The numerator and denominator of Polish retention, or 15% of the outflow. Goal achieved!

Licznik i mianownik polskiej retencji

In Poland, it has been accepted that retention is primarily the construction of reservoirs, and small retention is the construction of small reservoirs. A few years ago, the issue was broadened to include the concept of trough retention, making weirs, water stages and thresholds also elements of low retention measures. This has allowed institutional water management to go far beyond the dozens of existing reservoirs and more than a dozen planned reservoirs and dams with funding. Adding the professional-sounding word “investment” to the mix, we are witnessing a situation where retention in Poland is set to increase, thanks to a large-scale technical commitment being carried out. It will mainly consist of construction, reconstruction, reconstruction and renovation. The goal of these measures is to achieve retention of the average annual outflow from Poland’s surface at 15%, as indicated by the Water Shortage Prevention Program developed by the Polish Water Authority[1]. But do we know what that means and how we go about it?

Water retention rates in Poland have been calculated for years, just as the goals that these values are supposed to meet have been determined. They make it possible to forecast what volume of water (non-)technical methods are capable of retaining in a catchment, and to indicate the amounts to which artificial or natural retention should aim. Their calculation usually involves relating the volume of retention (measured, for example, by the known capacity of retention reservoirs) to the rates of water available or flowing out of the Polish area.

The most commonly used denominator for this fraction is total river runoff. It can be determined from the sum of the average flows of all rivers flowing out of the Polish area at a given time (e.g., during the period of the year). However, it should be remembered that it must be reduced by the inflow of water into Poland. Some rivers, such as. This is because the Bug or Poprad flows into our country from the area of neighboring countries. This volume should not be considered in retention balancing. Similarly, the outflow from the Narew, for example, should not be counted, because the Vistula at the mouth, after all, carries the waters of its tributaries. Making such assumptions, based on data on the flows of Poland’s rivers, over the past 30 years, an average of about 47 km3 of water drains from the area of our country annually[2].

In determining the numerator of this fraction, however, a number of difficulties arise, mainly related to the lack of comprehensive data on the different types of retention. Taking the most conservative estimate of the retention volume of the dozens of largest reservoirs at 3,678 km3[3], we can in 2023. talk about their ability to retreat 7.8% of the outflow. This is 0.3% higher than current estimates by PGW Wody Polskie[4]. This amount is about 140 million cubic meters or two Siemianowka reservoirs, or, if you prefer, almost three times the usable retention of Lake Włocławek. The reservoir retention calculated in this way is, of course, only the easily recorded part of it. This is because we have many more retention reservoirs. Both those with a volume of more than 5 million cubic meters (this value is the contractual limit of small retention) and smaller ones. 2009 estimates. indicate that small retention in agriculture is at least 270 million m3[5]. Since then, however, there has been a lot of new investment in the sector, and it seems reasonable to adopt a conservative estimate of 300 million cubic meters of water retained. The State Forests, on the other hand, quantitatively summarizes the results of its retention activities[6] at about 42 million cubic meters. The entire volume of reservoir retention shown above thus already yields more than 8.5% of the average annual outflow from the Polish area. Supplementing these technical measures with the approximate volume of carp ponds (taking their surface area after Wojda and Zygmunt[7], at an equal 72,530 hectares at an average depth of 1 m), amounting to 725.3 million m3, we are exceeding – conservatively counting and not taking any investment measures – retention at 10% of the volume of average annual total outflow from the Polish area.

In addition to reservoir retention, we also have significant opportunities in Poland to regulate soil retention, if only in terms of proper water management on permanent grasslands. Not only for water retention purposes, but mainly to improve soil carbon content, reduce carbon dioxide emissions, and reduce subsidence of desiccated post-morph soils. The area of 1.8 million hectares of reclaimed permanent grassland, where we can raise the groundwater level using existing (or rapidly restorable) drainage infrastructure, assuming an average soil porosity of 0.8, offers the possibility of retaining an additional 1440 million m3 of water. This represents nearly three volumes of Lake Solina. It doesn’t stop there. To this retention should be added the weirs being built and repaired by the Regional Water Board on a massive scale in riverbeds. Even without a detailed calculation of the volume of artificially restored trough retention, we already have a level of 13% of the total runoff from the surface of our country. Adding the dammed lakes (288.61 million cubic meters of water[8]), we are thus already talking about 13.6%. And this is only artificial retention, achieved through technical measures. Taking into account all the omitted “medium” retention reservoirs, riverbed retention and soil retention on 4.7 million hectares of reclaimed arable land, one can venture to say that with the use of hydro-technical infrastructure we are currently retaining about 15% of the outflow in Poland, which is almost twice as much as the latest estimates of PGW Wody Polskie.

In light of the generally accurate estimates analyzed, one can venture to say that the 15% retention goal indicated in the Water Shortage Program[9] has already been achieved. So it’s time to declare this program a success and complete its implementation. The not inconsiderable funds saved in this way can be used to implement other equally technically and cost-intensive programs, such as the National Surface Water Restoration Program[10].

