Tree pits
The structure is in the form of a pit immersed in the ground, in which, additionally, a tree grows. They are used for rainwater retention. Water enters the pit thanks to the holes in the curb. The water then flows through the gravel filter and the excess water is discharged into the soil, some of the water is absorbed by the trees and evaporated by the leaves during the evaporation process. The solution is installed near the road lane (between the street and the sidewalk). The pit can be used for one tree or a group of trees. In addition to the rainwater retention, it is also purified. Tree pits should be used in spaces where salt is not used in winter for de-icing the road.
Environmental benefits: rainwater retention, reduction of surface runoff from paved areas: sidewalks, parking lots, streets, rainwater purification (sedimentation of pollutants, phytoremediation), increasing shading in the city, reducing air temperature, increasing biodiversity and creating new habitats for fauna in the city.
Social benefits: decorative aspects.
Economic benefits: Reduction of the costs of rainwater discharge into the storm sewage system (they also reduce the risk of overloading it).
They are part of creating green networks in the city: together with green roofs, green walls, rain gardens, bioswales.
The solution for professionals.
Construction:
– The facility should be designed to store the so-called storm peak (preventing the backflow of water from the pit).
– They are made in areas with a slope of not more than 5%.
– In the excavation made, we place a system of underground supports that are foundations for the tree protection grate (it is important to adjust the size of the grate opening to the given tree species) and the surfaces around the tree. It is important that the native soil is not compacted around the tree (which is crucial for free infiltration of rainwater). The supports are made of plastic and have the form of a pit with the dimensions of 400 mm of height / 600 mm of width / 1200 mm of length.
– Both native soil and a specially composed mixture facilitating infiltration are used here. It is also possible to apply underground drainage connected to the rainwater drainage system.
Greening
– In pots, tree roots have a chance to proliferate freely, many plant species can be used here, preferably those characterized by strong water transpiration.
– When creating a project, particular attention should be paid to the underground infrastructure existing in a given place.
Examples:
More about rainwater retention by means of these systems at: https://greenblue.com/
https://cms.esi.info/Media/documents/77739_1534320723395.pdf
https://www.denvergov.org/files/assets/public/doti/documents/standards/pwes-013.0-ultra_urban_green_infrastructure_guide.pdf
https://mwik.bydgoszcz.pl/index.php/component/attachments/download/445