Urban areas
Rain Gardens as a Way of Adapting Cities to Climate Change Foto: Gdańskie Wody

Rain Gardens as a Way of Adapting Cities to Climate Change

Jury Award in the Adapterra Awards 2019

Small retention facilities are an important element of the rainwater management in Gdańsk. They mimic nature in collecting, purifying and delaying rainwater runoff. Number of urban rain gardens and mini retention parks now slowly increases, but big part of the project is to encourage, educate and support the residents even further, so that they can build such solutions on their own.

Guide for Small Retention that is being created should also help to reach this goal as it shows how to design, build and use such solutions in the urban fabric. It is a great tool not only for city inhabitants but also developers.

The Adaptation Journey

 
The positive impact
Forecasts for climate change for Gdańsk indicate that in the perspective of 2050 the tendency for rapid floods and prolonged droughts will deepen.

The project allows for better environmental management and raising awareness about the need to retain and reuse rainwater as a valuable resource rather than waste. The project presents ecological solutions covering various types of natural retention reservoirs. Vegetation of these rain gardens prevent or reduce the effects of floods and urban areas caused by heavy rains and other phenomena related to climate change.

Green infrastructure will relieve sewerage, maintain greenery during hot season and improve microclimate in the city. This solution also reduces the problem at the source by slowing rainwater outflow and recreating degraded ponds. This will also help to feed the groundwater instead of quick evaporation or down flow on otherwise sealed surfaces.

What's more, the proposed activities will help to ensure the quality of water discharged to the receiver.
 
How does it work?
Rain gardens collect rainwater from the so-called sealed areas. If it is a roof, the garden is fed with gutter water. In the case of water from sidewalks or roads, it is necessary to make appropriate slopes or cut curbs to allow water to flow into the recess of the garden. Excess water accumulated in the basin goes to the traditional rainwater drainage system.

Thanks to the appropriate vegetation and soil-filtering layers, the rain garden is able to pre-clean the water and introduce it into the deeper layers of soil. If the ground conditions are not conducive to water absorption, a garden in a container or in a sealed ground can be arranged – due to evaporation of water, its final volume decreases, and the drainage into the sewage system is delayed in time.

The solution includes adding 500 cubic metres to retention capacity, increases security for around 1,000 people, creates self-sufficient green area of over 3,500 square metres and give opportunity to almost 100 development projects.

The economic benefits are in reduction of fees for water services, reduction of the amount of runoff rainwater, and thus the risk of flood. It improves the aesthetics of the environment, comfort of life and health of people and increases biodiversity.
 
Original state
The complex conditions of Gdańsk include numerous areas with impermeable clay deposits with intense rainwater runoff and dangerous landslides. Intense housing development further contributes to sealing the surface on one side of the city. On the other side, there is easily permeable surface, which insufficiently protects the underground water against pollution and impact of urbanization.

What is more, the flood threat can exist in a form of rainfall, thaw and storms, as well as ice jams. Another problem is the fact that these types of floods can build-up simultaneously in one area. This fact is a major challenge requiring a variety of activities, including the ecological management of rainwater. Knowledge about environmentally friendly methods of rainwater management is not adequately used in architecture, landscape architecture, urban planning, and spatial planning in Poland.
 
Operation and maintenance
Maintenance: 20,000 PLN annually.

It is needed to work closely with residents who choose places for potential rain gardens. Then, the costs and retention capacity need to be in balance. The field capacity is an estimate and has to be verified during earthworks and the actual capacity is determined after its establishment, on the basis of a measurement carried out with a special device, which is also used to determine the effectiveness of the rainwater drainage network at acceptance.
 
Why was the measure chosen?
The construction of a traditional storm water drainage system requires a lot of time and money. Preparation of a green drainage investment on the other hand, such as a garden, is much cheaper and faster, taking up from one month to a year. Rain gardens are self-sufficient with no additional irrigation except for periods of drought.

This solution with greenery not only improves the environment but also provides greater biodiversity, higher quality of drained water and improves appearance of the landscape.
 
Obstacles and challenges
Tree roots collisions.
 
How much did it cost?
Overall costs are 450,000 PLN and return of investments is 6.66 years. Life expectancy of the investment is 7 years and savings are 550,000 PLN.

Urban greenery Flood control measures Biodiversity Floods and torrential rainfall Lack of water and drought 

Locality:
Gdańsk, Poland
Timeframe:
2018-to date
Author:
Retention team in the company Gdańskie Wody / Legal representative Ryszard Gajewski
Contractor:
Municipality of the City of Gdańsk
Investor:
Company Gdańskie Wody
Contact:
Agnieszka Kowalkiewicz
a.kowalkiewiczhaha.@gdmel.pl

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