Pakuranga Creek Master Plan
Pakuranga Creek Master Plan, Opus International Consultants Ltd, 2001.
Introduction | Site Description | Management Issues | Management Strategies
Introduction
This Master Plan has been prepared by Opus International Consultants (Opus) for Manukau City Council (MCC) to provide options for the long-term management and restoration of Pakuranga Creek. This Master Plan covers the upper stream area of Pakuranga Creek from William Green Domain and Casuarina Road downstream to Cascades Road.
Pakuranga Creek fulfils a variety of functions:
- As a conveyance of stormwater discharge
- As an integral feature in two parks
- As a community amenity
- For passive Recreation
- As a habitat for fish, birds and flora
- Providing linkage to Cascades, the greater community, other sections of the stream network and the Tamaki estuary
However, the Creek has been highly modified from its original condition. Meanders have been straightened, channelised and/or lined to facilitate maintenance and accommodate flood flows. Planting in the reserves adjacent to the Creek has generally been ad hoc, if at all, and orientated to the reserve rather than the Creek. This planting shows little consideration of habitat values or opportunities for aesthetic or other enhancement of this once natural system.
Manukau City Council is aiming to develop a better quality riparian and stream environment as an integral element of the landscape while fulfilling storm water catchment needs. This will include introduction of stormwater treatment and erosion control and riparian planting strategies to improve water quality and instream and riparian habitat. Pakuranga Creek discharges to the Tamaki Estuary so improvements in water quality are expected to result in regional improvements as well.
Because Pakuranga Creek flows through several greatly used
reserve areas, another key aim of the Master Plan is to foster
community participation and recreational use.
A Resource Consent application for Consent to Discharge has
been lodged with the Auckland Regional Council (GHD, 2001).
Included in the application is a proposal for stormwater treatment
ponds as one of the options to remove sediment prior to discharge.
This Master Plan is intended to be consistent with the Consent
Application and will form the basis of future applications
to Infrastructure Auckland, for funding of recommended stormwater
treatment projects.
It is important to remember that the transition to a more
sustainable, ecologically valuable condition will take time,
both to implement and to establish. The Master Plan sets out
priorities for this ongoing process.
Site Description
The Pakuranga Creek lies :n central Pakuranga and discharges
to the Tamaki Estuary.
The Creek passes through several reserves, including Llovd
Elsmore Park and William Green Domain before joining with
the Cascades Walkway tributary and flowing into the Tamaki
Estuarv. The Creek also borders residential and commercial
areas, notably the large Highland Park Shopping Centre. Pakuranga
College also borders the eastern side of the Creek upstream
of Pakuranga Road.
As discussed previously much of the channel has been altered from its original condition. The left hand tributary above Pakuranga College has been lined with a low timber retaining wall. Downstream the base of some channels have been lined with concrete. The ARC maintains a monitoring flume just upstream of Moonys Bridge.
Catchment Management Issues
The upper Pakuranga Creek is part of the Moonys Bridge Catchment (No. 675), which is about 506 ha in area. Vegetation indicates that tidal influence extends from the Tamaki Estuarv upstream to just above Cascades Road.
Flood flow rates have been predicted according to the graphical methods presented in the ARC Technical Publication 108, which is based on the U.S. Soil Conservation Service methodology. The Consent Application states that approximately 52% of the subcatchment is impermeable with a Curve Number of 89, which is characteristic of a highly urbanised catchment. The Consent Application gives the following flow data:
| Annual RecurrenceInterval (ARI, years) | 2 | 5 | 100 |
| Annual ExceedanceProbability | 50 | 20 | 1 |
| Peak Flow Rate (m3/s) | 18.6 | 27.8 | 57.6 |
| Runoff Depth (mm) | 54.6 | 82.5 | 170 |
Problem flooding has been identified in several areas of the catchment, but they are upstream and away from the Creek. Nevertheless, during storm events, the Creek overflows its banks and inundates adjacent reserve land.
