❓ This parliamentary question scrutinises the efficacy of drainage and water management strategies, particularly infiltration policies and Water Sensitive Design, within the Swan Urban Growth Corridor (SUGC), raising concerns about the impact of extensive tree removal and the lack of post-development monitoring and plan reviews in areas with high groundwater.
AnsweredQoN 1631Legislative Council
QuestionView source ↗
(1) What reviews have been
undertaken to determine the efficacy of drainage and water management
strategies within the Swan Urban Growth Corridor (SUGC)?(2) What
studies have been undertaken to determine the efficacy of the infiltration
policy that underpins all drainage strategies within the Metro area with
particular reference to areas of high groundwater?(3) Estimates
indicate somewhere around 100,000 trees have been removed to date with another
60,000 when development is completed within the SUGC south of Gnangara Road.
What studies have been undertaken to determine the impact of the removal of
thousands of mature trees within the district where high groundwater is
prevalent?(4) What
studies have been undertaken to determine the efficacy of Water Sensitive
Design, (formerly Water Sensitive Urban Design), technologies within areas of
high groundwater?(5) Foundation
documents such as the Swan Urban Growth Corridor Drainage and Water Management
Plan 2009 (SUGCD&WMP 2009) that provide the blueprint for Drainage
Strategies and Plans within the SUGC contain a number of measures to establish
the effectiveness of Local Water Management Strategies. These include
post-development monitoring as noted in SUGCD&WMP 2009 - 9.3 Monitoring strategy - Table 9-2 Assessment requirements of
development proposals – monitoring, for a period of three years. Has monitoring inline with these requirements
occurred for development or stages of development within the SUGC and where are
the results?(6) Many
adverse impacts related to drainage strategies in areas of high groundwater,
such as rising groundwater, tree deaths due to continuous inundation,
eutrophication of water resources and failure of infrastructure take many years
to become apparent. The timeframe noted in the SUGCD&WMP 2009 for
post-development monitoring is three years although a review of the drainage
and management plan is required to be undertaken within 10 years or earlier if
deemed necessary until development has occurred. Has any review of this plan
been undertaken?(7) If no to (6), why not and when will this review be undertaken?(8) Development
plans typically deal only with the footprint development will occupy and do not
include offsite impacts. The attitude adopted is that stormwater and
groundwater surplus to that deemed as required for environmental flows will be
managed by containment on site to be disbursed via a combination of
infiltration, biological processes, evaporation and release into receiving
waters at a rate to mimic pre-development flows. This process is failing within
the SUGC as evidenced by inundation and flooding of properties along the urban
fringe. What actions are being taken to address this situation and when will it
be remedied?
(1) What reviews have been
undertaken to determine the efficacy of drainage and water management
strategies within the Swan Urban Growth Corridor (SUGC)?
(2) What
studies have been undertaken to determine the efficacy of the infiltration
policy that underpins all drainage strategies within the Metro area with
particular reference to areas of high groundwater?
(3) Estimates
indicate somewhere around 100,000 trees have been removed to date with another
60,000 when development is completed within the SUGC south of Gnangara Road.
What studies have been undertaken to determine the impact of the removal of
thousands of mature trees within the district where high groundwater is
prevalent?
(4) What
studies have been undertaken to determine the efficacy of Water Sensitive
Design, (formerly Water Sensitive Urban Design), technologies within areas of
high groundwater?
(5) Foundation
documents such as the Swan Urban Growth Corridor Drainage and Water Management
Plan 2009 (SUGCD&WMP 2009) that provide the blueprint for Drainage
Strategies and Plans within the SUGC contain a number of measures to establish
the effectiveness of Local Water Management Strategies. These include
post-development monitoring as noted in SUGCD&WMP 2009 - 9.3 Monitoring strategy - Table 9-2 Assessment requirements of
development proposals – monitoring, for a period of three years. Has monitoring inline with these requirements
occurred for development or stages of development within the SUGC and where are
the results?
(6) Many
adverse impacts related to drainage strategies in areas of high groundwater,
such as rising groundwater, tree deaths due to continuous inundation,
eutrophication of water resources and failure of infrastructure take many years
to become apparent. The timeframe noted in the SUGCD&WMP 2009 for
post-development monitoring is three years although a review of the drainage
and management plan is required to be undertaken within 10 years or earlier if
deemed necessary until development has occurred. Has any review of this plan
been undertaken?
(7) If no to (6), why not and when will this review be undertaken?
