The article is from A&B issue 10|23
Currently, only 6.5 percent of rainwater in Poland is subject to retention, and experts say it is possible to raise this figure to 45 percent. On average, the country retains 1,800 m³ of water per capita per year, which is very poor compared to the European average of 5,000 m³. Only Malta, Cyprus and the Czech Republic are worse. The forecasts are unforgiving and bring us closer to "water stress," or the threat of a water deficit, the threshold of which has been set at 1,700 m³ per person. Climate change and recurrent drought mean that in some regions annual precipitation does not exceed 400 mm.
Open stormwater drainage systems can be the basis for reducing retention charges
Photo: © James Frewin unsplash.com/photos
On average, Poland's water resources amount to 60 billion cubic meters, which ranks us third from last among European countries. During periods without rain, and these occur more and more often, this average drops by 1/3! In addition, global water consumption is increasing every year, by an average of 1 percent. According to UN data, the rate of water consumption has increased as much as six times over the past century.
Water from precipitation can be retained in various ways: in natural depressions (trough retention); in the topsoil (surface retention); on plants (interception); in lakes, rivers, ponds and artificial reservoirs (reservoir retention); in river basins (trough retention); in swamps, marshes, bogs, moors (standing water retention).
Retention reservoirs retain only 6 percent of rainwater, which is why we so badly need small retention systems that will naturally and non-invasively improve the water balance of a region on a micro scale. The huge water retention problem of Polish cities is a consequence of inadequate spatial policies, including draining swamps, regulating rivers and channeling small watercourses in concrete channels. Prolonged periods of drought are interspersed with episodes of short, but extremely intense, torrential storms. The pattern of precipitation has changed: up to 3/4 of the monthly average rainfall can fall in an hour. As, for example, in Krakow's Biezanow district, where in August 2021 water flooded many residential structures, reaching a meter high and even more. The problem is an outdated rainwater sewer system designed decades ago and ill-suited to accommodate such a large amount of rainfall in a short period of time.
The idea of a sponge city rather than further concretization is the direction of the future
photo: © Yanalya pl.freepik.com
The Institute for Environmental Protection estimated that between 2001 and 2016, Poland suffered losses of 78 billion zlotys in damages to infrastructure and property as a result of drought and storm surges. In addition, every five years we bear the huge financial consequences of these phenomena, exceeding 1 percent of GDP.
Urban retention should be approached comprehensively and take into account urban infrastructure, private property and developer investments. Modern technologies make it increasingly possible to realize the idea of a sponge city. These include, for example, water-permeable sidewalks, bike paths and roads, green roofs or reservoirs that store and filter water. As far as Polish cities are concerned, a good model is Gdansk, where more than a dozen rain gardens have already been established to capture up to 40 percent more rainwater than traditional lawns. The plantings use hydrophytic vegetation, which means they tolerate a high proportion of water in the ground. In addition to their retention function, they also have a phytoremediation function, that is, they clean rainwater and soil of heavy metals. As part of the Gdansk Small Retention Policy, rain gardens are being built with the participation of developers, and any city resident can apply for a subsidy for such an investment in their garden.
Regulating rivers leads to huge water deficit in cities
photo: © Kai Pilger unsplash.com/photos
Improving retention in cities also means establishing green roofs to capture 30 to 100 percent of rainwater. In metropolitan areas, most such developments are being built on the roofs of parking lots and garages, and the most famous green roof is the one belonging to the Warsaw University Library (Irena Bajerska was the designer of the garden).
Water-saving solutions are increasingly being implemented, and they don't have to be complicated at all. Water-saving fixtures - showers, washbasins, sinks - have been used in the Gate of the City in Łódź (designed by Medusa Group). The innovations introduced there have an extremely positive effect on the project's energy balance, and water consumption has been reduced by half. The water supply is controlled by motion sensors, while the systems automatically cut off the water supply in times of failure.
