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Alma Raingarden; a promising tool for stormwater management

The prefabricated raingarden from Skjæveland is space-saving, easy to install, provides safer winter operation, and can be designed with capacity adapted to each individual project.

Raingardens, submerged terrain planted with natural and site-adapted vegetation, are areas where rainwater is collected and detained. This is achieved by imitating the natural hydrological cycle. Where conditions permit, the water can be infiltrated to the ground. In raingardens, polluted rainwater can also be treated through physical, chemical, and biological processes in the ground.

Precipitation will accumulate in all depressions in the terrain, but in order to be sure that the detention, infiltration, and possibly cleaning takes place in the best possible way, solutions must be properly designed. Therefore, as a collaborative effort between Storm Aqua and Skjæveland Cementstøperi, considerable resources have been devoted to the research and product development of pre-fabricated raingardens.

Results are promising. Pre-fabricated raingardens have been delivered to projects locally and in the eastern part of Norway. Preparations for further market development are ongoing.

The ilustration above: Storm Aqua and Skjæveland has recently prepared a tailormade system for installation at Helsfyr station in Oslo. It is an existing local train station that is being rebuilt. Limited space made it necessary to exploit all available possibilities to detain storm water.

This Alma Rainbed is composed to cover the needs at Helsfyr station.

Must hold and release the water

One of the solutions for Helsfyr station was to assemble three Alma raingardens (series 200) and combine them into a larger unit.

Due to the limited space available, the height of the raingardens is reduced from 1500 mm to 1000 mm. Storm water from part of the surfaces around the station is led into the raingardens and handled in the growth medium.

Excess water is collected in the detention chambers at the bottom of the raingardens. Cartridges have been mounted to pull-up water to the growth medium during dry periods.

Alma raingardens are supplied in three different sizes, which can all be adapted for detention or infiltration. Solutions can be adapted to local situation. Storm Aqua can help to carry out design and capacity calculations. The result of these surveys defines how many beds are needed, and the sizes of these, for the individual projects.

The growth medium in the Alma raingardens is designed to obtain a good balance between infiltrating the storm water and retaining the water to ensure good plant growth.

The growth medium must hold the surface water long enough to provide a detention effect. At the same time, the growth medium must let the water through, so that the raingarden has sufficient capacity to handle the next rainfall. Therefore, it is crucial to be able to control the permeability of the growth medium.

Safer winter operation

The prefabricated raingardens are space-saving and provide good control of the actual operation compared to site-built alternatives.

Storm water is guided into the raingarden where it is detained in the growth medium before it is released into the built-in detention chamber.

The Alma raingardens are provided with an open or a closed bottom, depending on the local ground conditions and the selected drainage mechanism. It has proven effective to combine the raingarden with an underlying subbase, where precipitation is gradually infiltrated to the ground. It can also be combined with a separate concrete basing on the side to increase the detention capacity.

During frost periods, the growth medium will freeze. When rain falls on the frozen growth medium it cannot infiltrate. Therefore, an overflow pipe has been integrated in the Alma raingarden. The overflow pipe guides the water down to the built-in detention chamber, and the raingarden will therefore retain its function also in periods with frost.

Documented effect of growth medium

The design of Alma is based on a combination of Storm Aqua’s expertise in storm water management and research, and Skjæveland’s many years of expertise in product development.

Mette Haugen while working on her bachelor thesis.

In December 2017, Mette Haugen submitted her bachelor thesis titled “Functional description and testing of prefabricated rainbed as a hybrid nature-based LOD measure.”

The thesis was part of the work to document the hydraulic function and to find an optimum growth medium for the raingarden. In collaboration with Storm Aqua and Skjæveland, Haugen tested various alternatives and succeeded in finding a combination that both keeps on and releases the water.

Research-based calculation model

Dennis Kliewer was a master’s student at Fachhochschule Munster, University of applied sciences. In December 2018 he delivered his master’s thesis titled “Runoff Modeling and thereon based Dimensioning of Stormwater Management Solutions: Raingarden and Detention Roof at Considering Norwegian Stormwater Management Practices”.

Dennis Kliewer became familiar with Storm Aqua through the research programme Klima 2050. Through his work, he calibrated Mette Haugen’s findings, calculated the run-off and documented the effect of the rain garden. He developed a calculation program, which Storm Aqua will use in the design of future installations.

Dennis Kliewer while working on his master thesis related to Alma rainbed. To the right Per Møller-Pedersen, general manager of Storm Aqua, who supervised him along the way.

– The observations have made it possible to establish a quality-assured model, explains Dennis Kliewer.
– I observed the infiltration process in the growth medium through several different scenarios and got ample information that I used to establish, calibrate and validate the calculation program.

– Did you get any surprise along the way?

– No I did not. And that is a good thing, because it confirms that the system works the way we had planned before, and that the preliminary analyses also were correct.

Dennis Kliewer fikk god veiledning av Per Møller-Pedersen under forskningsarbeidet.

– How would you describe the contributions of Per Møller-Pedersen and Skjæveland, and how did the contributions affect your work and the process?

– The contributions from Per Møller-Pedersen and Skjæveland were absolutely ideal. I got all the information I needed to complete my master’s thesis, and Per Møller-Pedersen was an excellent supervisor. He assisted through good conversations and meetings, while motivating me to work independently in the process of solving the problems that arose, Dennis Kliewer describes.

Although the function of Alma raingarden is well documented, the Skjæveland Grupp continues its research.

At the moment a raingarden is installed on the group’s test and demonstration field. The goal is to investigate the combination of a prefabricated Alma raingarden and a site-built raingarden. This installation will also be linked to a master’s degree project, being carried out by Anwei Sun at the Water and Environment line at NTNU.

The purpose of the Skjæveland Group is to be a valuable resource and contributor in the work of solving the current and future challenges and tasks. Therefore, the three companies in the Skjæveland Group invest considerable resources in product development, research and quality enhancement.