Vol 5 No 1 (2018)
Articles

Water Balance Model: Implications for Groundwater Recharge Estimation in Data Scarce Arid Catchment, Northern Ethiopia

Nata T. Tafesse
Department of Geology, University of Botswana
Michiele Gebrehiwet
Department of Land Resources Management and Environmental Protection, Mekelle University
Solomon Habtu
Department of Land Resources Management and Environmental Protection, Mekelle University
Berhanu F. Alemaw
Department of Geology, University of Botswana
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Keywords
  • Command area,
  • Evapotranspiration,
  • Recharge,
  • Reservoir,
  • Runoff.

Abstract

The paper presents results related to water balance model of the Gumselassa catchment (28.1 km2), Tigray, Northern Ethiopia. The catchment includes a small dam called Gumselassa dam having an effective watershed area of 22.14 km2 with reservoir capacity of 1.92 x 106 m3 and command area of about 1sq. km. The hydrology of the area was characterized on the basis of land use, soil, slope and climatic parameters. Different methods were employed in this study: rainfall coefficient method was used to determine monthly distribution of rainfall; Penman method to calculate evaporation from the reservoir; Thornthwaite method and Thornthwaite water balance model to determine potential and actual evapotranspiration; runoff coefficient method to estimate runoff; and, the water balance model was used to quantify the recharge. The catchment is characterized by one rainy season (three months) and two dry seasons (nine months) during the year. The mean annual rainfall of the catchment is 485.89 mm. The total annual water loss by evaporation from the reservoir is 1263.27 mm. The mean annual actual evapotranspiration of the effective watershed area one and two is 318.57 mm and 310.27 mm, respectively. The mean annual actual evapotranspiration of the water contributing area 1 and 2 to the command area is 337.06 mm and 355.29 mm, respectively. The mean annual actual evapotranspiration of the command area is 319.3 mm. The mean annual runoff generated from the effective watershed area one and two is 1.167 and 0.44 million cubic meters, respectively. The mean annual runoff generated from the water contributing area 1 and 2 to the command area is 0.048 and 0.349 million cubic meters, respectively. The mean annual runoff generated from the command area is 0.0875 million cubic meters. The total amount of water which is actually available to recharge the groundwater within the catchment is 4.065 million cubic meters, and any application of water for irrigation from the reservoir should take into account this readily available water.

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