Definition:
Artificial ponds are used to retain rainwater. They keep water all year round, collecting rainwater, or that of the high water in the river. They constitute extensive water and recreation complexes (therefore the areas around the ponds should also be designed). The water in the retention ponds is maintained for 14-21 days at a constant level of up to 2 meters (up to 1.5 m below the bottom of the reservoir, the ground should be above the groundwater table, absorb water at a rate of 12.5 mm/h). The minimum area of a water reservoir should be 5 ha. The retained water is then released in a controlled manner. They are used in large recreational areas or in housing estates. These water bodies should have a varied form and imitate natural water reservoirs. They should also be adapted to the natural landscape
Environmental benefits: mitigation of surface water runoff, retention and infiltration of rainwater, reduction of the risk of flooding, rainwater purification, reduction of the urban heat island, air purification, reduction of water runoff to the sewage system, increase of biodiversity (creation of aquatic ecosystems)
Social benefits: new spaces for recreation, beneficial effects on mental and physical health of local communities, increasing the esthetics of the place, education of local communities.
Economic benefits: increasing the value of the space concerned, increasing the price of housing.
They are part of creating green networks in the city:
– rain gardens, green walls, bioswales, swales, river floodplains.
The solution for professionals.
Construction:
– For the construction of retention reservoirs, we use natural depressions of the terrain, if there are no such depressions in a given area, we dig a small basin or separate a given space for the reservoir by building dikes (we choose such places where water stops during rainfall). If the reservoir is to be used to control river states, it should be located in the middle zone of their catchment area.
– They are designed for rainfall occurring every 100 years. When building, we also take into account data from storm reports (frequency and amount of rainfall), the extent of the catchment area, slope, and drainage.
The structure of the pond consists of several zones:
a) rainwater preliminary treatment zone, before it flows into the pond,
b) shallow water zone: the area where the water is very shallow and is often only temporarily flooded with water, is located around the entire perimeter of the pond, it should be of various widths. It should be planted with coastal zone vegetation (swamp vegetation). We must remember that in this zone the water surface may vary within 25 cm. The transition from the shallow zone to the deep zone should be smooth and gentle so as to create different coastal zones, which will enable the creation of diverse habitats for fauna and flora.
It is also a safety zone for people and animals to avoid falling into the deep zone of the pond. In addition, the creation of shallow zones is conducive to the reproduction of aquatic fauna, it is also a place of exit from / entry into the water for birds, reptiles or amphibians.
The shallow zone area should be along the perimeter of the pond, the depth of the zone from 15 cm to 30 cm, the width of the zone at least 1.5 m (if there are fish in the tank, they should be allowed to hibernate in the pond).
c) main zone, open water – the pond depth should not exceed 3,5m – 4m. Here, sedimentation and nutrient uptake by phytoplankton take place.
Additional components:
– water is supplied to the pond by a system of channels, this length of the flow should be 3 to 5 times longer than the width of the pond itself. Increasing the flow path can be achieved by meandering the channel and creating dams and partitions.
– emergency overflow, it is activated in the event of overfilling the pond volume, improperly designed may result in water overflow and local flooding.
Important: Natural ponds are not used as retention ponds due to contamination from surface runoff retention waters.
– These reservoirs should be regularly cared for, and the accumulated sediment of impurities should be removed from the pond (about 70 – 80% of sediment is retained in the tank).
Building a reservoir step by step:
– Clearing the area, removing the existing vegetation, removing the top layer of soil.
– Shaping of the flood embankment, it should be 10% higher than the designed one, because the soil will still settle on it.
– The pond water inlet should be designed to reduce the speed of the water flow into the retention reservoir.
– In front of the main pond there should be a small water reservoir with the size of 10% of the entire project, where the initial water purification will take place.
– Open water should constitute 50-75% of the total reservoir.
– They require properly prepared drainage, but where large amounts of pollutants are involved, the bottom of the reservoir should be properly secured so as to minimize the possibility of contamination of groundwater.
Vegetation selection:
We use native species, adapted to the respective zones of the pond.
References
http://nwrm.eu/measure/retention-ponds
http://nwrm.eu/sites/default/files/nwrm_ressources/u11_-_retention_ponds.pdf
http://geoservergisweb2.hrwallingford.co.uk/uksd/information/Retention_Ponds.pdf
https://www.researchgate.net/publication/322133196_Making_Retention_Pond_as_an_Attractive_Element_for_Site_Planning_at_Lowland_Housing_Area
https://udfcd.org/wp-content/uploads/2014/07/T-07-Retention-Pond.pdf
Rainwater ponds for buffering and purification of moderately polluted water
https://www3.epa.gov/npdes/pubs/pondmgmtguide.pdf
https://www.davey.com/hoa/elements/pdf/5-3%20retention%20and%20detention%20basins.pdf
https://sswm.info/sites/default/files/reference_attachments/Retention%20Basin.pdf
https://mwik.bydgoszcz.pl/index.php/component/attachments/download/445
Examples:
Retention pond on the Potok Służewiecki brook.
The retention pond is one of the many water reservoirs in the Potok Służewiecki brook (catchment area 34.6 km2). The pond area is 2.4 ha/ capacity 28,000 m3 (maximum 42,000 m3). Depth 1.15 m / max. 1.9 m. There are islands for waterfowl on the reservoir. Reeds grew around the reservoir, which is an important element in the water purification process. The entire complex is surrounded by recreational space used by local residents.
More about the retention reservoir, incl. technical drawings on the website: https://www.iwaw.pl/obiekt.php?p=443200810
Miasteczko Wilanów – a housing estate with many retention reservoirs.
In the area of Miasteczko Wilanów in Warsaw, we have many retention facilities that store rainwater. They are an integral part of individual housing estates, and have a recreational and esthetic value.
A retention reservoir at the facility of Platinium Business Park.
The reservoir retains rainwater, but it is also designed in such a way that it is a recreational space for both residents of Służewiec and people working in the surrounding office buildings.
