivity (T) and Storativity (S) in the district of a pumping well data (Bear, 1979). The general e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 approach for analyzing the aquifer-test data for this study was to match the simulated time-drawdown solution with the two analytical methods. The pumping test data were taken from the well completion reports of the bore holes located in Aleta Wendo, Chuko, Wenago, Bule, Dilla and Dara Woredas. To evaluate the constant rate drawdown test; Cooper and Jacob I solution method in a confined aquifer were used for identification of aquifer parameters viz. Transmissivity and Storativity of the well. However, Hydraulic conductivity of the aquifer was analyzed based on Hvoslve’s slug test solution method. Hydraulic conductivity Hydraulic conductivity is the rate of flow under a unit hydraulic gradient through a unit cross-sectional area of an aquifer. It is a measure of materials capacity to transmit water in the soil (SFWMD, 2009). Hydraulic conductivity of an aquifer was estimated based on Hvorslev (1951) slug test analysis method (SWS user manual, 2011). Table: 3 Ranges of hydraulic conductivity in different rocks/ soils (Tenalem and Tamiru, 2001 and Lewis et al., 2006) Lithology Clay Silt Sand Gravel Limestone, dolomite Friable tuff K= r ln Hydraulic conductivity (m/day) 5*10-7 - 10-3 10-3 - 10-1 10-1 - 5*102 5.00- 5*104 5.00*10-6 - 100 2.00*10-2 – 2 L R LTi Where K is hydraulic conductivity in m/day, L is screen length in m; Ti is the time lag when ht/h0= 0.37 in day; R is radius of the well including the gravel pack and r is effective radius of the piezometer in m. Lithology Welded tuff, ignimbrite Dense basalt Fractured basalt Fractured crystalline rock Volcanic rock Hydraulic conductivity (m/day) 5*10-5 - 2*10-1 10-6 - 10-3 10-4 – 1 10-3 – 10 Almost 0 - 103 Transmissivity Transmissivity is the rate of flow under a unit hydraulic gradient through a unit width of saturated thickness of the aquifer. It is a measure of the capability of the aquifer to transmit groundwater through a one meter wide band over its full depth Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 134 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ under unit gradient. All the transmissivity were ultimately calculated using the slope of time-drawdown data plotted on semi log paper. According to Cooper and Jacob I T= e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 time-drawdown analysis the transmissivity of an aquifer related to its hydraulic conductivity are calculated as (Rushton, 2003): . Q ΠΔS Where, T is transmissivity in m2/s, Q discharge of the well in m3/s and ΔS is change in drawdown per log cycle. Table: 4 Classification of transmissivity (Krasny, 1993) T (m2/day) >1000 100-1000 10-100 1-10 0.1-1 < 0.1 Designation Very high High Intermediate Low Very low Imperceptible Groundwater supply potential Regional importance Lesser regional importance Local water supply (small communities, plants etc.) Smaller withdrawal for local water supply (Private consumption) Limited consumption Very difficult to utilize for local water supply Class I II III IV V VI Storativity (Storage coefficient) Storativity is a measure of the amount of water in a confined aquifer; it will give up for a certain change in head. As per Schlumberger Water Services (2011, cited in Cooper and Jacob, 1946) and Rushton (2003) the storativity of an aquifer is analyzed with Cooper and Jacob I timedrawdown method. The storativity of a confined aquifer varies with specific . Tto S= r Where, T is transmissivity of the aquifer; r; distance from well to piezometer and T is time in the starting of pumping to which the set of drawdown data correspond. Besides, the identification of an aquifer type was allowed by comparing its drawdown versus time curve with that of the Cooper and Jacob I theoretical model curves. Based on the type of theoretical model curves plotted, the type of aquifer storage and aquifer thickness, usually it ranges from 5x10-5 to 5x10-3 (Todd, 1980); yet in unconfined aquifers, storativity ranges from 0.1 to 0.3 (Lohman et al., 1972). It is approximated in semi-log distribution. was identified. The plotting of drawdown versus time graphs are schemed in linear scale in meter and second unit respectively. It was plotted through pumping test records. To identify surface geology of the catchment, 1:500,000 scale geological map was utilized. The hydrogeological map of the study area was also made from these geologic units to hydrologic unit. A Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 135 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ borehole geological log is constructed from sampling and inspection of well cuttings collected at frequent intervals during drilling the test holes. Such logs provided a picture of the geological character and thickness of each stratum encountered as a function of depth (Afewerk, 2011, cited in Todd and Mays, 2004). 