Scientific and methodological base for calculation of rain and spring floods maximum runoff

Abstract

For more than 40 years estimated characteristics of rivers' maximum runoff for rain and spring floods in Ukraine have been determined using the regulatory document SNiP 2.01.14-83. This regulatory document is based on use of reduction formulas (for spring floods, rain floods with catchment areas of F >200 km2) and maximum intensity formulas (for rain floods with catchment areas of F < 200 km2). Use of reduction structure for rain and spring floods of different reduction have no relevant grounds since in both cases we deal with calculation of maximum water discharge forming the part of unimodular hydrographs. In addition, a calculated parameter of "friendliness" k0 is determined for spring floods by use of hydrological analogues, which, by the way, are assigned rather provisionally. Regarding rain floods the impact in the form of coefficients of analogy is replaced by the runoff module q200 taken for a provisional catchment area F = 200 km2. In methodological terms, in contrast to the "friendliness" coefficient of the spring flood k0 determined by the method of hydrological analogy, module q200 (for rain floods) is represented by a map of isolines. More remarks can be voiced with regard to the methodological base of determination of maximum modules of rain floods runoff within small catchment areas (F <200 km2). The main drawback relating to the use of maximum intensity formula consists in the fact that natural process of transformation of rain floods “precipitation - slope inflow - river channel runoff” is replaced by the operator of "precipitation - river channel runoff". The authors of this article offer a universal approach to substantiation of the structure of the formula to determine the characteristics of maximum runoff of rain and spring floods. The original theoretical model for hydrographs of rain and spring floods is accepted as unimodular non-linear triangles. For the first time all the components of calculation equations of modules of maximum runoff of rain and spring floods are described by the same equations and differ only in numerical values of the parameters. The proposed scientific and methodological base for determination of modules of maximum runoff of rain and spring floods underwent practical test and is recommended for use when preparing a new Ukrainian regulatory document replacing SNiP 2.01.14-83.

Keywords

• maximum runoff, rain floods, spring floods, regulatory documents, runoff depth, reduction formulas, estimated water discharge