78
O
bjectives
The design and implementation of Nummela GatewayWetland Park aimed to achieve multiple purposes, both biophysical and
social. It was constructed both as a landscape to provide mitigation to the water environment and as an urban park. The
wetland was expected to have a moderate function in treating inflowing water quality before entering the receiving lake,
thus
removingpollutants
(the wetland mean inundated area is only 0.1% of its watershed area, whereas it is commonly
suggested that water pollution control requires 1-5 % wetland area of the contributing watershed area, hence the expec-
tation of only moderate removal rates). The wetland also mitigates peak flows, reducing erosion typically associated with
urbanisation. Furthermore, the GatewayWetland Park targets biodiversity improvement through providing an
oasis for local
fauna
: the park is a gateway for the lake fauna to the stream Kilsoi. Clay-dominated stream habitat is critically endangered
in Southern Finland, so establishment of wide areas of this habitat type within the revived urban and clay-dominated Kilsoi
Stream corridor was attempted. In addition to these biophysical aims, the desire was for the park to provide an oasis for
local people and opportunities for environmental education.
T
hemeasures
implemented
Nummela Gateway Wetland Park was constructed in 2010, on an abandoned crop field where the stream existed as a
straightened and cleared ditch. In winter 2010, land formation works were carried out as winter-time dry excavation, to
provide the basic structure of the site that defined long-term vegetation and habitat establishment. Vegetation was then
allowed to self-establish on the area.
Threehabitat islands
were constructed, the banks of which were secured with bundles
of local willow branches. Native trees were planted during a volunteer event for local residents in order to provide shaded
areas. Typical of an urbanised area, inflow to the wetland fluctuates greatly - from circa 10l/s during dry periods to circa
1 000l/s during heavy rain and snowmelt events. In addition to vegetation, widening of the stream and installation of
stilling ponds and rock structures were used to dissipate erosive flow energies. All old drainage ditches within the site were
blocked to create amphibian habitats that are safe from predatory fish that enter the wetland main pool (many fish spawn
in the spring, from the lake). A bird observation tower was built at the wetland, which offers observation of birds both at
the wetland and in Lake Enäjärvi.
A volunteer event for residents was carried out to plant native shade trees and
install willow bundles to stabilise island banks.
© O.Wahlroos, University
Helsinki (Dpt. Forest Sciences)
