Groundwater Modeling and Optimization of Irrigation Water Use

Groundwater Modeling and Optimization of Irrigation
Water Use Efficiency to sustain Irrigation in Kobo Valley,
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.
kobo annual rainfall (1996-2010)
Annual precipitation (mm)
Time in Years
A1. Introduction to IWRM
Key Research Questions
• What is the recharge and abstraction of groundwater in the study
• 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
• 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
• 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

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