Getahun Wendmkun Adane March 13,2014 Groundwater Modeling and Optimization of Irrigation Water Use Efficiency to sustain Irrigation in Kobo Valley, Ethiopia

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. 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 x10 4 m 3 d -1 and 5.58 x10 4 m 3 d -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

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