In case of pumping from a pressurized aquifer at a dynamic water level located above its roof, during the period of unsteady water inflow to the borehole, the pumped water is obtained at the expense of “elastic reserve” (an aquifer not communicating with other aquifers or surface water bodies within the area of the depression funnel). “Elastic reserve”, according to V.N. Shchelkachev, is the volume of water displaced into the well during elastic expansion of water and water-bearing rocks due to pressure drop in the depression area.

Absorption of washing fluid is a clear sign of water permeability of rocks passed by boreholes. It is especially important to take into account the absorption of flushing fluid by fractured and karsted rocks, where the absorption of even clay solutions is often significant and can be used for preliminary judgment of the water permeability of these rocks (before the production of experimental hydrogeological work).

Calculations of filtration coefficient and radius of influence according to the data of experimental pad pumping are usually made by Dupuis formula. The calculation is performed separately for each pair of observation wells, then the average of the obtained results is determined or the most acceptable value of the filtration coefficient and radius of influence is accepted. Discrepancies between the values obtained by parallel calculations for different pairs of observation wells depend on: 1) the degree of homogeneity of water-bearing rocks; 2) the quality of the experimental work carried out; 3) deviations in the direction of groundwater movement during pumping corresponding to a strictly radial flow. Often, especially in fractured rocks, these discrepancies are significant, and the average of individual obtained values of water permeability coefficient or radius of influence may differ significantly from the true value.

Turbulent movement of groundwater is known to occur at significant cross-sections of water-conducting channels in rocks and sufficiently high groundwater velocities and gradients. More often the development of turbulent movement is observed in fractured rocks intersected by open fractures with a significant gap and in karsted rocks. In loose porous rocks, turbulent motion occurs only in highly permeable rocks such as pebbles and gravel-pebble formations, and the filtration rates and gradients at which the development of turbulent motion begins in these rocks are much higher than in fractured and karsted rocks. At present, as a result of a number of research works carried out in laboratory and field conditions, it has been established that laminar movement of groundwater often takes place in fractured and even karsted rocks. Therefore, for such rocks it is possible to use the linear filtration law (Darcy's law) and dependencies based on this law under certain conditions. In particular, groundwater movement observed in natural conditions is characterized by small hydraulic gradients and usually obeys the linear law, even in rocks intersected by large open fractures and often in karsted rocks.

The issue of the influence of the specific gravity of groundwater on the conditions of its occurrence and movement is rather poorly covered in the literature. When studying fresh and slightly mineralized waters, their specific gravity is usually taken to be equal to 1, neglecting its minor changes depending on temperature, pressure and concentration of dissolved substances. However, when studying waters of increased mineralization (approximately starting with a total mineralization of 5-10 g / l) and especially brines, the increased specific gravity of water so strongly modifies the hydrodynamic conditions and affects the water level in wells (data used to determine the direction and speed of movement of groundwater), that conventional methods of calculations and constructions lead to gross errors and even complete distortion of reality. It is known that the presence of water of increased specific gravity in boreholes (caused by high mineralization or the content of suspended particles) leads to a decrease in the water levels in them, and to calculate the level corresponding to fresh clean water ("reduced level"), the following are introduced simple corrections. However, these corrections are still insufficient for calculating the movement of groundwater, which requires a significant modification of the usual filtration equations. The most difficult issue is determining the conditions of equilibrium, as well as the direction and speed of movement of groundwater with their variable specific gravity, especially when the specific gravity changes in the vertical and horizontal directions, which is usually observed in nature.

Issues related to the movement of groundwater in fractured rocks have been poorly covered in literature to date. Hydrogeology manuals only provide a diagram of water movement through fractures, proposed back in 1912 by A. A. Krasnopolskii, which provides for a turbulent flow regime expressed by Chezy's law. Meanwhile, there are currently calculated and experimental data that allow for a more complete coverage of the conditions of water movement in fractured rocks, which may be of significant practical importance. In this short article, the author presents his hydraulic calculations based on an examination of the simplest model of fractured rock, taking into account the available experimental materials. As a result, conclusions were drawn regarding the water movement regime in fractured rocks and the dependence of their permeability on the size and density of the fractures.