Nátok

Nátok is a hydrological term used to describe the inflow of water into a body of water or a hydrological system. It denotes the total amount of water entering per unit time, typically expressed in cubic meters per second (m3/s) or as a volume over a given period. In a lake or reservoir, nátok includes surface inflow from tributaries, groundwater discharge (baseflow) into the water body, and, depending on definition, direct precipitation onto the water surface and runoff from the watershed.

In hydrological modelling, nátok is a key component of the water balance, alongside outflow (odtok) and changes in storage. Its magnitude and timing influence water level fluctuations, water quality, and ecological conditions. The term is often used when assessing lake or reservoir governance, flood forecasting, and nutrient or sediment transport studies.

Measurement and estimation: nátok is estimated through a combination of gauged inflows, groundwater assessments, and hydrological modelling. Methods include direct flow measurements at inflowing streams, discharge measurements, and water-balance approaches that allocate precipitation, runoff, and groundwater contributions to the inflow. Temporal variability is common, with higher inflows during spring snowmelt or after heavy rainfall and lower inflows in dry periods.

See also: odtok (outflow), water balance, discharge, hydrograph. The concept is widely used in Slovak hydrology and in international contexts with similar terminology for inflow into water bodies.