Stormwater runoff, particularly from urban areas, contains a variety of pollutants. In addition to minor sediment and pollutants from residential areas, other potential contributors of pollutants to the Creek include:
- Commercial parking areas and high volume roads which contribute sediment, hydrocarbons and metals
- A former landfill at Bells Road which is thought to contain non-household refuse and may contribute minor leachate
- The following MCC sewerage pumping stations
- Pakuranga College/Highland Park (No. 34)
- Aviemore Drive (No. 49), this has been identified as a known overflow point
- Cascades Road (No. 69
MCC has previously proposed stormwater quality ponds along Pakuranga Creek to reduce the amount of sediment and other pollutants being discharged to the Tamaki Estuary. This Master Plan incorporates and builds on those previous proposals.
Vegetation and Landscape
Pakuranga Stream flows through predominately grassed reserve areas. Streamside planting includes a mixture of exotic and native vegetation. Exotic tree species include willow, oak, pine and macrocarpa. Native tree species are limited and are restricted to relativelv newlv planted specimen trees in grass. These are generally, kahikatea, totara and pohutukawa. The western uplands adjacent to the stream in central Lloyd Elsmore Park have been planted in native shrub species, about 10 metres from the stream edge. This native planting mix of flax, manuka and cabbage tree.is a little removed from the stream and the straight line of planting relates more to the fields than the stream.
The draft Management Plan of Lloyd Elsmore Park (1994) describes early vegetation planting as:
"Many of the larger trees that have been planted are fast growing species, which were chosen for their rapid effect to assist in the establishment of the park, rather than for their aesthetic value e.g. Casurinas, Eucalyptus, Poplars. Due to the ongoing implementation, with a variety of different approaches, the tree planting lacks a defined structure or character at this stage. Similarly much of the shrub planting indicates more of a functional role with Ngaios, Pampas grass and Flax prominent."
Section 3 provides a "walk" downstream via a photo essay. The commentary identifies notable features, vegetation themes, potential pond sites, and erosion areas.
Ecology
The portion of Pakuranga Stream that makes up this study, is generally very open with most stream edges consisting of open grass land. Occasional trees line the stream to the north, large oak trees shade a central section of the stream and the streamside is very open to the south.
Fish passage is not encouraged by this lack of shading and overhanging vegetation which results in water temperatures that are too high. However, the existing culverts do not appear to fullv restrict fish passage up until the pedestrian bridge upstream of Pakuranga College and the concrete dish channel just downstream of the Bucklands Road culvert. As discussed later, this Master Plan presents strategies for enhancing fish passage along the stream.
A recent ARC report on Urban Streams (ARC, 2001) samples Pakuranga Creek amongst other sites. Pakuranga Creek falls into two of the studies categories - low gradient coastal streams, and degraded water quality streams.
It finds that populations of Imanga, common smelt, common and redfin bully, giant and banded kokopu, short and long fin eel, may all be found in Auckland's low gradient coastal streams. The reports objectives for this category include reduction in suspended sediment load, improvement of riparian vegetation to provide shading and habitat and to allow bank reinforcement on stream bends.
Unfortunatelv the Pakuranga Creek also falls into the category degraded water quality, the JCreek is specificallv referred to as having generally low quality. Degraded water streams only support one fish species - short fin eel. The first objective, then, is to improve water quality.
Cultural Heritage Values
Maori and European heritage of the local area is currently recognized and expressed through displays within the Historic Village. The Historical Village lies in the centre of Llovd Elsmore Park, adjacent to the Creek. Buildings have been relocated to the site and include displays on Maori and European history. Consultation with management of the Historic Village may highlight possibilities to strengthen links between the Village and the area of the stream directly adjacent to the Village. Potential exists to improve interpretation of the cultural value of the Creek following consultation with iwi, and other community interest groups through information boards at key points along the stream.
Public Recreation
The Lloyd Elsmore Park provides most of the active recreation opportunities in the region and is characterized by numerous playing fields and other broad open spaces. It also provides for other diverse activities including a swimming pool, pond, indoor sports areas and Historic Village.