Developers have also begun to practice water retention. In the Generation Park office complex in Warsaw (designed by JEMS Architekci), Skanska has opted to collect water in a tank under the building, from where it does not immediately go into the sewage system, but is used for sanitary purposes. This maximizes the use of available water resources. The same company used outdoor solutions in the Wave office complex in Gdansk (designed by Medusa Group) to reduce rapid surface runoff after heavy storms. There is a green area in the immediate vicinity to relieve pressure on the local rainwater drainage system, and there are plans to create a recreational area with a retention tank underneath to provide protection against flooding, the water collected there will be used to irrigate the garden in times of drought.
Without urban retention, it will be increasingly difficult for us to respond to dynamic climate change
photo: © vecstock pl.freepik.com
The capital has developed a program called "Climate Change Adaptation Strategy for the City of Warsaw until 2030 with an Outlook to 2050." Its scope included recommendations that talk about reducing impervious surfaces, restoring and building retention areas, revitalizing water bodies, protecting and properly caring for existing and planned green areas, including new squares and pocket parks. The Greenery Board is establishing flower meadows, and has reduced the amount of mowing of green areas and along streets in a total area of 220 hectares. In addition, it is making two water intakes from the Sluzewiec Creek to feed the dry ponds in the Sluzewiec Valley. This will make it possible in the future to take over some of the creek's water appearing after a downpour, lowering the risk of flooding in nearby areas.
Another project that plans to increase retention in the city is the "Warsaw rushes," which is being implemented by ZZW starting in 2020. It concerns the adaptation of the damming structure on the Sobieski Canal for the Morysin Nature Reserve and the construction of drainage levees in the Kabacki Forest Nature Reserve. Warsaw also plans to build more collectors to increase retention: Wislane, Linde-Bis and Mokotowski-Bis. All investments are scheduled to be completed in 2023.
In 2019, the investment "Management of rainwater in the city of Gorzow Wlkp." was launched. The city received nearly PLN 70 million in funding for its implementation. It is carried out in the area of four catchments of the Warta River, and includes the construction and modernization of 14 km of rainwater sewers, 26 new retention tanks throughout the city and the renovation of existing ones with an area of 25,500 m3. The plans include the creation of accompanying infrastructure: community water points, toilets, a walking path and playing fields. This is one of the largest retention programs being implemented in Polish cities. It is expected to end in 2023.
During heat waves, water levels in rivers can drop more than twice
photo: © vecstock pl.freepik.com
In the Water City Index 2020 report, among Polish metropolises, Bydgoszcz ranked high - it came in second place. A total of 218 cities were evaluated, which consistently and effectively implement policies to increase retention in their areas. Several years ago, Bydgoszcz Waterworks was the first in Poland to put water and sewage management in a comprehensive order. Now the city is changing its philosophy of rainwater management, implementing the concept of distributed retention. Water from several reservoirs will be used, among other things, to water the city's greenery, fill ponds, and only the unused surplus will be discharged into the river. The mayors are implementing the idea of a sponge city. In the competition of the National Environmental Protection and Water Management Fund, the concept of adaptation of Bydgoszcz to climate change was recognized as the only one in the country that solves the problems of functioning and management of rainwater on a city-wide scale. The project is distinguished by its innovativeness and comprehensiveness, thanks to which it received significant support from EU funds: the total value of the project is 258 million net, while the amount of the grant is 154.8 million net. There will be 14 km of new rainwater channels, 71 retention tanks, 3 infiltration box tanks, 22 rainwater treatment plants and 11 outlets to receivers. Renovation of existing rainwater channels with a total length of 90 km by trenchless methods is also to be carried out.
Wody Polskie reports that the level of retention in Poland is 6-7 percent, while the European average is 15-20 percent. It is known that in cities this value is even lower. To meet the challenges of climate change, including in economic terms, this percentage should at least double. A broad spectrum of legal and financial tools is needed for both developers and residents to consider sensible and effective measures to increase urban retention.
Krzysztof Mielicki
photo: author's archive
Krzysztof Mielicki - landscape architect, owner of the ZIELONE POJECIE studio. He gained practice working in Barcelona and Paris. His design idea is to strive to find a balance between the development of civilization and connection with nature.
