POSSIBILITIES OF ASSESSING THE FLOOD RUNOFF PROBABILITY IN ANGARA REGION (IYA RIVER AS EXAMPLE)
This work aim is analyzing the flood hazard in the Angara region with using stochastic hydrology methods. This region is characterized by greatest danger of summer rain floods, relatively rare but systematic, and are very dangerous. The possibility is studied to construct one-dimensional analytical distribution curves that reliably approximates a series of observed maximum annual discharges and allow to give a reasonable estimate of the extreme floods probability – using the example of extraordinary floods on the Iya River in 1984 and 2019. A number of three-parameter probability laws and methods of probability curves parameterization was used.
Resulting, 14 variants of analytical distribution curves were constructed, compared by the statistical and rational criteria. Despite the several versions satisfy to almost all the requirements, it seems impossible to solve the problem qualitatively on their basis. All acceptable curve versions underestimate the probability for extraordinary floods of 1984 and 2019 years. Some of these versions go beyond the
5-95% confidence intervals of empirical probability curve, or are the results of direct mathematical fitting without the satisfactory conceptual reasons.
Thus, it was not possible to construct adequate three-parameter maximum discharge distribution for the Iya River according to above requirements. The complexity of the runoff formation processes in the region, different generation mechanisms of ordinary and extraordinary floods, obviously, leads to statistical heterogeneity of the series, which cannot be correctly described by one-dimensional three-parameter distribution laws. To assess the extraordinary floods probability, it seems most appropriate to use dynamic-stochastic modeling based on a physically based runoff model
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