The Park provides direct access from residential areas to shops, schools and recreational facilities. Completion of linkages would also be an advantage as a means of reducing transport needs of the area.
At present, a walkway exists for most of the stream length. This offers the community the opportunity to experience the stream environs first hand. However, the walkway has little integration with vegetation or the Creek and opportunities exist for enhancing this amenity to provide a fuller recreational experience.
Little information is presently on display about the nature and extent of the stream. New signage can be developed to explain and highlight features of the area.
Soil and Erosion
With the exception of free-draining granular volcanic soil in the northern part of the catchment, soils in the area are generally poor draining volcanic and alluvial sediments and weathered mudstone and sandstone.
A number of sites along the creek have experienced significant erosion. These areas are highlighted in sections 3 and 4. Erosion of stream banks leads to potential loss of vegetation, increased loading in the Creek, reduction in water clarity and reduction of a stable streamside environment.
Section 4 Existing Vegetation and Erosion>>
Management Issues
General
Site walks along the Creek identified a number of problem areas where physical features inhibit the natural appearance or function of the stream. It also highlighted opportunities for enhancing the streamside riparian environment and identified areas where wetlands and ponds could be introduced to enhance habitat and improve water quality.
Table 1 identifies these concerns and identifies generalised strategies for addressing them. Specific strategies are then detailed in Section 5.
Table 1- Pakuranga Creek Management Issues and Options for Improvement
| Watercourse Management Concern | Issue | Option for Improvement |
|---|---|---|
| Ecological Improvement |
||
| Fish Passage |
|
|
| Concrete
structures in streambed |
|
|
| Weed Species |
|
|
| Landscape Visual |
|
|
| Erosion | ||
| At culverts |
|
|
| Channel Slumping |
|
|
| At outside bend of meanders |
|
|
| Hvdraulic Issues | ||
| Undersized culvert at Bucklands Road |
|
|
| Failure of timber retaining walls |
|
|
| Storm Water Quality | ||
| Turbidity in Runoff |
|
|
| Maintenance |
|
|
| Amenities & Recreation |
|
|
Management Strategies
Proposed Management Strategies
Table 2 presents specific strategies that could be implemented along the Creek. Figure 3 presents the Master Plan for the Creek while concept plans for the strategies are included in Appendix C. Appendix D details estimated costs for the proposed strategies.
Figure 3
Pakuranga Stream Improvement (Section 1)>>
Figure 3 Pakuranga Stream
Improvement (Section 2)>>
Future development of the stream margins needs to consider the wavs in which impacts from the catchment's land use can be minimised and how to maximise the opportunities to enhance habitats. Ecological enhancement will take place with the planting of native wetland and riparian vegetation, shading of the watercourse and stabilisation of the stream banks.
Habitat and stormwater quality can be improved with the introduction of stormwater ponds and wetland svstems. Three such systems are proposed.
Table 2 - Pakuranga Creek Proposed Management Strategies
| Management Stragegy | Description | Feature | Constraints | Estimated Cost | Priority |
|---|---|---|---|---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Storm water Quality Marsh and Ponds | |||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Other | Varies | Varies; Incorporate with above projects as they are implemented | |||
|
|
|
|
|
|
|
|
|
|||
New Planting
The viability of the stream as an ecological habitat would
be greatly enhanced if the streamsides contained a continuous,
wide band of vegetation that offered habitat and shade to
the water. Since dense margin planting is often at cross purposes
to maintaining hvdraulic efficiencv, careful selection of
plant species and placement of planting is very important.
"
New planting schemes should incorporate the following objectives;
- To be low maintenance.
- To visuallv enhance character and arnenitv of stream.
- To reflect the local character of the area.
- To improve native habitat & to provide a source of food for birds.
- To improve water qauaiity and bank stabilisation.
- To provide for the saren- of park users.
