This chapter considered qualitatively different approaches to the water regime model of drained lands implementation. The fundamental difference of these approaches is that the regime forecast calculations on a long-term basis are performed for schematized natural reclamation conditions by typing meteorological regimes in the calculation periods of vegetation, appropriate schematization, and parameterization of water regulation of drained lands. Secondly, it is proposed in the framework of the balance equation to perform based on certain patterns, to calculate the process of water regime based on the relationship and interdependence of its elements at the boundaries and in connection with the process of redistribution of moisture within the active layer of soil in relation to its moisture content and storage capacity. Considered methods and models of water regime allow determining both potentially possible due to meteorological and agrotechnical conditions and effective values of irrigation norms in the development of design modes of irrigation by irrigation and subsoil at drained lands.
TopBackground
In general, at the territory of Ukraine and the Polesie zone, in the twentieth century there was a general tendency to increase air temperature and increase the amount of precipitation: the annual temperature increased by 0.3…0.7° C, and precipitation – by 50…100 mm, significantly (1,5 times) increased the frequency of significant anomalies of both indicators. Their intra-season variability has also increased.
According to all climate change scenarios, the amount of precipitation will also increase. In some seasons, this increase may exceed the existing level by 20% (Romashchenko, Rokochynsky, Halik et al., 2007). In the warm period of the year, as a result of a sharp rise in air temperature, much of the precipitation will be spent on evaporation. The main feature of the warming period is the constant uneven precipitation in the middle of the year and in some years.
At the same time, due to global warming, the zone of Polesie feels and will feel the greatest impact during the winter and spring seasons (Shawcroft, Lewon, Allen et al., 1974).
For drained areas with close groundwater, climatic conditions are directly involved in the formation of soil water regimes, both in the natural state and in certain technological periods of cultivation.
The projected increase in aridity in climate change (rising air temperatures, uneven distribution of rainfall in the warm season, inefficient accumulation of moisture in the soil, etc.), which are observed today, will inevitably lead to changes in the formation of water regime of drained lands agrolandscapes of the Polesie zone, in particular, due to the reduction of the natural moisture supply of the territory and the increase of potential evaporation and, accordingly, the total water consumption in the cultivation of crops on drained lands.
The shortage of natural moisture will require additional moisture for cultivated crops through the implementation of appropriate water regulation technologies on drained lands.
The direction and degree of impact on the natural water regime in the reclamation of excessively moist lands should meet the solution of the main task – to create through the implementation of hydromelioration measures a favorable regime of moisture of the active root layer of soil in compliance with environmental requirements.
When regulating the water regime of drained lands, there are mainly two often separate or periodically changing processes – drainage and wetting, which use interrelated, but at the same time independent principles and techniques of designing reclamation systems according to relevant technical solutions.
Drainage is intended to ensure the removal of excess water from wetlands during spring floods or rain floods. For this purpose, as a rule, hydrodynamic methods are used to calculate the movement of groundwater to drains (water intakes) and hydraulic calculations of parameters of drainage lines, canals, rivers, etc., which determine the position of groundwater level (GWL) in critical periods of wetting.
When reclamation of wetlands (overwet lands and periodically overwet lands), such periods are the most dangerous in the development of these lands for use in agricultural production, and hydrodynamic methods of calculating the movement of groundwater detail the regime of maximum allowable wetting of agricultural reclamation fields in these although very responsible, but relatively short periods. and floods.
Since the outlined issues form the basis of drainage reclamation, the appropriate methods of hydrodynamic and hydraulic calculations to determine the parameters of the regulatory and conductive network of drainage systems are currently developed for almost all major soil reclamation conditions at the appropriate scientific level, tested in practice. in the relevant special and regulatory and technical literature and we are not considered.
According to another, a much longer period of vegetation of cultivated crops on drained lands, soil moisture is determined by a much more complex set of factors that include meteorological, agrotechnical, soil reclamation, and other local conditions of water regime formation.
In this case, taking into account local hydrological characteristics and processes of formation of profitable and expendable elements of moisture exchange, which characterize the direction and intensity of both biological and geological cycles and, accordingly, the conditions of formation of water and general natural reclamation regimes of drained lands. due to the fact that they are mainly determined by the hydrometeorological regime of current conditions or typical (calculated in terms of humidity) growing seasons and can not be considered arbitrarily, regardless of natural conditions.