GIS Supported Irrigable  land and Water Resource Potential  Investigation tor  Irrigation  (The Case of Hare River Watershed)
Creators: name: ABEL TADESSE
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2005

description: Water  resources  development  and  utilization  is  usually  not  integrated  with 
Ethiopia's  overall  socio-economic  development  objectives.  In  the  above 
regard,  one  of  the  actions  included  in  the  strategy  encourages  to  undertake 
assessment  and  development  of  the  country's  surface  water  resources  by, 
among  others,  making  inventory of  the  available surface water  in  the  country 
both  in  quantity  and  quality  and  applying  suitable  methodologies  to  assess 
the available surface water both  in  time and space. 
As  integrated  development  of  water  resources  begin  with  an  inventory  of 
available  surface  water,  this  paper  in  particular  is  focusing  on  the 
investigation  of  availability  of  water  for  irrigation  by  implementing  modern 
tools  like  the Geographic  Information  System  (GIS) and Watershed  Modeling 
Software  (HEC-HMS) considering  the  Hare  river watershed  as  representative 
of the study. With  in  the  Hare watershed,  four  sub-basins  (namely  upper  Harrere,  Lower 
Harrere,  Gina  and  Lower  Hare) were  identified  for  these  study  based on the 
threshold  of  their contribution  to  flow.  The  flow which will  be  generated  from 
these  sub-basins will  be  one  set  of  decision  parameter weather  the  area  at 
the outlets of  the sub-basins can  benefit from  the  use of  irrigation. 
From  the  result  of  the  analysis  of  suitable  irrigable  land,  Lower  Hare  sub 
basin contributes  to most of the  irrigable  land  (about 63% of sub-basin extent) 
followed  by  the  Gina  sub-basin  (about  47%  of  sub-basin  extent).  The 
combined  lower  and  upper  Harrere  sub-basins  contribute  much  less  (about 
43%  of  combined  sub-basin  extent)  as  compared  to  the  separate  land 
contributed  by  the  other  two  sub-basins. As  a  result of  this  irrigation  demand 
assessment  focuses  primarily  on  crops  cultivated  on  the  Gina  and  Lower 
Hare Sub-basins. Assisted  by  the  CROPWAT  software,  the  requirements  of  the  different  crops 
in  the  respective  sub-basins were  made.  It was  observed  that  the  Gina  sub basin  doesn't  require  any sort of  diversion  from  the Gina River as  the  natural 
rainfall  is  sufficient  to  fulfill  the  crop  water  requirement while  the  scenario  is 
quite the opposite for the  lower Hare sub-basin. 
The  runoff  from  Gina,  Lower  Hare  and  Upper/Lower  Harrere  was  generated 
using  the  HEC-HMS  package.  The  runoff generated  from  the  upper two  sub­ 
basins  (i.e.  Gina  and  Harrere)  was  routed  through  to  the  outlets  at  Lower 
Hare.  It was  observed  that much  of  the  contribution  of  the  runoff at  the  lower 
Hare area comes from  the Gina sub-basin. Finally,  a  comparison  was  made  between  the  water  supply  from  the  main 
river  and  the  irrigation  water  demand with  in  the  adopted  frame  of  reference 
for  the  Lower  Hare  sub  basin  where  water  stress  is  obvious.  There  was  a 
deficit  zone  observed  in  the  period  of  analysis.  This  deficit  zone  during  the 
critical  crop  growth  stage  represents  more  than  55%  of  the  total  time  of 
analysis which  means  that  for more  than  half of  the  crop  duration,  the  crops 
are  subjected  to  water  stress.  This  result  was  helpful  to  conclude  that  this 
shortage  needs  to  be  compensated  by  means  of  irrigation  applications.  Also 
with  in  the  year  though  twice  harvesting  was  possible,  there  are  moments 
observed  where  water  stress  exists  and  need  to  be  compensated  if  desired 
crop production  level  is not meant to  reduce.