Groundwater Management for Irrigation in the Raya and Kobo
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Indexed in Scopus Compendex and Geobase Elsevier, Chemical Abstract Services-USA, Geo-Ref Information Services- USA, List B of Scientific Journals, Poland, Directory of Research Journals www.cafetinnova.org ISSN 0974-5904, Volume 08, No. 03 June 2015, P.P.36-46 Groundwater Management for Irrigation in the Raya and Kobo Valleys, Northern Ethiopia NATA TADESSE1, DESSIE NEDAW2, KIFLE WOLDEAREGAY1, TESFAMICHAEL GEBREYOHANNES1 AND FRANK VAN STEENBERGEN3 1Department of Earth Sciences, Mekelle University; 2School of Earth Science, Addis Ababa University; 3MetaMeta, the Netherlands; Email: [email protected], [email protected] Abstract: The study area, Raya and Kobo valleys, are located in the northern parts of Ethiopia. From the hydrological point of view, the sites are located within the Afar drainage basin. The areal coverage of the valleys is 2369 km2 for Raya and 1439 km2 for Kobo. The amount of groundwater that is currently discharged for irrigation purpose in Raya and Kobo valley is 10755.9 m3/day and 30600 m3/day, respectively. This is estimated to be about 0.06% and 6.91% of the total safe groundwater discharge of each valley, respectively. The annual average groundwater recharge in the Raya valley is estimated to be 84 million cubic meters and that of the Kobo valley is 122.9 million cubic meters. At present, the amount of natural recharge in both valleys is more than the abstraction. With regard to the irrigation development in the valleys, the problem is not lack of water; it is rather absence of or poor management. This is mainly due to absence of responsible and efficient institutions that are equipped with adequate capacity. Sustainable management of groundwater resource is indispensable for better development, allocation and optimum utilization of the groundwater resource of the valleys and to avoid any adverse effects. It is therefore necessary to establish responsible and efficient groundwater management system that can undertake not only detailed groundwater management studies of the basins but also effectively implement the on-going irrigation development in the valleys, following the objectives of the national water resources management policy of the country. Keywords: Groundwater Management, Irrigation, Raya and Kobo Valley, Northern Ethiopia. 1. Introduction Concert Engineering and Consulting Enterprise were assigned to undertake the study eight years ago. 1.1. General Kobo pressurized irrigation project was initiated sixteen With the high spatial and temporal variability of rainfall years ago by the Commission for Sustainable in Ethiopia, agricultural development can succeed on Agriculture and Environmental Rehabilitation in sustainable basis with a complete integration and Amhara Region (Co-SAERAR) to tackle the food application of effective/ efficient technologies, insecurity in the valley. Then after, Kobo Girana Valley appropriate institutional arrangements and monitoring Development Program Office (KGVDPO) was systems in order to properly utilize the available water established in 1999 by the Amhara National Regional resources in a certain area. Pressurized irrigation, which State with the aim of enhancing food security through is defined as the application of water through point or irrigation development in the Kobo-Girana valleys. line sources (emitters) on or below and at required discharge rate resulting in partial/full wetting of the soil As it was mentioned in Water Works Design and and plant root, is applied in Raya and Kobo valleys in Supervision Enterprise (2008) Raya valley pressurized northern Ethiopia. irrigation project report, previous studies and drilling was conducted (mostly at the western part of the valley) The Ministry of Water Resources has initiated irrigation by German Consult, Kobo-Alamata Agricultural development study in Raya valley of south Tigray Development Program (1977), Relief Society of Tigray region in 2008 with an aim to efficiently and optimality (1998), Water Well Drilling Enterprise (1998), utilizes the water potential of the area, mainly Ethiopian Institute of Geological Survey (1998), Water groundwater using pressurized irrigation system. Water Works Design and Supervision Enterprise (2005), and Works Design and Supervision Enterprise together with Tekeze Deep Water Wells Drilling Plc (2006). These #02080305 Copyright ©2015 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved. NATA TADESSE, DESSIE NEDAW, KIFLE WOLDEAREGAY, TESFAMICHAEL 37 GEBREYOHANNES AND FRANK VAN STEENBERGEN studies showed that the western part of the valley has National Regional State, Kobo Woreda. It is found at a high groundwater potential. Intensive and integrated distance of 50 kms from the zone town Woldia and 410 study of the Raya valley was carried out in the year km from the regional town, Bahir Dar. The total area of 1996 by Relief Society of Tigray (REST) and the Tigray the sub-basin is estimated to be 1439 km2 of which 29 Regional Government. In the year 1997, feasibility percent is flat plain and the