The Kronotskaya River is located on the east coast of Kamchatka, northeast of Petropavlovsk-on-Kamchatka. It is about 45 km long, with a total drop of 375 m. On its way from Kronotsky Lake to Kronotsky Bay, the river crosses two different areas both in relief and geological structure: in its upper reaches - the Eastern Volcanic Area, in its lower reaches - the Kronotsky coastal plain.

The All-Union Scientific and Technical Conference (Leningrad, 1957) on the design of dewatering measures on watered coal deposits noted significant successes in the design of dewatering measures associated with the relevant mining works. At the same time, the attention of scientific and technical community was fixed on a number of significant shortcomings related to the design of drainage works. For example, it was noted that the design of mining works is often conducted without taking into account the hydrogeological features of the field and the possibility of their drainage, so the design solutions for drainage are often complex. The methodology of hydrogeological calculations and obtaining initial design parameters for dewatering are still not sufficiently developed for complex hydrogeological conditions.

Some methods of calculating filtration from channels. In the design of trapezoidal-shaped channels, establishing the magnitude of water loss to filtration is essential. For unlined canals, to which the overwhelming majority of permanent and temporary irrigation canals belong, the question of loss values is usually related to determination of design flow rate under different operation modes. For canals intended for other purposes, which are in the stage of temporary operation before lining, the values of filtration losses play a well-known role in various calculations of hydraulic engineering works. Finally, at artificial ring matting of slopes and bottoms of unlined canals, the value of filtration loss is also used in relevant calculations.

Widespread use of the method of artificial lowering of the groundwater level in the construction of foundations for hydraulic and industrial structures, as well as large high-rise buildings caused the need to develop a methodology for calculating the water inflow to excavations in different hydrogeological conditions. The present article deals with the case of water inflow to the dewatering unit of an excavation, elongated in plan form, under the conditions of pressure-unpressurized regime of aquifers opened by the excavation. Attention to this case was attracted by the construction of a lock on a navigable canal. In spite of its special character, the set task is also of theoretical interest, as it allows us to check the suitability of certain calculation schemes and formulas in specific hydrogeological conditions. The excavation of the mentioned structure has already been realized at present, and the forecast of possible groundwater level lowering, which was given in 1952 when designing the structure on the basis of the calculations given below, was mostly confirmed.

In our work "Water inflow into a pit limited by a cofferdam" [3], we considered a case where the retaining horizon is supported by a watertight cofferdam, the base of which is flat and horizontal. Under these conditions, when inflowing into a pit limited by a cofferdam, the slopes of which are inclined to the horizon at an angle, the most significant quantities were determined when drawing up a production project and organizing work on the construction of a pit filtration inflow and the point of exit of the depression curve onto the slope of the pit.

Determining the possible water inflow is of significant practical interest in designing pits for structures or determining inflows to open mine workings, when the construction of pits or workings is associated with the opening of water-bearing confined strata. Existing methods for determining the filtration inflow in this case, as a rule, are aimed at most accurately establishing its specified value based on hydrogeological characteristics using hydraulic or hydromechanical methods. At the same time, the desire to establish the most accurate value of the filtration inflow is far from always justified for the following reasons. The value of the inflow is primarily of interest either when drawing up a project for the production and organization of excavation work, or when establishing the inflow to mine workings during the development of mineral deposits, when the ultimate goal is to establish drainage methods, the number and performance of the required pumps, energy requirements, etc. Experience in designing construction work shows that the filtration inflow can be established with an accuracy of up to several cubic meters per hour, which provides sufficient opportunity to determine the necessary drainage facilities. Thus, the approximate value of the filtration inflow for the above purposes can be considered acceptable.

In the practice of hydraulic engineering, one often encounters the following case of water inflow into a pit limited by a cofferdam. The pit is arranged in loose, practically homogeneous rocks, characterized by a constant filtration coefficient. Its bottom coincides with the aquiclude, the slope is determined by a certain slope coefficient m = ctg φ, constant along the entire height. The pit is limited by a cofferdam, composed of rocks, the filtration coefficient of which is very small compared to the filtration coefficient of the soils underlying the cofferdam. The cofferdam maintains a certain level in the upper pool. Water from the pool moves under the cofferdam and comes out onto the pit slope. In this case, in practice, the most common case is when, upon reaching the slope at point M, the underground flow is characterized as unconfined. At the same time, in the initial section of its movement under the cofferdam, the underground flow, limited from above by the base of the cofferdam and from below by the aquiclude, is under pressure.

Hydraulic engineering urgently requires the most complete and in-depth development of certain scientific and technical problems for the purpose of a correct quantitative and qualitative assessment of the movement of groundwater both in natural conditions and in conditions created as a result of an artificial change in the movement regime. Of these problems, the question of the movement of groundwater in artesian strata is of significant interest. Note that while the theory of the movement of underground gravity flows and its practical application have been developed in great detail and were set out with sufficient completeness by Academician N. N. Pavlovskii in his well-known work "Uneven Movement of Groundwater", movement in artesian strata has been studied extremely poorly and very little attention has been and is being paid to this issue. When designing hydraulic structures and reservoirs, when analyzing the regime of groundwater, as well as in many other cases, it is often necessary to give a technical assessment of the movement in artesian strata.