3. Result and Discussions 3.1 Aquifer characterization by using surface geology The surface geological units found in the catchment are characterized in both primary and secondary porosities such as; trachytic basalt and rhyolite, Nazareth group alkaline and per alkali stratoid e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 silicics, Dino formation, pyroclastic fall deposit, transitional mildy alkaline, Bofa basalts and terrace gravel deposits (Figure 4). The hydro-lithologic units of the catchment are mainly classified as volcanic and alluvial aquifer formations. The volcanic aquifer principally presents in the escarpment and highlands, while the alluvial aquifer is inhabited in the valley floors of the catchment. Eastern parts of the catchment are covered by highly fractured and weathered basaltic rock formations in highlands and cliffs. The high degree of fracturing and weathering and its high topographic nature results the rock to be a recharge zone in the Eastern side of the study area. The major geological units identified in the catchment are discussed as follows: Legend Contour lines Groundwater flow direction Nazareth group alkaline and per alkali stratoid silicics Bofa basalts Terrace gravel deposits Trachytic basalt and Rhyolit Transitional mildy alkaline Dino formation Pyroclstic fall deposit Figure: 4 Hydrogeological map of the Lower Gidabo catchment Trachytic basalt and Rhyolite (PNv) This type of geological unit spreads from the central to the south western parts of the catchment (Figure 4). It covers about 19.3 percent of the study area (Table 2). Trachytic basalt and Rhyolite are the second dominant geological units in the catchment next to Terrace gravel deposits. These geological materials often have characteristics of irregular steam cavities which make the broken surfaces of specimens of these rocks rough and irregular. According to WRCS (2013) Trachytic basalt and Rhyolite usually Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 136 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ consist of Sani dine feldspar in principal extent; and low to moderate potential aquifer of welded tuff and lacustrine sediments. e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 formation are placed in highly weathered and some sections show series of weathered layers. Terrace gravel deposits Dino Formation (Qdi) This type of formation is ignimbrite, which is light gray colored that out crops stratigraphically above the Nazareth group Alkaline and per alkali stratoid silicics. The Dino formation is either with tuff mostly or pumice. Dino formation ignimbrite has some obsidian rich layers medium to fine grained in most cases. It locates in the northern parts of the catchment (Figure 4); covering with 14.8 percent of the study area (Table 2). Bofa Basalts (N2b) This type of formation is situated in the middle and western parts of the chachment (Figure 4). It is covering about 1.3 percent of the study area (Table 2). It is likely to affecte with fault and joint which have positive impact for groundwater recharge and storage. It forms well developed and interconnected joint sets that form boulder type of basalt; and relatively massive joints developed along the flow layers (WRCS, 2013). Nazareth group Alkaline and per alkaline stratoid silicics (N1_2n) A Terrace gravel deposit is situated dominantly in the eastern parts of the study area (Figure 4). This type of formation covers the largest area of the catchment, which comprises about 34.4 percent of the catchment (Table 2). A terrace consists flat and gently sloping geomorphic surface which mainly have gravel formation. Pyroclastic fall deposit (Qvs) A pyroclastic fall is situated in the Middle Western part of the study area (Figure 4). This type of formation is covered relatively the smallest portion of the catchment, it consists about 1.1 percent of the total area (Table 2). It is composed of silt sand, silt clay and gravely sand soil textures. Transitional mildy alkaline (Pv) The transitional mildly alkaline is located in the northeast and southeastern edge of the catchment area (Figure 4), which is comprised nearly 9.4 percent of the study area (Table 2). This type of formation is usually weathered, fractured and jointed. 