remaining is either report was produced by the Raya Valley Agricultural mountainous or hilly. The project area is bounded by Development Project (RVADP). The Raya and Kobo Tigray National Regional State from north, Alwha sub valleys have also been investigated previously by basin from South, Lasta mountain from west and Zobel different governmental and nongovernmental mountain in the east. The location map of both valleys organizations and scholars such as Dessie (2003), is shown in the Figure 1. Sileshi (2007), Abrham (2009), Mohammedsultan 1.2.2. Geology (2010), Abdella (2011), Abduwassie (2011) and Merhawi (2012). Even though they came up with Raya Valley different values of groundwater recharge estimation of According to the 1998 study of the site by the Relief the valleys, all these previous studies indicated the Society of Tigray (REST) and the 1996 second edition availability of huge groundwater resource on the Geological Map of Ethiopia, the project area is a flat valleys. plain dominated by deep to very deep undifferentiated In both Raya and Kobo valleys, currently the projects alluvial, lacustrine, and beach sediments. These are in the first phase of development. A number of sediments are bounded on the east and west by Ashangi boreholes were drilled and irrigation structures formation, which is a series of volcanic rocks constructed. Farmers are cultivating both cereal and characterized by deeply weathered alkaline (olivine) and vegetable crops using complimentary irrigation system. transitional basalt flows with tuff intercalations, rare Those farmers participating in the irrigation activities rhyolites from fissures and dissected by dikes and sills. are found to have better income and improved life styles. Even though the farmers are getting benefit from this intervention, the sustainability of the project and also the resource itself has to be examined from current development and utilization trend point of view. This step has not been initiated, leading to present study. The present study has been carried out: (a) to study the development and trend of utilization of groundwater and its management in both Raya and Kobo irrigation schemes, and (b) to recommend options for sustainable utilization of the groundwater resources in the Raya and Kobo valleys. 1.2. Description of the Study Area 1.2.1. Location and Accessibility The Raya pressurized irrigation project is located between 12°16' and 12°55' N latitudes and 39°22' and 39°53'E longitudes. It is found at about 600 kms north of Addis Ababa and at 180 kms south of Mekelle, the capital of the National Regional State of Tigray. It is bordered by the Afar National Regional State to the Fig. 1 Location maps Raya and Kobo Valleys. east, the Amhara National Regional State to the south, Kobo Valley part of Ofla and Enda Mehoni Woeredas to the west and Alaje and Hintalo Woredas of Tigray National Regional The valley lies in a region occupied by marginal State. The surface watershed of the valley grabens formed in the escarpment zone of the Afar- approximately covers a total land area of 2369 km2. Ethiopian Plateau boundary. The northern portion of the area is occupied by the southernmost part of Corbetta The Kobo Sub-basin where pressurized irrigation graben, which has a total length of about 90 kilometers. project is located between 12° 18' to 11° 56' N latitude It is known that the depressions in the rest of the area and 39° 23' to 39° 47' E longitudes. Administratively, it are also formed by smaller grabens. is located in the northern Wollo Zone of the Amhara International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 08, No. 03, June, 2015, pp. 36-46 38 Groundwater Management for Irrigation in the Raya and Kobo Valleys, Northern Ethiopia The geology of the area is made up predominantly of Kobo Valley basaltic rocks occurring in the graben shoulders and The most important aquifer in the valley is the plain beyond and superficial deposits on the graben floors. unconfined sediments. The eastern and western acidic Other rocks such as rhyolite, small granitic intrusions volcanic rocks and the inselberg hills within the plain and sandstone do also occur. are almost impermeable. 1.2.3. Hydrogeology The Kobo plain is a flat plain with decreasing slope Raya Valley from west toward east and it is filled with Quaternary alluvial deposits derived from the surrounding basaltic The valley floor is bounded on both west and the east mountain range. The alluvial deposits are composed of directions by highly fractured and weathered basaltic intercalating layers of gravel, sand, silt and clay. Both rocks, mainly Ashangi basalt. A groundwater resource geophysical investigation and drilled well logs indicate is believed to be the huge water resource in the area. thickness of the sediment aquifer ranges from few The dominant groundwater flow directions are north- meters to 170 meters. The thickness is minimal on both south and west-east. The depth of groundwater varies western and eastern flanks whereas the maximum of from about 20 m in Waja and Adis-Kigni (south) areas 250 m, occurs towards the central part.