(8) Development
plans typically deal only with the footprint development will occupy and do not
include offsite impacts. The attitude adopted is that stormwater and
groundwater surplus to that deemed as required for environmental flows will be
managed by containment on site to be disbursed via a combination of
infiltration, biological processes, evaporation and release into receiving
waters at a rate to mimic pre-development flows. This process is failing within
the SUGC as evidenced by inundation and flooding of properties along the urban
fringe. What actions are being taken to address this situation and when will it
be remedied?
undertaken to determine the efficacy of drainage and water management
strategies within the Swan Urban Growth Corridor (SUGC)?(2) What
studies have been undertaken to determine the efficacy of the infiltration
policy that underpins all drainage strategies within the Metro area with
particular reference to areas of high groundwater?(3) Estimates
indicate somewhere around 100,000 trees have been removed to date with another
60,000 when development is completed within the SUGC south of Gnangara Road.
What studies have been undertaken to determine the impact of the removal of
thousands of mature trees within the district where high groundwater is
prevalent?(4) What
studies have been undertaken to determine the efficacy of Water Sensitive
Design, (formerly Water Sensitive Urban Design), technologies within areas of
high groundwater?(5) Foundation
documents such as the Swan Urban Growth Corridor Drainage and Water Management
Plan 2009 (SUGCD&WMP 2009) that provide the blueprint for Drainage
Strategies and Plans within the SUGC contain a number of measures to establish
the effectiveness of Local Water Management Strategies. These include
post-development monitoring as noted in SUGCD&WMP 2009 - 9.3 Monitoring strategy - Table 9-2 Assessment requirements of
development proposals – monitoring, for a period of three years. Has monitoring inline with these requirements
occurred for development or stages of development within the SUGC and where are
the results?(6) Many
adverse impacts related to drainage strategies in areas of high groundwater,
such as rising groundwater, tree deaths due to continuous inundation,
eutrophication of water resources and failure of infrastructure take many years
to become apparent. The timeframe noted in the SUGCD&WMP 2009 for
post-development monitoring is three years although a review of the drainage
and management plan is required to be undertaken within 10 years or earlier if
deemed necessary until development has occurred. Has any review of this plan
been undertaken?(7) If no to (6), why not and when will this review be undertaken?(8) Development
plans typically deal only with the footprint development will occupy and do not
include offsite impacts. The attitude adopted is that stormwater and
groundwater surplus to that deemed as required for environmental flows will be
managed by containment on site to be disbursed via a combination of
infiltration, biological processes, evaporation and release into receiving
waters at a rate to mimic pre-development flows. This process is failing within
the SUGC as evidenced by inundation and flooding of properties along the urban
fringe. What actions are being taken to address this situation and when will it
be remedied?
(1) What reviews have been
undertaken to determine the efficacy of drainage and water management
strategies within the Swan Urban Growth Corridor (SUGC)?
(2) What
studies have been undertaken to determine the efficacy of the infiltration
policy that underpins all drainage strategies within the Metro area with
particular reference to areas of high groundwater?
(3) Estimates
indicate somewhere around 100,000 trees have been removed to date with another
60,000 when development is completed within the SUGC south of Gnangara Road.
What studies have been undertaken to determine the impact of the removal of
thousands of mature trees within the district where high groundwater is
prevalent?
(4) What
studies have been undertaken to determine the efficacy of Water Sensitive
Design, (formerly Water Sensitive Urban Design), technologies within areas of
high groundwater?
(5) Foundation
documents such as the Swan Urban Growth Corridor Drainage and Water Management
Plan 2009 (SUGCD&WMP 2009) that provide the blueprint for Drainage
Strategies and Plans within the SUGC contain a number of measures to establish
the effectiveness of Local Water Management Strategies. These include
post-development monitoring as noted in SUGCD&WMP 2009 - 9.3 Monitoring strategy - Table 9-2 Assessment requirements of
development proposals – monitoring, for a period of three years. Has monitoring inline with these requirements
occurred for development or stages of development within the SUGC and where are
the results?
(6) Many
adverse impacts related to drainage strategies in areas of high groundwater,
such as rising groundwater, tree deaths due to continuous inundation,
eutrophication of water resources and failure of infrastructure take many years
to become apparent. The timeframe noted in the SUGCD&WMP 2009 for
post-development monitoring is three years although a review of the drainage
and management plan is required to be undertaken within 10 years or earlier if
deemed necessary until development has occurred. Has any review of this plan
been undertaken?
(7) If no to (6), why not and when will this review be undertaken?
(8) Development
plans typically deal only with the footprint development will occupy and do not
include offsite impacts. The attitude adopted is that stormwater and
groundwater surplus to that deemed as required for environmental flows will be
managed by containment on site to be disbursed via a combination of
infiltration, biological processes, evaporation and release into receiving
waters at a rate to mimic pre-development flows. This process is failing within
the SUGC as evidenced by inundation and flooding of properties along the urban
fringe. What actions are being taken to address this situation and when will it
be remedied?
