Infiltration trenches in Kungsbacka, Sweden

National Id
Site name
Kungsbackaån catchment area, Kungsbacka
The study is carried out by flow weighted sampling at the inlet and outlet of one infiltration trench in Kungsbacka south of Gothenburg, located under the parking lot of a supermarket. The observations and sampling were conducted during April to June 2012 and the results from five storm events were analyzed.
RBD code
Data provider
Mats Ivarsson, Enveco
NWRM(s) implemented in the case study
Climate zone
cool temperate moist
Mean rainfall
Mean rainfall unit
Average temperature
Mean runoff
Mean runoff unit
450 - 600 mm
Average runoff coefficient
Actual Test Site
Light or indepth?
Monitoring impacts effects
Performance impact estimation method
Performance impact estimation information
The experimental procedure consisted of stormwater sampling at the infiltration trench in Kungsbacka. Five storm events from April to June, in 2012, have been analysed. After sampling, water quality analyses have been performed; such as heavy metals, total suspended solids (TSS), volatile solids (VS), total inorganic nitrogen (TIN) and phosphate-phosphorous (PO4 3-). The pollutant removal efficiencies have been determined using a mass balance approach, based on flow-weighted samples collected from the inlet and the outlet of the infiltration trench. Moreover, Event Mean Concentrations (EMC) have been calculated for each storm event. The flow detention of the infiltration trench has been measured by flow meter devices installed at the inlet and outlet of the infiltration trench and the results are presented as
hydrographs. Based on the observed detention characteristics, the flow detention function has been evaluated and compared to the design capacity.
Application scale
Performance timescale
Area (ha)
Design capacity description
Maximum volume of stormflow that can be retained is 243 m3. Studies from the Swedish road administration and others show show that reduction (%) of pollutants in infitration trenches varies according to: TSS 50-90, TP 10-50, TN 55-84, Zn 15-90, Cu 10-90, Pb 30-80, Cd 10-50, Oil and Greas 100, BOD COD DOC 89-93, Bacteria 90, NOx 82.
Favourable preconditions
The measures was constructed as part of the development of the industrial and commersial area.
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Design consultation activity
Activity stage Key issues Name Comments
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
Initiation of the measure
The municipality of Kungsbacka
Key lessons
The pollutants; suspended solids, heavy metals, nitrogen and phosphorus were analyzed. The results show that the pollutant concentrations of the inlet are in accordance with typical stormwater pollutant concentrations in Gothenburg and the outlet mean concentrations are below the compared discharge guideline values. The results also show that the infiltration trench has an average removal efficiency of 80% for suspended solids, approximately 50% for total inorganic nitrogen and all removal efficiencies for heavy metals wereover 50%. Zinc, lead, copper and chromium have removal efficiencies of 70-80% while cadmium and nickel have removal efficiencies of 50-60%. The observed flowhydraulics showed good flow detention since the outflow hydrographs were generally significantly lower than the inflow hydrographs for all storm events.
Success factor(s)
Success factor type Success factor role Comments
Existing technical standards
main factor
Financing type Comments
Private funds
Barrier type Barrier role Comments
Driver type Driver role Comments
Legal obligations
main driver
In Sweden, the responsibility for adressing the issue of storm water is delegated to the municipalities. The actions are regulated in a number of policy frameworks; the Swedish environemntal code, containing the national implementation of WFD plus a number of other national regulations, the Plan and buildning act regulating the planning process which also covers stormwater issues, the Swedish Road act and the Water services act.
Financing share
Financing share type Share Comments
Policy description
The main function of infiltration trenches is to control the stormwater flow and to reduce the pollutant load of the stormwater. The measure targets the WFD pressure 2.1 Diffuse - Urban run-off by reducing the discharge of nutrients and hazardous substances carried by stormwater.
Part of wider plan
Policy target
Target purpose
Pollutants Removal
Peak-flow reduction
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Water Policy - WFD
Stormwater, policy and guidelines
Policy impact
Impact directive Relevant impact
Policy wider plan
Wider plan type Wider plan focus Name Comments
Policy requirement directive
Requirement directive Specification
Direct benefits information
There are no monetary valuation of the direct benefits accruing from the infiltration trench available. Qualitatively, the direct benefits can be described as reduced risk for flooding of the parking lot in connection to the supermarket, and adjacent areas, during events of extreme precipitation.
Ancillary benefits information
The aditional benefits from this measure are connected to reduced eutrophication in the Kungsbackaån and in the coastal water receiving the river discharge, strengthened biodiversity in both the Kungsbackaån and in the coastal water due to reduced discharce of pollutants and harmful substances. Positive effects can also be anticipated on cultural ecosystem services such as recreation in the affected areas.
Costs investment
Costs investment information
The figure is an estimate based on the proxy 700 SEK/m3 (79,2 €/m3) from the Swedish consultancy firm Norconsult (À-Prislista Markarbeten, Gothenburg 2010-06-01: Norconsult 2010)
Costs operation maintenance
Costs operation maintenance
The general estimation is that the maintenance costs are
ranging between 5 and 20 percent of the construction costs. The value in the field represents 10% of the construction cost.
Costs total
Costs total information
Maintenance costs are not included.
Ecosystem improved biodiversity
Information on Ecosystem improved biodiversity
Reduction of nutrients and hazardous substances will improve the overall ecological status in Kungsbackaån and the coastal water receiving the river discharge.
Ecosystem provisioning services
Ecosystem impact climate regulation
Not relevant for the specific application
Information on retained water
The infitration trench and associated retention pond can therorethically contain 243 m3.
Information on increased water storage
The therorethical maximum volume stored per area equates to 202,5 m3/ha.
Information on runoff reduction
The maximal allowed discharge of stormwater from the parking lot and area for loading to
the stormwater ponds is 15 l/s of detained flow
Water quality overall improvements
Positive impact-WQ improvement
Information on Water quality overall improvements
Reduction in discharge of nutrients and hazardous substances
Soil quality overall soil improvements
N/A info


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