RESERVOIRS WATER BALANCEANALYSIS, JOINT  OPERATION AND OPTIMAL OPERATION RULES  CURVE FOR SYSTEM PERFORMANCE  (A Case Study of Proposed Reservoirs on the  main Blue Nile River, Ethiopia)
Creators: name: Genet Ellala Abdissa
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2008

description: This study has been conducted on  the envisaged reservoirs along the main stem of  the 
Blue Nile River on Ethiopian highlands. The study sites  (i.e. Karadobi, Mandaya and 
Border reservoirs) water shed is located  in western part of Ethiopia, between 7° 45' and 
11° 12'50"N latitude, and 35°05'40" and  39°45'E longitude. Approximately all over 
basin here  is in after called Blue Nile River Basin (BNRB).See fig  1.1 
Management of available water resources and  its conservation in  terms of quantity and 
quality is necessary to  study the  source of water and appropriate method of utilization. 
This research has applied Spread sheet excel and HEC-ResSim technique to  determine 
the aspects of  reservoir water balance, monthly and daily reservoirs operation using 
Spread sheet and HEC-ResSim respectively in the case of proposed reservoir on the main 
Blue Nile in Ethiopia have calculated from  1972 to  2002. 
The spreadsheet model uses monthly evaporation,  surface runoff,  and precipitation as  an 
input and. groundwater component is neglected. Based on  the calculation results  it  is 
found that  evaporation, rainfall,  surface runoff inflow to  dam, regulated released, storages increments or declined and reservoir spillage from the reservoirs constitutes 46.40, 43.63, 
1505.81,  1185.13, 34.2 and 352.52 Mm3  of  the annual average Karadobi reservoirs water 
balance respectively, 38.50, 33.154, 2982.95, 2849.72, 244.79 and  183.22Mm3 
annual 
average for Mandaya reservoir and finally 51.26,' 41.89, 4198.66, 3855.65, 32.05 and 
306.86 Mm3  in case of annual average Border reservoir. Due to  the  climatic condition 
and  topography evaporation is the highest when we compare the relative volume-area of 
all reservoirs. The regulation of upstream reservoirs cause transference of flow pattern 
modification of  the downstream reservoir (i.e.  the regulation at Karadobi reservoir causes 
the  increment of flow during dry season by the volume of 190.22MCM and the reduction elevation curve to  calculate the head for power generation subsequently the mean power r 
are determined 2010.1, 1349.23, 740.57 MW from Karadobi, Mandaya and Border 
reservoirs respectively. 
Finally the HEC-ResSim model uses the reservoir physical characteristics (Elevation­ 
Capacity-Area curve), net monthly evaporation from the reservoirs  (mm), daily inflow 
(m3
/s) operation rule adjusted i.e. tandem operation for Karadobi and Mandaya reservoir 
finally released operation rule for  the Border reservoir,  the alternative released guide 
curve of elevation maximum capacity operation level and maximum elevation relation of 
dam appurtenant structures such as  spillway, penstocks and tail water elevation. The 
outputs of  tandem operation results an  operation rule based on  the reservoir water levels 
of  the three reservoirs that maximize the net release volume of water for  system 
maximum hydropower generation. HEC-ResSim has also used to determine the optimal release rule of  the maximum power generation by simulation/optimization technique, 
which is based on  successive trials. The analysis considered system power release pattern 
and  individual evaporation and spillage losses minimization and analysis optimal release 
alternative for  four different  system  levels for the maximum system conservative zone 
utilization up  to  90 percent. The advantages and disadvantages of  the other alternatives 
were evaluated. From the  released pattern alternatives,  the  simulation/ optimization 
operation was  suggested considering relatively the  system minimum  losses and maximum 
power generation of average 908.63,  1592.22 905.58 MW respectively in case of 
Karadobi, Mandaya and Border reservoirs respectively. These indicate the  intention of 
the optimal system performance