Dagvatten i Märsta
Stormwater in urban areas has been treated as a problem for a long time. The large proportion of impermeable surfaces inhibits the water from infiltrating in the ground to the same extent that it does in nature. This causes intensive surface flow during rain, which in turn causes inconveniences...
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| Formato: | Otro |
| Lenguaje: | sueco sueco |
| Publicado: |
2008
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| Materias: | |
| Acceso en línea: | https://stud.epsilon.slu.se/12173/ |
| Sumario: | Stormwater in urban areas has been treated as a problem for a long
time. The large proportion of impermeable surfaces inhibits the water
from infiltrating in the ground to the same extent that it does in nature.
This causes intensive surface flow during rain, which in turn causes
inconveniences such as decreased accessability, floods and increased risk
of desease spreading. Drainage through pipes is the traditional and usually
functional metod for storm water disposal. That is as long as water flows
are moderate. But precipitation varies naturally in amount and intensity
and additional impermeable surfaces make some pipes insufficient for
heavy or lasting precipitation. Poor infiltration will in the long run disturb
the balance in groundwater levels. In addition to this there is also a need
for alternative methods that handle the pollution, a need which has been
stressed more and more in the last decades.
Older sewer systems combine storm water with wastewater for treatment
in purification plants. That way pollution is taken care of; but intensive
waterflow decreases the puification effect and pipe overflows can occur in
lowland areas. Since the second half of the 20th century, all new stormwater
systems are separate from wastewater systems. Stormwater is disposed in
nature, which means a risk for species and ecosystems.
Today ponds, wetlands and permeable surfaces are often seen in urban
environment. These are examples of "ecological stormwater handling",
which has had a breakthrough connected to the strife for sustainable
development. The idea of ecological stormwater handling is to lead the
water back into its natural cycle and let natural processes take care of the
purifi cation. Using stormwater in the urban environment also gives other
benefi ts. This type of facilities are often designed as nice recreational
areas and at the same time the visual water cycle can have an educational
function. In some cases it is directly economically beneficial to replace the
traditional systems with ecological ones. It is important that the natural
systems used for stormwater handling are not at risk of being damaged.
Since the 1970's the leading term for alternative methods for stormwater
handling has been "local stormwater treatment". Together with the
development of techniques and the exchange of ideas, a multitude of
expressions have come to be used for description of similar phenomenons.
Here "ecological stormwater handling" is used as the main term since
it is understandable and quite well established. Within this term "local
stormwater treatment" has a more narrow definition.
The purpose of the proposal is to show an example of how the methods
presented can be taken into practical use. Märsta is a small but expanding
town in Sigtuna municipality just north of Stockholm. There are already
a number of stormwater treatment facilities and the opportunities of
craeating a coherent ecological stormwater system in the urban area. The
new facility is to be situated in Steningedalen nature reserve, which streches
from central Märsta toward lake Mälaren. The creek of Rosersbergsbäcken
has its natural outflow into the stream of Märstaån, which runs through
Steningedalen valley. But it is led into a culvert a little further upstream.
The idea is to restore the creek and lead it through sedimentation ponds and
to merge with Märstaån and at the same time improve the accessability to
the area for the inhabitants in Märsta. By linking toghether the new facility
with existing ones, a long continuous green strip is created through Märsta
and all the way down to lake Mälaren. It will also be a link in a blue-green
park strip through Märsta. |
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