Aim of the study:
This paper presents the role and importance of the gravity-fed system for increasing the soil water resources and surface retention in sandy alluvial soils.

Material and methods:
The research was conducted on the Kopernia object (64.2 ha) within the Nida River Valley (Pińczów County, Świętokrzyskie Voivodeship) focused on the sub-irrigation systems formed in the second half of the 20th century. In order to identify the changes in soil water retention at the object, certain characteristics of soil profile were measure, such as gravitational water and volumetric water content in alluvial soil at different depths of groundwater table position. For determining surface retention the archival materials (technical project) as well as field tests e.g. ditch inventorisation, soil samples collection, were used. Additionally, in laboratory, the selected physical and water properties of alluvial soils were determined.

Results and conclusions:
On the basis of both the inventorisation of ditches and hydrotechnical constructions as well as field and laboratory tests, it was shown that during the proper operation of the irrigation system, water can be stored in the soil profile in the amount from 42 115.2 m3 to 62 916 m3, with 10 821 m3 of water in the ditches as a result of surface retention. Some of irrigation systems could be used to expand wetlands, also to increase small water retention. However, such changes would require large financial contributions and time to carry out these adjustments to current water policy and climate change.