Groundwater Modeling and Optimization of Irrigation
Water Use Efficiency to sustain Irrigation in Kobo Valley,
Ethiopia
Getahun Wendmkun Adane
March 13,2014
Introduction and Rationale
Location: Northern Eastern Amhara regional state, Ethiopia

rich in fertile soil and has a potential of over 10,000ha of land to irrigate.
 Groundwater is the main source & irrigation is the main sector.
 Recharge
 Abstraction of Groundwater and Pumping scenarios.
 On-farm water management and Irrigation water use efficiency
A1. Introduction to IWRM
Major Problems
• Low and erratic rainfall distribution limits production & food security.
• Absence of scientific and local groundwater resource management is
the main factor for sustainable use of ground water.
• Due to poor on-farm water management, there is excessive use and
this leads to high energy cost.
1400.00
kobo annual rainfall (1996-2010)
Annual precipitation (mm)
kobo
1200.00
1000.00
800.00
600.00
400.00
200.00
0.00
Time in Years
A1. Introduction to IWRM
Key Research Questions
• What is the recharge and abstraction of groundwater in the study
area?
• What are the impacts or drawdown of wells under different well
operation scenarios?
• How does on-farm water management will be successful to improve
irrigation efficiency?
A1. Introduction to IWRM
Research Methodology
A1. Introduction to IWRM
Field work activities
Major findings
• Total recharge is calculated using water balance and Darcy’s approach (94.8MCM &
82.6MCM respectively)
• Model simulated total recharge is resulted in 117.9MCM
• The water budget of the model domain indicates that the valley gets more recharge
from horizontal flux(79.9MCM) than other recharge sources.
• Model calibration evaluation shows that the simulated head matches reasonably the
observed head with RMSE of 6.63m.
• The contour map of the simulated heads is in agreement with the flow direction of
conceptual model.
• The model was run for two pumping scenarios. Hence a total of 2.79 x104m3d-1 and
5.58 x104m3d-1 abstracted water resulted in an average decline of groundwater level
by 14m and 32m respectively.
• Groundwater reserve was calculated as 1206MCM for HG &1190MCM for WG basins.
• Allowable exploitable amount of water was also estimated as 714MCM for HG &
724MCM for WG sub-basins so as to propose additional wells of 78 & 75 respectively.
A1. Introduction to IWRM
Major findings
• Comparison b/n observed & simulated head of different scenarios.
• The Aqua crop model predicts the irrigation water demand of 404mm for maize but
the existing condition uses 730mm of irrigation water pumped from a well of 50l/s
average discharge to irrigate an average of 45 ha of land with less production.
A1. Introduction to IWRM
Pumping scenarios
• Scenario-one
scenario-two
Conclusions
• The field observation together with the simulated output can be used to realize the
aquifer systems of the valley under steady state condition.
• The calibrated model was able to reasonably simulate the hydraulic heads that match
the observed head with out changing the general hydraulic gradient of the valley.
• Groundwater abstractions under scenario-one and two resulted in a maximum
groundwater decline of about 26m & 45m respectively at well HG8,which currently has
a discharge of 26l/s from 50 l/s.
• The calibrated model simulated water budget shows that the valley gets more inflow
from high lands through horizontal flux.
• The Aqua crop model simulation results clearly indicate how to improve on-farm water
management and optimize water use efficiency with a good production.
• Additional wells of 78 for Hormat -Golina and 75 for Waja-Golesha sub –basins is
proposed keeping the minimum radius influence of 250m based on the allowable
exploitable water.
A1. Introduction to IWRM
Recommendations
• Optimum operation of wells ( up to 35 wells) at a time is recommended keeping the
minimum distance between two closer wells at 500m.
• The output from this study can be used as a starting point for transient state
groundwater modelling for better predictions of pumping effect and for better
recharge simulation
• Interested professionals can use MODFLOW for similar areas of interest.
• Careful attention should be taken regarding the use of pesticides, and over fertilizing
that causes groundwater contaminations.
• Artificial recharge and water shad-management practices should be enhanced to
increase the natural recharge.
• Regular monitoring of groundwater level in wells is recommended so as to understand
the variations in time for groundwater heads.
• River gauging & meteorological stations should be installed in order to improve data
availability and better understanding of the sub-basins water balance.
A1. Introduction to IWRM
Thank you