River Tolka constructed wetland and enhancements, Ireland

General

National Id:

Ireland_001

Site name:

River Tolka

Summary:

The River Tolka runs through Dublin, Ireland. A series of measures was applied to the urban sections of the river to slow flood flows, reduce pollution and support wildlife. These included the establishment of retention ponds to manage runoff storage; bank engineering to slow flows and prevent erosion; and planting trees along the river to slow runoff. Two phases of retention pond construction have been carried out, the latter as part of a wider ‘Greenway’ project to develop a green corridor with cycling route.

The in-depth description of the case study:

cs-ire-01-final_version.pdf

Location description:

The River Tolka is located in eastern Ireland. It flows eastwards through Dublin and in to the Irish sea. The improvement sites are located along the urban reaches of the Tolka, particularly at the Tolka Valley Park.

NUTS Code:

Southern and Eastern

RBD code:

IEEA

Transboundary:

0

Data provider:

Heather Williams, AMEC

Source(s):

The Tolka catchment - fulfilling multiple roles: local government perspectives

Tolka Valley Greenway opening speech by Lord Mayor

Performance Assessment of an Integrated Constructed Wetland-Pond System in Dublin, Ireland

The Tolka catchment - fulfilling multiple roles: local government perspectives

Biodiversity Survey of the Integrated Constructed Wetland at Tolka Valley Park, Finglas, Co. Dublin

Impact Assessment Of Urbanisation On Hydrology For The River Tolka In Dublin, Ireland: A Case Study Of Remote Sensing Supported Hydrological Modelling

NWRM(s) implemented in the case study:

Wetland restoration and management

Urban forest parks

Natural bank stabilisation

Basins and ponds

Longitude:

-6.303277

Latitude:

53.377121

Site information

Climate zone:

cool temperate moist

Mean rainfall:

715

Mean rainfall unit:

mm/year

Average temperature:

11

Mean runoff:

357

Mean runoff unit:

450 - 600 mm

Average runoff coefficient:

0,5

Type:

Case Study Info

Light or indepth?:

In-depth

Monitoring maintenance

Monitoring impacts effects:

1

Monitoring parameters:

There has been varied monitoring at the Tolka. Monitoring relevant to the NWRMs include ecology surveys (incl. macrophytes, amphibians, invertebrates), and water quality monitoring.

Performance

Performance impact estimation method:

Catchment outlet

Performance impact estimation information:

Performance of the retention ponds/ wetlands is monitored by measurements of water quality and observation of fauna and flora

Biophysical impacts

Water quality overall improvements:

Positive impact-WQ improvement

Information on Water quality overall improvements:

The wetland influences water quality on its own. In addition, barley straw bales were added to ponds in 2012 to prevent algal blooms (and can be assumed to have been successful, since there has been no evidence of the algae since).

Wq Improvements n unit:

% reduction pf pollutant

Information on Water quality Improvements (N):

The constructed integrated wetland achieved: - 91% reduction in ammonia concentrations - 16% reduction in nitrate concentrations - 6.5% reduction in nitrite concentrations. The addition of barley straw provided further benefits, reducing ammonia by 55% and nitrate by 38%

Information on Water quality Improvements (e.coli):

The addition of barley straw to the pond/weltand achieved a 99% reduction in e-coli concentrations

Soil quality overall soil improvements:

N/A info

Information on Soil quality overall soil improvements:

Some erosion control measures were implemented on the floodplain of the River Tolka. These measures may improve soil quality by retaining soils, but no specific information was available.

Lessons, risks, implications...

Key lessons:

- Parks in urban areas can serve as biodiversity reserves and offer opportunities to contribute to achieving good ecological status of waterbodies under the WFD. - Soft engineering techniques can be cost-effective and enhance the biodiversity potential of urban cactchments. - Local community involvement is key to project success.

Success factor(s):

Type	Role	Comments
Attitude of relevant stakeholders	main factor
Attitude of the public	secondary factor

Financing:

Barrier:

Driver:

Type	Role	Comments
Balancing different objectives	main driver	There were multiple objectives to the improvements to the Tolka, relating to the WFD, Floods Directive, EU LIFE Project, "Greenway" development, recreational and access objectives in Dublin

Socio-economic

Costs total:

4100000

Costs total information:

Full cost of the 'Greenway' programme of which the ponds and wetlands were part

Compensations annual information:

Assume none (land was already public parkland prior to implementation)

Information on Economic costs - income loss:

Assume none (land was already public parkland prior to implementation)

Ecosystem improved biodiversity:

1

Information on Ecosystem improved biodiversity:

The ecology of the river has improved as a result of these measures and other improvements in the catchment. Otter and salmon have now returned to the Tolka catchment (altough NWRMs are only some of the actions that have contributed to this).

Ecosystem provisioning services:

1

Information on Ecosystem provisioning services:

Angling quality has improved as a result of these and other actions in the Tolka catchment.

Ecosystem impact climate regulation:

No specific impact

Ecosystem erosion control:

1

Information on Ecosystem erosion control impact:

Before and after photos of sediment capture measures reveal less exposed soil on river banks.

Policy, general governance and design targets

Policy description:

The Tolka has poor ecological status (WFD) due to diffuse pollution (urban runoff) and point pollution (waste disposal sites)

Part of wider plan:

1

Policy pressure:

Policy requirement directive:

Policy impact:

Policy wider plan:

Wider plan type	Wider plan focus	Name	Comments
National	Environment & Biodiversity	Renew4GPP (Ireland pilot project)	Control of invasive species

Policy area:

Policy target:

Target purpose
Pollutants Removal
Peak-flow reduction
Improved Biodiversity
Oher Societal Benefits

Design & implementations

Application scale:

River

Installation date:

2000

Performance timescale:

< 1 year

Area (ha):

18.2 ha

Area specifications:

The total size of the Tolka Valley Park is 18.2 ha.

Constraints:

Constructed wetlands depend on suitable hydrological regime that allows permanent presence of water in them.

Favourable preconditions:

Availability of parkland space prior to the project

Design contractual arrangement:

Design consultation activity:

Design land use change:

Design authority:

Authority type	Role	Name	Comments
Other	Initiation of the measure	Dublin City Council	City Council
Other	Financing	National Transport Authority	Funded Greenway
NGO	Other	Tolka Trout Anglers	Volunteer work
	Other	Atkins Global	Consultants

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Last updated: 18 Jun 2015 | Top

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River Tolka constructed wetland and enhancements, Ireland

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