KARUN3 PROBABLE MAXIMUM FLOOD (PMF) REVISION & ITS EFFECT ON FLOOD DISCHARGE SYSTEM and INCREASING HYDROPOWER GENERATION

PMP is the most important parameters that usually would be applied in PMF.Its calculated by statistic or maximization of involved terms methods. But lack of sufficient data causes it to be used with other methods (i.e., Paleo-Flood…) preferably. In 1984, Acres/LWRD through Karun3 feasibility study achieved PMP by 432mm and PMF by 27'900cms based on 1980 storm data. In 1991 Mahab-Acres G.P. proposed 22'350cms with considering new simulation assumption. This modification caused a lot of change in dam spillway orientation layout and decreased the project cost. Mahab, in 1999 reached to 464mm for PMP used the recent 6'230cms flood record to attain 21'900cms for PMF.The most important result was to remove one bay of chute spillway. In a report that was issued by Mahab-Acres (MGA) in 2001, that was proposed an 18'650cms PMF but MGA define a 17'000 to 26'000cms range consequently. Finally; it was adopted 19'000cms for PMF peak. As its result, the owner (IWPC) made benefit by removing two orifice spillway. An investigation on in plan dams and under construction on Karun river indicated unconformity in estimating PMF.Therefore,IWPC ,the main owner of hydro-power project in Iran made decision to make a conformity here for the chained dams design flood. In this regard, the Karun river dams down to Gotvand PMP & PMF study devolved to Mahab- Ghodss collaborating with some experienced professors. As its result that reported in 2003, PMF was reduced again to 15'500cms and the owner could eliminate two bays of crest spillway consequently. It should be noted that these modified shape helped considerably to structural design of plunge pool. It became possible to heighten the Normal Water Level by 5 meters to increase power generation accordingly. In this study PMF was estimated by synoptic method and run off-rainfall model by dividing basin to several sub basins. We could conclude by this paper, that the procedure of estimating Karun3 PMF were carried out over the past 20 years states too difference between 15'000 to 28'000cms and unconformity in analysis methods. So, adopting PMF as a design flood basically could be sensitive, uncertain and some doubtable because it would be impossible to converge all viewpoints and clearly, it could have so much negative effects on project time schedule & cost. According to numerous under construction & in plan dams in country it's proposed for complementary assessment for optimizing estimation of PMF based on economical conditions and development policy.