The term of river channel-forming water discharge is widely used for characterization of the influence of a stream on its channel experiencing deformations. Many different interpretations of this term exist and many measures of channel-forming discharge are most commonly applied: channel-forming discharge determined using a technique proposed by N.I. Makkaveev, bankfull discharge, and discharges of different frequencies/durations and probabilities of exceedance. Authors consider all these interpretations as characteristic discharges. The study purpose is determination of characteristic discharges causing the most intensive influence on the channel-forming processes in lowland rivers of the southeast of the West Siberian plain. As initial information we use long-term discharge observations at nine reference gauge stations on six rivers of Tomsk region: the Ob at Kolpashevo, the Tom at Tomsk, the Chulym at Teguldet, Ziryanskoe, Sergeevo and Kommunarka, the Vasyugan at Sredniy Vasyugan, Chaya at Podgornoe, and the Iksa at Plotnikovo. The applied methods include the Makkaveevs technique for estimations of Qf, techniques for determination of bankfull discharge Qbf , and statistical techniques for discharge frequency and probability of discharge exceedance calculation. For all stations the values of channel-forming discharges Qf corresponding to some of three specific intervals have been determined and their dependences on the period of time shown. In order to simplify the estimation of Qf for ungauged rivers bankfull discharges Qf for nine reference stations were determined. Comparison of bankfull Qbf and channel-forming discharges Qf of the middle interval allows concluding that the former provide means for precise estimations of the latter. Our study has also shown that the duration (or frequency) of the middle interval Qf varies between 2.33 and 5.54% while the duration of the lower interval Qf changes between 17.1 and 35.8 %, so it is possible to make estimations of the middle and lower interval Qf using these values of duration. On the contrary, the probabilities of exceedance of annual maximum and annual mean discharges related to values of the upper interval and middle interval discharges Qf, respectively, are different for different river stations and their use for determination of Qf did not prove to be so successful. Nevertheless, the values of frequencies/durations and probabilities of exceedance could provide alternative means for the determination of channel-forming discharges for ungauged rivers.

Работа посвящена исследованию условий процесса руслоформирования равнинных рек разной величины, протекающих в Томской области. Определены характерные расходы воды, влияние которых на русло является наиболее интенсивным. При определении этих расходов применялся метод Н.И. Маккавеева, методы оценки руслонаполняющих расходов и методы статистической обработки гидрологической информации. Прослежена динамика изменения значений руслоформирующих расходов воды во времени. Определены соотношения характерных расходов воды между собой. Установлена тесная связь между руслоформирующими расходами воды среднего интервала и руслонаполняющими расходами воды, подтвержденная высоким значением коэффициента детерминации.