olume 4 No.12, December 2014 ISSN 2224-3577 International Journal of Science and Technology ©2014 IJST. All rights reserved http://www.ejournalofsciences.org Siltation of the Reservoir of Vea Irrigation Dam in the Bongo District of the Upper East Region, Ghana Thomas Apusiga Adongo 3 , Joseph Xorse Kugbe 1,2 , Vincent Danny Gbedzi 3 1 Department of Agronomy, University for Development Studies, Box TL 1882, Tamale, Ghana 2 Division of Ecology and Natural Resources Management, Center for Development Research, University of Bonn, Walter Flex Str. 3, D53113, Bonn, Germany 3 Department of Agricultural Mechanization and Irrigation Technology, University for Development Studies, Box TL 1882, Tamale, Ghana ABSTRACT The Vea Irrigation Dam was constructed in 1980 to promote the production of food crops in the dry harmattan season. Thirty three years after construction, this study was conducted to assess the level of siltation in the reservoir and farming practices that impacts siltation within the catchment. Ten soil profiles, five on either banks of the reservoir and each of surface dimensions 1.2 m x 1.2 m were dug in the reservoir 30 m away from the water to ascertain the depth of soil sediments. Average depth of sediments was multiplied by the area of reservoir to obtain the volume of deposited sediments, from which annual depositions were estimated. Eighty (80) farmers in the four fringe communities within the catchment (Vea, Gowrie, Kunkua, and Kuyelingo) were purposively sampled and interviewed. At an average depth of 1.1 m, total deposit of about 140000 m 3 of sediments into the reservoir should be a cause for concern. Conventional tillage and continuous grazing, practiced by majority of farmers along the steep slope of the dam’s upstream have direct influence on erosion and hence siltation of the reservoir. High intensity rainfall with high kinetic energies, recorded in the months of June, July, August and September results in considerable level of detachment of the already erodible soil aggregates, which contributes to erosion and subsequent siltation of the reservoir. Whilst vegetative cover reduces direct impact of rain drops, these are scanty and scattered: exposing the bare soil to erosion. In order to save the dam and its reservoir from short lifespan as a result of massive siltation, soil conservation measures, and Best Agricultural Management Practices on watersheds are recommended to local farmers within the catchment area. Keywords: Reservoir siltation, sediments, watershed, erosion, and irrigation. 1. INTRODUCTION A dam is an impervious or fairly impervious barrier, a hydraulic structure constructed across a natural river so that an artificial reservoir is formed on its up-stream side to store water [10]. In the rural and subsistence based northern Guinea Savannah zone of Ghana, dams are the main sources of water for watering cattle and for small-scale irrigation during the long harmattan dry season (November- March). They also provide water for watering of animals and for domestic activities [11]. Deposition of soil materials into dams reduces the capacity of the reservoir, impacting negatively on the shelf life of reservoirs and pose serious threats to livelihoods that depend on it. Excessive rates of sediment deposition in storage reservoirs, canals and laterals decrease the useful life of the dam’s project and increase the cost of maintenance [3]. Sediments found in irrigation water clog intake screens and pumps, fill channels, reduce reservoir capacity and useful life or deposit soil materials on crop lands [3]. Deposition of soil material into reservoirs come about through intense soil erosion, winning of sand and gravel, surface mining and other activities such as bush burning and deforestation. These render the soil surface bare to direct impact of rain. Intensive rainfall, coupled with large quantities of individual rainfall events, causes considerable runoff, which further lead to high sediment concentration in irrigation dams [12]. Bad farming methods such as farming closer to river banks, farming along the slope, and destruction of the vegetation cover contribute to the accelerated levels of particulate transport into reservoirs. The Vea Irrigation Dam is one of the oldest dams in the Upper East Region of Ghana. Constructed in 1980, it was aimed to promote irrigation farming during the dry season