ASSESSMENT OF WATER HARVESTING TECHNOLOGY  EFFECT ON DOWNSTREAM WATER AVAILABILITY USING  (CASE OF ALABA SPECIAL WOREDA, ETHIOPIA. ASSESSMENT OF WATER HARVESTING TECHNOLOGY  EFFECT ON DOWNSTREAM WATER AVAILABILITY USING  SWAT MODEL,  CASE OF ALABA SPECIAL WOREDA, ETHIOPIA. ASSESSMENT OF WATER HARVESTING TECHNOLOGY  EFFECT ON DOWNSTREAM WATER AVAILABILITY USING  CASE OF ALABA SPECIAL WOREDA, ETHIOPIA.)
Creators: name: Ayalkibet Mekonnen
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2014

description: In hydrological cycle; there is many water-related  human interventions that modify the natural 
systems. Rainwater harvesting is one such intervention that involves harnessing of water in the 
upstream . Community level water harvesting technologies used in the upstream , that prevents 
the water runoff, it caused an impacts on downstream mainly disturbance on biodiversity and 
ecosystems.  The  main  objectives  of  the  study  is  assessing  the  effects  of  water  harvesting 
technologies on downstream  water  availability  in  Alaba  Special Woreda,  to address  the above 
problem.  The  methods   used  include  a  secondary  and  primary  data  on  SWAT  model,  Cost
Benefit Ratio and Optimal control methods to analysiz the hydrological impact , Socioeconomic 
impact  and  tradeoff  of  on  upstream  and  downstream  water  availability  of  the  community 
respectively.  The downstream impacts of increasing water consumption in the upstream rain-fed 
areas of the Bilate and Shala Catchment are simulated using the semi-distributed SWAT model. 
The  two  land  use  scenarios  are  tested  at  subbasin  levels  (1)  conventional  land  use  which 
represents  the  current  land  use  practice  in  the  area  (Agri-CON)  and  (2)  in-field  rainwater 
harvesting (IRWH), improving soil water availability through rainwater harvesting. The model 
was manually calibrated from January 1997 to December 2002 the Nash and Sutcliffe efficiency 
index of 0.74 and r
2
of 0.75. The scenarios results were compared against the baseline period 
1989–2007.  The  simulated  water  balance  results  showed  that  the  highest  peak  mean  monthly 
direct flow was obtained on Agri-CON land use (12.71mm), followed by Agri-IRWH land use 
(11.5mm)  and  LULC  2005  (9.01mm).  The  Agri-IRWH  scenario  reduced  direct  flow  by  10% 
compared  to  Agri-CON  and  more  groundwater  flow  contributed  by  Agri-IRWH(19mm)  than 
Agri-CON(12.5mm).  Flow  reductions  are  comparatively  higher  in  the  upstream  parts  of  the 
basin,  as  a  result  of  a  relatively  higher  potential of  developing  rain-fed  areas  coupled  with 
comparatively lower amount of available runoff. Although there was a visible impact of the water 
harvesting technique on the water yield. The overall result suggests that the water yield of Alaba 
Special Woreda may not be adversely affected by the Agri-IRWH land use scenario despite its 
surface  runoff abstraction  design.  The  study  was  analyzed  costs-benefits  of  the  society.  The 
major costs include the initial construction cost of water harvesting system and the maintenance 
costs. The major benefits include an increase in household dispensable income, time and energy 
saved  from  collecting  water.  It  is  concluded  that  households  with  different  existing  water 
consumption  pattern  will  benefit  positively  in  investing  domestic  water  harvesting  systems 
having average Benefit Cost Ratio of 4.6 . I analyzed the tradeoff on Upstream and Downstream 
water  use  for  domestic  and  crop  production  .  With  the  optimal  control  approach  (OCA)  I 
identifed  the  economic  and  eco-logical  conditions  for  water  use  in  a  regime  where  a  social 
manager  controls  water  withdrawals.  Domestic  is  not optimal  that  the  value  of  the  water  per 
demand harvested is less than the amount of water needed to domestic purpose. Storage tanks, 
Series of check dams, gravel filled dams are an alternative solutions for water harvesting.