Infiltration trenches in Kungsbacka, Sweden | Natural Water Retention Measures

General

National Id

Sweden_02

Site name

Kungsbackaån catchment area, Kungsbacka

Summary

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.

Light or indepth?

Light

NUTS Code

Västsverige

RBD code

SE5

Transboundary

Data provider

Mats Ivarsson, Enveco

Source(s)

Pollutant Removal Efficiencies and Flow Detention of Infiltration Trenches

NWRM(s) implemented in the case study

Infiltration Trenches

Longitude

12.069297

Latitude

57.514515

Site information

Climate zone

cool temperate moist

Mean rainfall

900

Mean rainfall unit

mm/year

Average temperature

Mean runoff

500

Mean runoff unit

450 - 600 mm

Average runoff coefficient

0,560000002384186

Type

Actual Test Site

Monitoring maintenance

Monitoring impacts effects

Performance

Performance impact estimation method

Laboratory

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.

Design & implementations

Application scale

Plot

Lifespan

Age

Performance timescale

Immediate

Area (ha)

1,20000004768372

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.

Constraints

Null

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
Other	Initiation of the measure		The municipality of Kungsbacka

Lessons, risks, implications...

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

Financing type	Comments
Private funds

Barrier

Barrier type	Barrier role	Comments

Driver

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, general governance and design targets

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
Primary	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

Socio-economic

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

19255

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

1925

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

19255

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

Biophysical impacts

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