A clear hierarchy of vegetative areas will allow hydraulic efficiency to carry awav storm flows as well as helr to simplify streamside maintenance. Mowing can operate to a defined edae that is manageable in terms of steepness and horizontal alignment. The next portion of the bank can be planted in terrestrial, shading vegetation at the top of the bank, leading down to riparian margin wetland planting. This margin planting is made up of species normally found in bog conditions that will tolerate wet soils, drving out over summer and occasional inundation of stream water. In steeper banks, shade trees at the top of the rank can allow the establishment of low ferns.
Suggested native shade species are hoheria, mapou, kanuka, manuka, kohekohe, wheki, hangehange and mamangi (the latter four species are particularly relevant to Manukau region). Suggested stream bank planting are Carex spp, Baumea spp. and Juncus spp. Cabbage tree and flax can supplement this mix, but should be located on the upper slopes so as not to impede water flow.
Stabilisation techniques applied to key erosion points, including bank protection and provision of outlet protection to culverts, will contribute to permanent riparian margin and permanent plant habitats. Weed removal will be necessary in the first years, as the plants establish, but thereafter, the planting will form a closed canopy that will block out light and deter weed growth. Maintenance practices within parks will also need to respect the integrity of this vegetation.
Ponds and Wetlands
Three areas have been identified for the establishment of
marsh and pond areas to develop as habitat and to provide
stormwater treatment. These areas can be developed to be visually
attractive and provide linkages to the greater Tamaki Estuary.
All ponds will have similar design considerations including
providing safe batters, access at key points for periodic
sediment removal, provision of fish passage, etc.
William Green Domain: A pond and wetland svstem of approximately 3,400 m2 is proposed for the William Green Domain. It is estimated to provide approximately 45% sediment removal from discharges from the approximately 98 ha upstream catchment. A pond in this area has been proposed in the application for Consent to Discharge for the catchment.
The Draft Management Plan (1996) for the William Green Domain proposed an offline pond of similar size, but also proposed piping and filling a portion of the stream to develop as a sport field.
This pond as proposed is to be an in-line pond for the following reasons:
- the discharge will have already entered the Creek system by this point
- the existing Creek is alreadv highly modified with little existing habitat value
- the pond is intended to provide instream habitat
- an in-line pond would require the least excavation and be the most cost effective.
However, an offline ponu cuald be developed at the site, although it would have large excavation requirements which would increase costs and may need to be sited in areas scheduled for other uses.
Since the pond is relatively small a forebav is not proposed. The pond would consist of areas of open water with perimeter wetland planting. The sediment accumulated within the pond would require periodic removal.
College Pond: This wetland and pond svstem is similar to that described above. It is estimated to be approximately 40% efficient in removing sediment from the discharge from the 200 ha catchment which drains into the left-hand tributary of the Creek.
While a high-flow bypass channel is not proposed for either the Domain or the College pond, with careful design, flood plain overbank areas can be provided so that velocities within the ponds remain low and sediment is not resuspended.
Llovd Elsmore: The Lloyd Elsmore wetland and pond system is to consist of a series of pond and marsh areas, just downstream of the Historic Village. It would include open water and benched wetland planted areas and some areas would be tidally influenced which would provide biological and visual linkages with downstream areas as well as improving the settling of sediment. A series of low weirs would allow development of pond and wet areas that would include fish passage while not causing- flooding of adjacent properties. At least one of the weirs would include a throttled outlet to allow significant ponding (and sediment removal) during some storm events, but which could be overtopped during extreme storms.
This pond and wetland system differs slightly from that proposed in the application fro Consent to Discharge the catchment. The amount of excavation proposed for this system is much less, which will make the project more economical and easier to develop with respect to geotechnical issues. Also a weir is not proposed for the reach below the Cascades due to existing habitat values, size of pond volume relative to size of two large catchments, and to maintain brackish conditions similar to the existing.
The sediment removal efficiency on a volume basis (average depth =0.75m) has been estimated at 42% for the 500 ha'upstream catchrnent. Actual removal rates would be expected to be higher though due to entraining of particles by vegetation and flocculation in the brackish environment. Overall sediment removal from the three proposed ponds would be approximately 45 7.