AnswerView source ↗
Answered
9 June 2026
Responded by
Leader of the House representing the Minister for Water
Response time
6 days
(1) As part of the planning process, proponents engage environmental, hydrological and engineering consultants to assess and determine the most appropriate drainage strategies to implement for the local site conditions. These assessments are documented in water management reports prepared and reviewed. in accordance with the Planning and Development Act 2005 and State Planning Policy 2.9: Water, to support structure planning, subdivision and development proposals..
(2) The infiltration of stormwater is only one aspect of the overall approach to managing water in the urban landscape.
State Planning Policy 2.9 and supporting technical documents like the Decision process for stormwater management provide guidance. In areas of high groundwater, urban development proponents use this to determine the appropriate way to manage water in the urban landscape by selecting the approaches that best suit the local site conditions. Typically, imported fill and/or appropriately designed stormwater and groundwater drainage systems, including subsoil drainage, are intended to be used to manage water (including management of poor drainage water quality) in the new urban form in a way that minimises changes to the surrounding environment, wetlands, waterways and other users.
(3) Potential local water impacts from tree removal are assessed and documented by environmental, hydrological and engineering consultants engaged by proponents through the preparation of water management reports, as part of the land planning process in accordance with State Planning Policy 2.9: Water.
(4) Studies have been undertaken in Western Australia and nationally relating to water sensitive urban design principles and approaches. In Western Australia, this includes multiple place-based studies and case investigations, including those delivered through the former Cooperative Research Centre for Water Sensitive Cities and its successor, Water Sensitive Cities Australia; case studies and fact sheets appropriate to local conditions by New Water Ways; and technical guidelines in the Stormwater Management Manual for Western Australia (DWER, 2022); Australian Rainfall and Runoff (Bell et al. 2019); Australian Runoff Quality – A Guide to Water Sensitive Urban Design (Engineers Australia 2006); and Adoption Guidelines for Biofiltration Systems (CRC for Water Sensitive Cities 2015).
(5) Responsibility to undertake post-development monitoring lies with developers and their environmental consultants who commit to the monitoring in their Sub-division and Development Water Management Reports; and local government authorities as part of their management of local drainage and public open space, in accordance with local water management strategies.
(6) No
(7-8) The drainage and groundwater management guidance in the Drainage and Water Management Plan (Department of Water 2009) remains fit for purpose for the sub-regional scale. The Department of Water and Environmental Regulation is currently engaging with the City of Swan and Department of Planning, Land and Heritage regarding the localised drainage and inundation issues, and technical assistance that may be required.
(2) The infiltration of stormwater is only one aspect of the overall approach to managing water in the urban landscape.
State Planning Policy 2.9 and supporting technical documents like the Decision process for stormwater management provide guidance. In areas of high groundwater, urban development proponents use this to determine the appropriate way to manage water in the urban landscape by selecting the approaches that best suit the local site conditions. Typically, imported fill and/or appropriately designed stormwater and groundwater drainage systems, including subsoil drainage, are intended to be used to manage water (including management of poor drainage water quality) in the new urban form in a way that minimises changes to the surrounding environment, wetlands, waterways and other users.
(3) Potential local water impacts from tree removal are assessed and documented by environmental, hydrological and engineering consultants engaged by proponents through the preparation of water management reports, as part of the land planning process in accordance with State Planning Policy 2.9: Water.
(4) Studies have been undertaken in Western Australia and nationally relating to water sensitive urban design principles and approaches. In Western Australia, this includes multiple place-based studies and case investigations, including those delivered through the former Cooperative Research Centre for Water Sensitive Cities and its successor, Water Sensitive Cities Australia; case studies and fact sheets appropriate to local conditions by New Water Ways; and technical guidelines in the Stormwater Management Manual for Western Australia (DWER, 2022); Australian Rainfall and Runoff (Bell et al. 2019); Australian Runoff Quality – A Guide to Water Sensitive Urban Design (Engineers Australia 2006); and Adoption Guidelines for Biofiltration Systems (CRC for Water Sensitive Cities 2015).
(5) Responsibility to undertake post-development monitoring lies with developers and their environmental consultants who commit to the monitoring in their Sub-division and Development Water Management Reports; and local government authorities as part of their management of local drainage and public open space, in accordance with local water management strategies.
(6) No
(7-8) The drainage and groundwater management guidance in the Drainage and Water Management Plan (Department of Water 2009) remains fit for purpose for the sub-regional scale. The Department of Water and Environmental Regulation is currently engaging with the City of Swan and Department of Planning, Land and Heritage regarding the localised drainage and inundation issues, and technical assistance that may be required.
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