Downstream hydraulic geometry relations for the rivers of Tomsk region

Use of downstream hydraulic geometry relations receives increasing attention.Such kind of relations enables to predict the future condition of the rivers and, in particular, characteristics of their channel morphology.Thus, they enable both qualitative and quantitative representation of stream and bed morphology reaction to the influences ofdifferent character. Five lowland rivers of Tomsk region (in the south-east periphery of the West Siberian Plain) with sand and gravelbeds were chosen for the study; and the data on 633 cross-sections were assembled. The purpose of the study is the establishment ofdownstream hydraulic geometry relations for the chosen rivers of different size. As the initial data, the values of bankfull water dischargeon the study reach and the corresponding values of hydraulic parameters of channels and streamflows have been indicated. Thelatter have been received by means of modelling of the appropriate fragments of channel network in the program НEC-RAS 3.2. Whilederiving downstream hydraulic geometry relations of the required kind, non-linear regression analysis of available data has been madeon the basis of general linear model of multiple regression as a power law relation between the width, average depth and velocity of theriver and its slope, average sediment particle size and the Shields parameter, related to the bankfull water discharge. As a result, theequations providing sufficient accuracy of approximation confirmed by high value of the determination coefficient have been derived.Moreover, on the basis of the data assembled some computations have been implemented using similar formulas derived by differentauthors for different regions and datasets. The formulas offered in our study provide better accuracy of computation of such characteristicsas the water slope and Shields parameter for the rivers studied. Similar formulas of other authors give systematic errors of calculationof these characteristics for our rivers. Possible causes of the bias are discussed. Accuracy of computation of such parameters as theaverage width, depth and flow velocity using our formulas and formulas of different authors are approximately comparable. The formulaspresented in the article may be applied to the rivers Ob, Tom and small rivers of Tomsk region for solving the problems of hydraulicdesign and construction, clearing river channels and for other measures for water regime control.

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