Recreational and Amenities
Walkways: At present. a walkway exists for most of the stream
length. This offers the communitv the opportunity to experience
the stream environs first hand. This walkway could be further
developed in the following ways:
- Make minor modifications in the path alignment at key points. This is to reduce the linearity and introduce `meanders' that reflect a stream course.
- Align the path closer to the stream at improve the experience and appreciation of the stream environment.
- Look to opportunities to bridge the stream. Further downstream, opportunities wiill be limited because of the requirement of a structure to withstand water flows. However, the existing pipe bridge could be utilised as a means of crossing the stream by retrofitting a wooden bridge structure over the pipe structure.
- Slight lines will always be a design factor to ensure safety considerations of Park users are met.
The walkway should also be expanded to connect the existing Cascades walk to the Historic Village area.
Signage: Little information is presently on display about the nature and extent of the stream. New signs can:
- Provide information about the stream and catchment, the ecological process of the stream and the background to new developments and treatments, such as the riparian planting and shaping of the stream banks
- Provide information about the development of stormwater ponds and their role in water quality improvement / flood management
- Create a sense of identity to the stream margins through the signs themselves and a consistent design treatment. This will contribute to a sense of ownership by the community.
- Provide information at specific points along the route
- Provide direction
Recreation Features: Recreational features can be incorporated along the route in the form of picnic tables, seating and overlooking areas to the stream and new ponds.
Special treatment is suggested at the proposed pond weir by Pakuranga College. Stone can be incorporated and designed in aquatic themes. Public art displays could be established in the Historic Village area that would reflect the special character of that area.
Stream Maintenance
Mowing: A clear hierarchy of maintenance
areas will help to simplify streamside maintenance. Ivlowing
can -operate to a defined edge away from the stream that is
manageable in terms of steepness and horizontal alignment.
. This will ensure good riparian vegetation establiShnnent
and reduce maintenance.
In areas where riparian enhancement will not be implemented in the short term, it may be appropriate to establish a one to two metre band of grass adjacent to the stream that should not be mowed. This would provide straining and trapping of sediment in overland tiow, aid in reducing bank slumping, and also reduce the amount of clippings that may find their way into the stream.
Weed Control Programme: A weed control programme should be developed to ensure the survival of newplanting, the maintenance of a high aesthetic standard and the deterioration of the quality of the stream ecology. This will provide a general structure and setting of standards that will establish a consistency in approach to the stream environment. The programme should identify specific weed species, location and means of eradication. All methods will need to respect the health and safety of the communitv, the and the existing plant and wildlife habitats.
Conclusion
Pakuranga Creek presents a unique opportunity to re-establish
viable habitat. While it has been highly modified from its
natural condition, both physically and in terms of water quality,
unlike many watercourses, it has not been fully piped or channelised
with concrete. Because the Creek is situated in reserve land,
restoration and stormwater managemer t st-ategies are not
as constrained bv existing land use and availabilitv as in
many other urban areas. However, the process will onlv be
accomplished over a long time period and with a good deal
of money. Additionally, natural systems in urban areas will
require ongoing maintenance that is sensitive to restoration
objectives.
Because future improvents will take time, a staged approach to improvements will be necessarv. To assist in this strategy, proposed actions have been given priorities as shown Table 2. High priority is attached to streamside enhancement planting, culvert protection and protection of erosion at meanders. Medium priority is attached to the introduction of the three pond and wetland systems. Low priority is attached to channel easing and planting. Planting and other improvements to the walkway system, new signs and furniture can take place on an ongoing basis. Appendix A includes a programme to illustrate how these strategies could be implemented over time.
Because the Creek adjoins residential neighbourhoods andlies within well utilised recreational areas, there is expected to be ample support for development and and implementation of the restoratio strategies. There is opportunity for community involvement both in the planning as well as implementation stages of the project. Planting, particularly, can be an important recreational activity in itself.
t is expected that this master plan will only be the starting
point in an iterative development process. Community consultation
and involvement with these and all aspects of this Master
Plan is considered integral to the success of the improvements
to Pakuranga Creek.