TO THE QUESTION ABOUT CALCULATION OF DEBRIS-FLOWS DISCHARGE AND HIGHER DEBRIS-FLOWS HORIZONS OF 1% AND 5% REPEATABILITY
When performing engineering surveys, it is recommended to calculate the discharge and values of 1% and 5% of the debris-flows frequency. This frequency is calculated as 1% and 5% flow frequency of water discharge and flood water levels. Such calculations, in turn, are performed on the basis of calculations of 1% and 5% of the precipitation frequency falling. However, the debris-flows frequency does not always correspond to the water flow frequency. This is because the dominant role of the debris-flows process is played by geological factors of debris-flows formation. The occurrence of a debris-flow is preceded by a period of preparation of loose-rocks in debris-flows site (accumulation of a critical volume of loose-rocks and its achievement of a certain degree of moisture of loose-rocks) and the flood that caused the formation of a debris-flows in its parameters may be less than the flood. Equal in repeatability to with the corresponding accumulation of loose-rocks in debris-flows basin and strong soil moisture in potential debris-flows massif, the formation of debris-flows is caused by relatively small precipitation. For these reasons, the calculation of the frequency of debris-flows volumes and discharge on the basis of hydrological calculations only is unacceptable. When determining the frequency of the debris-flows maximum volumes and discharge, it is cannot to operate mechanically to compare the frequency of debris-flows and water discharge. There are no methods for calculating on the basis of geological factors the frequency of those parameters of debris-flow that determine the it’s volume. When designing objects and structures or when solving scientific problems, the use of the characteristic "5%, 1% of the debris-flows frequency" is unacceptable, since it leads to an unjustified underestimation of the degree of debris-flows hazard and to a wrong idea about debris-flows processes. All of the above fully applies to the provision of avalanches of large volumes.
Fleishman S.M. Seli. [Debris flow]. Leningrad, Gidrome-teoizdat, 1978. 312 p. (In Russian).
Kazakov N.A. Geologicheskie i landshaftnye kriterii ocenki lavinnoj i selevoj opasnosti pri stroitel'stve linejnyh sooruzhenij (na primere o. Sahalin). Avtoref. diss. kand. geol-min. najuk. [Geological and landscape criteria for assessing avalanche and debris flow hazard during the construction of linear structures (on the example of Sa-khalin Island). Ph. D. (geological and mineralogical) Thesis]. Yuzhno-Sahalinsk, 2000. 36 p. (In Russian).
Vinogradov Yu.B. Etyudy o selevykh potokakh [Etudes about mud stream]. Leningrad, Gidrometeoizdat Publ., 1980. 144 p. (in Russian).
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