Runoff formation in the small urban Setun river (Moscow)

The growth of the Moscow metropolis has led to profound changes in the hydrological processes of rivers located within the city limits. Based on 2019–2024 monitoring data for a network of stations on the Setun River, the river runoff formation in the context of urbanization was evaluated. The increase in impervious surface areas (from 25 % to almost 40 %) and the influence of industrial and municipal wastewater have led to the formation of specific water regime characterized by predominance of summer floods over the high water period, their large number (up to 29 events per year) and rather short basin lag time. Using the GrWat model, it was found that a twofold increase in residential areas and impervious surfaces downstream the river did not significantly affect the balance of river flow sources. The emerging water regime is characterized by an indistinct seasonal structure of the hydrograph and the transformation of the ground component of runoff into a technogenically transformed one, characterized by a greater volume of runoff compared to natural conditions. In different years and at different stations, it determines from 50 to 75 % of the annual runoff, while the spring floods account for 3,8 to 16,7 % and the rain runoff for 20 to 33 %. Compared to the second half of the 20th century, an increase of over 15 % in the residential areas (by 30 km2), as well as winter thaws, including those caused by regional climate change, determined a twofold decrease in water volume during spring floods, and almost tenfold increase in frequency of rainfall flood events. All this leads to frequent floods in river valleys and damage to city infrastructure, which makes the monitoring results very important for the city’s economy.