Calculation Approaches of the Probable Maximum Discharge of Spring Flood at Ungauged Sites in the Southern Buh River Basin, Ukraine

Abstract

Calculation of probable maximum discharge of spring flood are the great practical importance, since it is the basis to plan and design of different hydraulic structures, such as dams, culverts, urban and agriculture drainage systems, etc. Thus, the updating of the methodical approaches and parameters of the empirical formulas which using in the determining of the probable maximum discharge of spring flood at ungauged sites of the river basin is an actual task. In this paper for the Southern Buh River Basin were updated the parameters of the reduction formula and the limiting intensity formula of streamflow which are using to calculated of the probable maximum discharge of spring flood at ungauged basin in Ukraine. The presented results illustrate that parameters of empirical formulas that were calculated according to modern observation series (since the beginning of the observations to 2010) in comparison with previously received (since the beginning of the observations to 1980) have significant changes. We found out that it is due to cyclical of the long-term fluctuations of the maximum streamflow of spring flood in the Southern Buh River Basin. We also illustrated that for the small ungauged basins have the difficulties with the choice of rivers-analogues.

Spring flood frequency analysis in the Southern Buh River Basin, Ukraine

“…An analysis of the results shown that in the time series remained some gaps, but their percentage was significantly decreased (Table 2). In the Southern Buh River Basin there are difficulties with the choice of analogue rivers because observations do not cover small rivers and some tributaries (Gorbachova and Khrystyuk, 2018).…”

“…The last frequency analysis of observation data for the maximal discharges of spring floods of the Southern Buh River Basin was carried out in the paper of Gorbachova and Khrystyuk, 2018. In this paper, the calculation was carried out for the data to 2010 and were shown that values of maximal discharges of spring floods with 1% probability have the tendency to decrease in relation to the calculations which was completed according to the data to 1980. A comparative analysis of the results of this study with the results introduced in the paper of Gorbachova et al (2018) showed that the values of maximal discharges of spring floods with 1% probability as well as its statistical characteristics not significantly changed (Table 3,columns 6,7,8,and 10). Consequently, such a parameter as the mean values of maximal discharges of spring floods already became stable over time.…”

“…It is explained by the features of the maximal flow of spring floods of plain rivers, namely presence in the observation series only increasing and decreasing phases of cyclical fluctuations, their considerable duration, as well as the significant variability of maximal flow. Note: MLE -Maximum likelihood estimation method, MOM -Method of moments; in columns 6, 7, 8, and 10, the numerator shows the values that were calculated for the data to 2015, the denominator shows the values that were calculated for the data to 2010 (Gorbachova et al, 2018) The restoring of the gaps in the time series is especially important step in the investigation because it allowed obtaining information about extreme floods that were observed in the increasing phase of longterm cyclical fluctuations of the Southern Buh River Basin. It contributes to obtaining more reliable and stable over time of the statistical characteristics of time series.…”

“…Furthermore, such rivers almost do not have an underground supply and in the summer-autumn period it dries up. In winter period, such rivers are usually frozen (Gorbachova and Khrystyuk, 2018). Southern Buh River basin is characterized by a clearly pronounced spring flood, during which it is forming from 35 to 60% of annual streamflow (Shakirzanova, 2015).…”