The Nineteenth Congress of the Communist Party of the Soviet Union, in its directives concerning the Fifth Five-Year Plan of the USSR for 1951-1955, set forth the ambitious task of harnessing the country's water resources. The construction of large hydroelectric power stations on the Volga and Dnieper Rivers, the development of the Ob, Angara, Irtysh, Kama, and other river systems, as well as drainage projects in regions such as the Polesie Marshes and the Baraba Lowland, placed important and challenging demands on the study of the nation's water resources. The complexity of the technical and scientific problems posed to hydrology by water conservancy construction practice makes it necessary to substantially improve the quality of professional hydrological training. To this end, special attention should be given to revealing the physical nature of the hydrological processes under study and of the methods used to solve practical problems. This situation makes it necessary to provide a comprehensive explanation of the issues addressed by modern land hydrology, especially various computational methods, since the correct application of these methods is possible only when the physical nature of the formation processes of the hydrological elements involved, as well as the scope of applicability of the calculation schemes used, are clearly understood. Accordingly, this textbook provides a special introduction to the theoretical foundations of distribution curves widely used in hydrological calculations, as well as the principles for constructing formulas for calculating maximum discharge in the absence of observational data. These topics are not necessarily included in the compulsory curriculum for secondary technical school students; however, the manner in which they are presented in this book allows them to serve effectively as supplementary material, helping readers gain a deeper understanding of the meaning and applicability of practical calculation methods. This book is the second edition of Hydrology and River Runoff, originally published in 1950, and has been extensively revised and expanded. Particular emphasis has been added to the analysis of flood formation processes, the development of methods for calculating maximum discharge under conditions lacking observational data, the fundamentals of mathematical statistics, river morphological characteristics, flow circulation, sediment transport, and related topics. The arrangement of chapters has also been adjusted in accordance with the sequence of study prescribed by the hydrometeorological technical school curriculum. The book makes extensive use of numerous new achievements obtained in recent years by Soviet scientists, particularly those of the State Hydrological Institute. The author adopted the recommendations of the reviewers and of the methodological committees of the hydrometeorological technical schools in Moscow and Kharkov, and also took into account the suggestions and constructive criticisms of the staff of the State Hydrological Institute. The author expresses sincere gratitude to all reviewers and to the personnel of the State Hydrological Institute, especially M. A. Velikanov, B. D. Zaikov, S. Yu. Belinkov, V. V. Ukhanov, and A. K. Prokudyakov, whose assistance contributed to the improvement of this book.