Fresh approaches to stormwater management | Uponor

Treating stormwater close to the source

Fresh approaches to stormwater management

The city of Lahti, Finland was planning a new residential area named Ranta-Kartano. A significant challenge the city planners faced was that they needed to reserve a part of the site for the treatment of stormwater before it drained into nearby Lake Vesijärvi. In recent years it has become much more apparent how stormwater carrying nutrients such as phosphorus as well as heavy metals strain the environment, and Lake Vesijärvi was already under significant stress from phosphorus runoff.

Stormwater a major environmental problem
According to Lahti’s Water Protection Planner Juhani Järveläinen, it has been estimated that stormwater is responsible for approximately one third of the phosphorus that ends up in Lake Vesijärvi. Järveläinen points out, “This really is a significant amount. There are over 40 stormwater drains in the city that lead directly to the water system and we clearly had to do something about all this stormwater.”

Testing a hybrid solution
A range of measures had already been taken to address the runoff-caused eutrophication of Lake Vesijärvi. The lake has been re-oxygenated, invasive fish species have been removed from the lake, and protective zones have been implemented next farm fields in the vicinity of ditches and waterways.

Yet Järveläinen says that despite these measures, “We knew we couldn’t reach a sensible end result if we didn’t properly address the external loads as well.” For this reason, the Ranta-Kartano site was one of several selected in which new kinds of solutions for the cleaning and management of stormwater runoff are currently being tested to protect Lake Vesijärvi. Cleaning this runoff by removing phosphorus and heavy metals before it reaches the lake requires a number of mutually supporting strategies – what planners refer to as a “hybrid solution”.

Innovative approaches, clear goals
The concrete objective of the Ranta-Kartano project was to halve the phosphorus load in Lake Vesijärvi. “In a densely built city, each square meter is in demand.” Järveläinen says that the city saw in Ranta-Kartano an opportunity to design the new residential area in a way that enables reserving a part of the site for stormwater treatment.

In fact, the Ranta-Kartano project was deemed promising enough to be selected as a key project in the Finnish government’s national program for the management of stormwater, and for this reason it received a 300,000 euro subsidy from the Ministry of the Environment for its implementation. In exchange for the subsidy, the city will share the experiences it has gained from the project and seek new solutions for the stormwater management together with businesses.

A range of integrated strategies
In Ranta-Kartano, the hybrid solution was to slow down, absorb and filter stormwater before it could reach the lake, through combination of green spaces, green roofs – and Uponor designed and fabricated box-shaped stormwater filters.

Each element plays an important role in the chain, in part because they ensure that not all stormwater ends up being processed at the same time. Construction in Ranta-Kartano started in May 2017, and will continue until 2019, which means that the plans for the whole area are still in their preliminary stage.

Storm water solutions | Uponor
Uponor stormwater management

“Together, these solutions help to filter and store daily rainfall of approximately five millimeters,” Järveläinen says. “If the rain is heavier, the water is routed to a bioretention basin on the northern edge of the area. The system is also equipped with an overflow system for the water that cannot be processed immediately. This overflow water is directed via the emergency drain to Western Hennala, where an extensive processing area for stormwater, consisting of bioretention basins, sedimentation basins and wetlands, is being built. From there, the processed stormwater is sent onward to the Porvoonjoki river.”

Uponor filtration systems put to the test
While the designated green spaces and green roofs effectively slow down stormwater, the Uponor-designed filters do this – and more. These box-shaped filters, with a length of 2.6 meters and a width and depth of 1.2 meters, slow rain water’s journey to the lake while also detaining debris and collecting sand, oil, heavy metals and harmful agricultural nutrients.

Three of filters have been installed on the Ranta-Kartano site, each of which collects stormwater from an area of 150–200 square meters and can store up to 10 millimeters of rain per day. Filters can be installed, for instance, near parking areas, streets, roads and near foot and bicycle paths, as well for the processing of runoff water from roofs.

Fine-tuning over time
According to Niila Tast, a product line manager at Uponor, each filter is equipped with a slightly different filtering material. Researchers at the University of Helsinki will measure the quality of the water and the efficiency of the Uponor filters for a period of two years, and Uponor specialists will also continue monitoring the filters with similar measurements after this period. Tast comments, “In Lahti, our main goal is to remove phosphorus, which is why we wanted to test materials we believe are particularly well suited for this purpose. This is a pilot project, and the idea is to develop the filters into a product for sale.”

Local solutions are often best
One of the advantages of the filters devised by Uponor specialists is that stormwater can be cleaned right away. Tast emphasizes, “Stormwater should be purified as close to its origin as possible. This way, the amount of water remains reasonably small and the impurities are easier to remove.”

It’s important to note as well that the small size of Uponor’s filters enables installation even in densely built urban areas. Lahti’s Water Protection Manager Ismo Malin is convinced that distributed treatment solutions are more sensible than centralized solutions. Malin says, “In the end, distributed stormwater solutions process significantly more water. If the treatment is centralized, stormwater is often directed close to the water system, where the soil is loamy and the natural filtration of water inefficient.”

Stormwater treatment increasingly important
While in the past the approach to stormwater was to divert water into large drainage pipes that often emptied directly into lakes and streams. Increasingly, property owners have direct responsibility for stormwater management in their area. Additionally, stormwater may even be seen as a resource. Minister of the Environment, Energy and Housing Kimmo Tiilikainen says that stormwater management can also be a way of creating a more pleasant urban environment. This is also the objective in Ranta-Kartano, where functional yet also enjoyable green spaces are being increased, and a park-like canal with plants, lawn areas and aquatic plants is being built for directing the water.

Ismo Malin notes that stormwater management also affects groundwater. “If all water is drained via hard surfaces and sewers into the waterways, the amount of groundwater is reduced. Natural stormwater management therefore also improves water resource management on a wider scale.”

Significant benefits well beyond Lahti
Other cities and businesses will also benefit from the Ranta-Kartano project, as Lahti will publish reports on the key project. The government has been pleased with the progress of the project. Minister Tiilikainen is particularly pleased about the way in which the project combines city planning with water protection, commenting, “The comprehensive stormwater management system planned in Lahti is a prime example of a multi-disciplinary and forward-looking local cooperation project, in which businesses also develop innovative and practical solutions.”