Steady State Groundwater flow Modelling of the Sunuta Catchment (Western Afar Region): Special Emphasis on Effect of Groundwater Pumping for Irrigation

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Addis Ababa University


The study area is situated in the lower Awash basin, with in zone four of Afar National Regional State and Northern Wollo zone of Amhara Regional state. Sunuta plain is located about 690km Northeast of Addis Ababa. The total study catchment area is 1870km2 of which 1476 km2 belongs to Sunuta plain (rift floor/ lowlands) and 394 km2 belongs to the mountainous area (rift escarpments and highlands). In sunuta catchment there are more than 69 boreholes drilled so far for groundwater-based irrigation and water supply purpose. Currently the groundwater abstraction rate is 26,047.80m3/day. However, in the study area there is no significant research conducted so far to know the groundwater resources. The main objective of the research is steady state numerical groundwater modeling of sunuta catchment to evaluate the impact of current and projected pumping on the groundwater system. Groundwater recharge in the study area is estimated using WetSpass modeling method. The estimated recharge result was 61.1mm/year. The mathematical code Processing MODFLOW Pm8 software is applied in the study area for steady state conditions. The model is horizontally discretized with regular grid spacing of 300m by 300m having 147 rows and 283 columns and one layer having 250m thickness. The layer type is confined/unconfined transmissivity variable. Model calibration is carried out by manual trial and error adjustments of the parameters until the value of simulated and observed result is within the acceptable error. The simulated recharge of the model domain is 50.2mm/year which is close to the estimated recharge using WetSpass model and lateral groundwater flow within certain cross-sectional area using Darcy’s approach methods. The current abstraction rate of the area is 26,047.80m3/day which accounts 10.1% of the simulated recharge. And pumping scenario for steady state model are scenario- one (69 boreholes are operated simultaneously) and scenario-two (91 wells are operated simultaneously) indicate respective groundwater abstraction of 92,039.04 m3/day and 128,759.04 m3/day. This resulted in an average groundwater level decline of about 27m and 41m respectively.



Sunuta Catchment, Recharge, Abstraction, Groundwater Modeling