Principles of estimating soil moisture parameters in a river basin
DOI:
https://doi.org/10.31861/geo.2025.854.232-240Keywords:
infiltration,, particle-size distribution,, Carpathian-Podilia region,, soil moisture,, porosity,, filtration coefficient.Abstract
The paper examines the physical and mathematical principles governing soil moisture formation and the transformation of precipitation into components of river runoff within the river basins of the Carpathian-Podillia region. A central role in the study is assigned to the soil profile as the leading element of the vertical structure of a catchment, which performs the functions of moisture accumulation, redistribution, and loss during the formation of rainfall floods and low-flow conditions. It is demonstrated that soil properties-namely granulometric composition, porosity, water-holding capacity, and the filtration coefficient-determine the intensity and relative contributions of infiltration, subsurface flow, surface runoff, and evaporation.
The relevance of the study is driven by the increasing frequency of extreme hydrometeorological events, the need to improve the accuracy of short-term flood forecasting, and the necessity to refine runoff formation models under conditions of pronounced spatial heterogeneity of soil and landscape characteristics. The current state of scientific research on soil water movement modeling is analyzed, including the contributions of both national and international scholars who established the theoretical and methodological foundations for studying infiltration, subsurface flow, and evaporation processes.
The paper generalizes approaches to the parameterization of slope runoff processes and flood hydrograph formation, taking into account slope geometry, the degree of convergence or divergence, and surface roughness. Analytical expressions describing water generation on slopes of different types are presented, and the role of slope constants and water generation intensity in forming inflow to the channel network is defined. Particular attention is paid to the active soil layer as a transformation chamber within which the main losses of slope runoff occur.
The vertical structure of the soil column is examined in detail, and at least three functional levels are distinguished: the near-surface layer, the active layer, and the zone of relative water retention transitioning to groundwater. It is shown that agrometeorological and agrophysical constants (wilting moisture content, minimum and maximum field capacity), together with the filtration coefficient, constitute the basic parameters for a quantitative description of soil water regime. Indirectly, these properties are reflected in the statistical characteristics of the spatio-temporal distribution of soil moisture.
Within the framework of the study, the dependence of the filtration coefficient on the granulometric and genetic composition of soils in eastern and western Podillia is analyzed. Generalized filtration coefficient curves are constructed for different genetic soil horizons, enabling the application of the obtained results in basin-scale runoff models at the regional level. It is established that the upper soil horizons (0-10 cm and 10-20 cm) are the most sensitive to moisture variability, whereas deeper layers respond to precipitation with a temporal delay.
Several methods for estimating evaporation are considered and compared, including the equation proposed by M.I. Budyko and modified relationships based on Dalton’s law. It is shown that evaporation coefficients are not constant values but vary depending on soil layer depth, current soil moisture content, and atmospheric moisture deficit. The results of calculations of the contribution of individual soil layers to evaporation losses during different time intervals of the vegetation period are presented.
The obtained results indicate that total evaporation from the soil column is formed as an integral effect of water losses from all its layers, while the contribution of deeper horizons increases as the near-surface layers dry out. An approach for estimating the relative contribution of individual computational soil layers to total evaporation is proposed, which can be applied in the development of physically based water balance models.
The practical significance of the study lies in the possibility of using the developed set of landscape-hydrological parameters to model various phases of river runoff, improve rainfall flood forecasting methods, and assess water resources of small and medium-sized river basins. The proposed approaches retain a high degree of universality and can be adapted to other physical and geographical conditions provided that an appropriate information base is available.
In summary, it is concluded that the temporal variability of soil moisture is governed by the interaction of two opposing processes-infiltration and evaporation-the intensity of which is controlled by soil properties and meteorological conditions. Accounting for these regularities is a necessary prerequisite for increasing the reliability of hydrological calculations and forecasts in the river basins of the Carpathian-Podillia region.
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