3.2 The Nazareth group Alkaline and per alkaline stratoid silicics are located in western parts of the catchment. As it presented in Table 2, this formation covers nearly 15.8 percent of the study area. The rock is fractured and exposed due to northeast and northwest trending faults (WRCS, 2013). The rocks of this Aquifer characterization by using borehole lithological log Classifications of hydrogeological units were done for characterization of the aquifer. The aquifers of the catchment are dominantly covered with weathered and fractured basalt. These types of aquifers are found with an average depth and Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 137 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ thickness of 108m and 19.5m respectively. The other main aquifer formation materials comprised in the well covering an average depth and thickness of 84m and 12.7m gravel, tuffaceous sediments and rhayolite with 90m and 8m respectively. According to the borehole lithological log data, the main aquifer type in most of the wells are weathered and fractured basalts. As per the well completion reports, weathered and fractured basalt of many wells are tapped at depth ranges about 40 meters to 162 meters, where 40 and 162 30 60 90 120 e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 meter water depths of the well strike at Sokicha well #3 and Aleta Wendo well #2 respectively. Regarding to the well completion reports, the lithological data indicates the presence of confined aquifers in the catchment. Some of the wells situated in northern part of the catchment (i.e. Aleta wendo #3) have identical aquifer formation viz. weather and fractured basalt with the wells located in the southern part of the catchment. The distribution of the boreholes in the catchment are shown in Figure 6. 150 162 Figure: 5 Water wells location map Vertical distribution of the well log data are presented in Figure 9. It displays that as moving from northern part of the catchment where the wells situated in Aleta Wendo (i.e. Aleta wendo #2 and #3) to the south of the catchment where the wells located in Dara (Sokicha # 1, 2 & 3) and Bule Woreda (Bule #1 & 2), the common hydrogeological unit found in the area is fractured and slightly weathered basalt. The thicknesses of basaltic aquifer in Aleta wendo #2 and Aleta wendo #3 wells are 58.23 and 86.5 meters and that of Bule #1 and 2; Sokicha # 1, 2 and 3 is 13, Figure: 6 Vertical distribution of aquifer formations from well logs data 16, 2.7, 16, 17 and 5 meters respectively. This shows that the thinner thickness of an aquifer is the lesser groundwater storage capacity. It indicates that an aquifer is rich in groundwater as we go from southern to western and north western part of the catchment. The aquifer formations are comprised lacustrine sediments; weathered and fractured volcanic rocks, which are classified as high, moderate and low permeability respectively. The major water bearing formations in all of the boreholes Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 138 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ are summarized as lacustrine and alluvium (gravel, sand and silt) sediments. There are two types of aquifer system distribution in the catchment, viz. shallow and deep aquifer systems. The shallow aquifer system ranged from 18 to 54 meters depth the formation includes lacustrine sediments (sand and gravel), volcanic sand and ash, weathered basalt, quartz sand, ignimbrites and tuff. The deep aquifer system is encountered at the depth range of 55 to 232 meters and the types of aquifer 10 100 0 Time [s] 1000 10000 found are coarse gravel, boulders, tuff, fractured ignimbrites, massive basalts and weathered ignimbrite. 3.3 Aquifer characterization by using pumping test data Time versus drawdown graph of the wells using Cooper and Jacob I solution method for Aleta Wendo # 2, Bule #1, Kore #1, Teferi kela, Wenago #2 and Rufo Debeka wells plotted on semi-log paper are presented in Figure 7. 