The primary goal facing Poland’s institutional water management, in terms of increasing water resources and improving retention, should now be the rapid implementation of river renaturalization measures widely proposed by the expert and scientific community (allowing to slow down groundwater drainage and improve self-purification of[11]), introduction of modern solutions for maintenance work[12] And peatland restoration. It is also worth taking into account the retention of beaver ponds in the retention balance. Indeed, these measures, in addition to the obvious benefits in terms of reducing runoff, provide a number of other benefits that have no alternative in any methods coming from the catalog of “hard” hydrotechnics. In terms of reducing carbon emissions from dry peatlands, we need to restore their proper hydration (not flooding!). In terms of reducing nutrient runoff, it is necessary to restore marshy buffer zones along all rivers and lake shores. This cannot be achieved by any measures of “classical” hydrology. In terms of increasing agricultural resilience to climate change, we need to start properly recording groundwater withdrawals. The use of the role of reservoirs and drainage systems should also be redefined. This is because today’s reality is different from the one at the time of their design and construction. Increased evaporation, snowless winters, nutrient supply and irregularity of precipitation challenge all the water and economic functions performed by reservoirs and drainage systems[13]. In terms of modern water engineering, we need an understanding that close to nature methods of reducing runoff and treating water are also retention. Moreover, these methods have no alternative, and their large-scale implementation in Poland is only – or as far as – a matter of time.

Matthew Grygoruk is a postdoctoral researcher in engineering and technology, a professor at the School of Agricultural Sciences. He works in the Department of Hydrology, Meteorology and Water Management at the Institute of Environmental Engineering of the Warsaw University of Life Sciences. He is involved in the study of hydrological processes in wetlands, the implementation of nature-based environmental management methods, and the valuation of aquatic and wetland ecosystem benefits. He is a member of the State Council for Environmental Protection, the Scientific Council at the Chief Inspectorate for Environmental Protection and the Scientific Council of the Bialowieza National Park.


In the article, I used, among other things. From the works:

[1] [9]Assumptions for the Water Shortage Program for 2021-2027 with an Outlook to 2030, 2019. Resolution of the Council of Ministers dated September 10, 2019. On the adoption of the “Assumptions for the Water Shortage Program for 2021-2027 with an Outlook to 2030 https://isap.sejm.gov.pl/isap.nsf/download.xsp/WMP20190000941/O/M20190941.pdf

[2] Kaminski K., 2022. Analysis of surface runoff from the area of Poland including atmospheric precipitation and retention. Master’s Thesis in Environmental Engineering. Department of Hydrology, Meteorology and Water Management, Warsaw University of Life Sciences.

[3] Absalon D., Pieron Ł., Matysik M., Habel M., 2022. Loss of capacity of key dam reservoirs in Poland. Monographs of the Committee on Water Management of the Polish Academy of Sciences 45, 121-134.

[4] https://www.gov.pl/web/retencja/zasoby-wodne-i-retencja (accessed March 12, 2023).

[5] Kaca E., Kaczmarczyk M., 2011. Water reclamation. Status and needs. In: The role and importance of water reclamation in the light of contemporary conditions. State Control. Special Issue 1. Supreme Chamber of Control, Warsaw.

[6] https://www.ckps.lasy.gov.pl/retencja-nizinna-w-lasach#.ZBdkwnbMK5c (accessed March 12, 2023).

[7] [8] Wojda R., Zygmunt G., 2012. The impact of carp ponds on the quality, retention and water balance of the catchment. Fisheries Communications 3, 1-8.

[10] [11]Biedroń I., Brzóska P., Dondajewska-Pielka R., Furdyna A., Gołdyn R., Grygoruk M., Grześkowiak A., Horska-Schwarz S., Jusik Sz., Kłósek K., Krzymiński W., Ligięza J., Łapuszek M., Okrasiński K., Pawlaczyk P., Przesmycki M., Popek Z., Szałkiewicz E., Suska K., Żak J. 2020 National program of surface water restoration. Państwowe Gospodarstwo Wodne Wody Polskie, National Water Management Authority, Warsaw.

[12] Biedroń I., Dubel A., Grygoruk M., Pawlaczyk P., Prus P., Wybraniec K. 2018. A catalog of good practices in hydroelectric works and maintenance works with the establishment of rules for their implementation. https://www.mos.gov.pl/fileadmin/user_upload/mos/fundusze_srodowiskowe/POIiS/Ogloszenia_POIiS/Aktualnosci/KDP_01_-_Katalog_dobrych_praktyk.pdf (retrieved 11/03/2023).

[13] Pusłowska-Tyszewska D., Banaszuk P., Korniluk M., Fabiszewski M., Grygoruk M., 2022. Socioeconomic and natural tasks of the Siemianowka Reservoir – the search for a compromise. Monographs of the Water Management Committee of the Polish Academy of Sciences 45, 109-119.

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