Impacts of Californian dams on flow regime and maximum/minimum flow probability distribution

摘要

Dams have major impacts on river hydrology with a general tendency to decrease annual maximumnflows and increase annual minimum flows. The analysis of 41 streamflow series in California, USA arenexamined, and the results show that, as expected, the mean values and variations of annual peak flowsnand maximum flows of different durations are reduced for almost all sites after dam use, and the largernthe ratio of total reservoir capacity to pre-dam annual runoff, the larger the rate of peak flow reduction.nHowever, the impacts on minimumflow are mixed. For five out of seven cases with long data records fornperiods before and after dam use, the average annual minimum flow as well as its variation increased,nbut for the other two cases, they decreased. No significant changes are detected for various extremenprecipitation indices; therefore, dam construction is believed to be the major reason for flow regimenchanges. The probability distribution of extreme flows also changed, due to the impacts of dams. ThenLog-Pearson Type III (LP3) distribution is best for peak flow series and one-day maximum series at sitesnwith or without the impact of dams; the three-parameter Weibull (W3) distribution is the best model fornthe seven-day minimum flow at sites with no or minor dam impacts, whereas at sites with major damnimpacts, the best model is the generalized extreme value (GEV) model for the seven-day minimum flow.