100000 0.1 0 2 3 4 5 10 Time [s] 100 1000 10000 20 30 40 50 (a) Aleta wendo well #2 Time [s] 10 100 1000 10000 0 (b) Bule well #1 100000 10 0 6 12 18 24 30 Time [s] 1000 10000 100000 20 30 40 50 (c) Kore well #1 10 0 100 10 Drawdown [m] Drawdown [m] 1 10 Drawdown [m] Drawdown [m] 1 100 Time [s] 1000 10000 (d) Teferi Kela well #1 Time [s] 100000 10 100 1000 10000 100000 0 4 10 Drawdown [m] Drawdown [m] e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 8 12 16 20 20 30 40 50 (e) Wenago well #2 (f) Rufo Debeka well #2 Figure: 7 Time verses drawdown graph of the wells with Cooper and Jacob I solution method Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 139 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ The six boreholes (i.e. Aleta wendo #2, Bule #1, Kore #1 and Wenago #2, Rufo Debeka and Teferi Kela wells) are illustrated nearly similar curves (Figure 7). Depending on the time drawdown graph and the borehole lithological data, the aquifer corresponding to them adheres to the wells revealed to be confined aquifers. For several wells, there were no extensive raise of the static water levels above the e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 water strike depth, indicating the occurrence of confined aquifer in the catchment. Transmissivity The transmissivity of an aquifer is calculated using equation (2). The values of transmissivity analyzed using Aquifer test program from pumping test data are given in Table 5. Table: 5 spatial distribution of transmissivity Location Aleta Wendo Bule Rufo Debeka (Chuko) Teferi Kela (Dara) Wenago Korie (Chuko ) Average Project No_ AW2 B1 AC2 D1 WS2 AC3 Thickness of aquifer (m) 6 29 21 30 36 27 The transmissivity distribution in the aquifer is highly variable, its estimated value are ranged from 6.43*10-8 to 9.16*10-3 m2/s. The transmissivity of an aquifer in Rufo Debeka well #2 is 9.16*103 , which is the highest value over the other wells (Table 5). This indicates that, this site has the greatest potential for productive aquifers. According to Krasny (1993) transmissivity classification, the transmissivity of aquifer is existed in intermediate range. Thus, the well could be maintained for local water supply (small communities, plants). However, the transmissivities of aquifer in Bule #1 and Teferi Kela # 2 are very low, which is found in the rang 0.1 and 1m2/day (Table 5). Likewise, the transmissivity of aquifer in Wenago #2 and Korie #3 wells are low; it implied that smaller withdrawal of water Type of aquifer Confined Confined Confined Confined Confined Confined T ( m2/s) 6.43* 10-8 8.22*10-5 9.16*10-3 3.18*10-4 1.96*10-3 1.36*10-4 1.96*10-4 for local water supply (private consumption) can be preserved in the wells. Groundwater supply in Aleta Wendo # 2 is very challenging for local water supply; because the transmissivity of an aquifer is unrealistic. The aquifer is underlined by clay formation at six meter depth, which provides impermeable basement formation in the aquifer. In general, confined condition of an aquifer is existed in all the six wells located in the catchment down dip of their outcrops. The overall average transmissivity of the well is found to be 1.96*10-4 m2/s. Hydraulic conductivity Hydraulic conductivity of an aquifer was determined using equation (1). The analyzed value of hydraulic conductivity is presented in Table 6. Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 140 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 Table: 6 estimated values of hydraulic conductivity and storativity Location Aleta Wendo Bule Rufo Debeka (Chuko) Teferi Kela (Dara) Wenago Korie (Chuko ) Average Project No_ AW2 B1 AC2 D1 WS2 AC3 With regard to the available data, hydraulic conductivity of aquifer in the study area ranged from 1.04*10-7 to 3.13*10-1 m/day with an average value of 5.43*10-2 m/day (Table 6). The value is highest in Rufo Debeka well #2 in western parts of the catchment, it implied that the aquifer materials around the boreholes of Rufo Debeka well # 2 is the highest permeable, whereas lowest value of hydraulic conductivity is existed in Bule well #1 in south eastern of the escarpment. According to Lewis et al. (2006) and Tenalem and Tamiru (2001) discussed in the ranges of hydraulic conductivity with lithology, the aquifer material found in the catchment close to Aleta Wendo #2, Rufo Debeka #2 and Chuko (Korie) #2 are fractured basalt, welded tuff and ignimbrite dominate. However, hydraulic conductivity of Bule well #2 is 1.04*10-7 (Table 6). As it can be seen from the result, the hydraulic conductivity of the well is relatively low; the aquifer formation is associated with dense crystalline rock material. Hydraulic conductivity of the boreholes of Teferi Kela and Wenago #2 are found in the range of 5*10-5 to 2*10-1m/day, which is dominantly associated with Welded tuff and ignimbrite lithological formation (Table 4). K ( m/day) 8.57*10-3 1.04*10-7 3.13*10-1 3.35*10-4 2.91*10-3 2.94*10-4 5.43*10-2 S 1.18* 10-6 9.64*10-4 2.02*10-14 4.08*10-4 4.24*10-10 9.51*10-12 2.29*10-4 Storativity (Storage coefficients) The storativity of an aquifer is calculated using equation (3). The analyzed values of storativity are given in Table 6. The result ranges from 2.02*10-14 to 9.64*10-4 with an average value of 2.29*10-4. This result covers the range of confined values of an aquifer. The borehole’s tapped in dense crystalline rock formation in the southeastern hill side of the study area shows highest value of storativity (Table 6). Whereas, the well’s located in the western lowland parts of the catchment closes to Rufo Debeka well # 2 are presented with lower value of storativity. Regarding to the storativity of boreholes given in the Table 6, storativity of an aquifer decreases from northeast to northwest of the study area. Likewise, storativity of an aquifer increases moving from southeast highlands to central parts of the catchment. 4. Conclusion and Recommendations Groundwater potential study is vital to promote implementation of appropriate technologies mainly in water deficient areas to mitigate water scarcity problems. The results of this study are substantial in filling the gap of understanding groundwater perspectives. As per the Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ Page 141 Journal for Studies in Management and Planning Available at http://www.edupediapublications.org/journals/index.php/JSMaP/ results, Trachytic basalt and Rhyolites are the predominant hydrogeological units in the study area. As the boreholes lithological log data demonstrated, the major aquifer formations are weathered and fractured basalt rocks. The aquifers of the catchment have two systems, viz. shallow and the deep aquifer systems. From lithological data of some shallow aquifer systems, it is observed that the aquifer depth ranges between 18 and 54 meters. The major constituent geological materials of this aquifer system are fractured and slightly weather basalt, lacustrine and alluvial sediments. The deep aquifer system occurs in the range of 54 to 232 meters. In this system, the major elements of an aquifer are lacustrine and alluvium sediments; weathered and fractured ignimbrite and basalt, welded tuff coarse gravel and boulders, pumice and massive basalts. These different aquifer formation have unlike permeability states in the catchment in the range of high, high to medium, moderate; low to moderate and low respectively. As per the well completion reports of the boreholes; it has confirmed that the aquifer is found in confined formation. Regarding to the pumping test data of the boreholes, the study area is categorized in to different hydraulic conductivity zones; it is ranged from 1.04*10-7 to 3.13*10-1 m/day. The value is high in southeaster parts of the catchment. The transmissivity of an aquifer ranges from 6.43*10-8 to 9.16*10-3 m2/sec. It is advanced from plateau to the low-lying areas of the catchment. The wells tapped in fractured basalt, basalt and ignimbrites lithological formation in the central and northern part of the catchment have the lowest value of e-ISSN: 2395-0463 Volume 02 Issue 7 July 2016 transmissivity (6.43*10-8 to 3.69*10-4 m2/sec); whereas in ash, massive basalt and coarse grained gravel boulders found in southern and south western parts of the catchment have maximum value of transmissivity (3.69*10-4 to 9.16*10-3 m2/sec). Therefore, this lithological formation and hydraulic properties of an aquifer information will be convenient for tangible identification of suitable locations for extraction of water and used as a guideline for further groundwater potential study. 6. References Afework, D. (2011). Groundwater Potential Evaluation And Flow Dynamics of HormatGolina River Catchment, Kobo Valley, Northern Ethiopia. Addis Ababa, Ethiopia. Bear, J. (1979). Hydraulics of Groundwater. McGraw-Hill, New York, p 569. Cooper, H.H. and Jacob, C.E. (1946). 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