5. Brookvale Creek - Warringah Council

Warringah Council
Creek Management Study - Appendix B
5. Brookvale Creek
The total area of the Brookvale Creek sub-catchment is approximately 450 ha. The
steep headwaters tributaries flow through remnants of natural bushland within Allenby
Park while immediately downstream of the parklands, the system has been modified
(i.e. piped and channelised) as a result of industrial and commercial development to the
east of Old Pittwater Road, including the Warringah Mall Shopping complex. Further
downstream within the Warringah Golf Course, the main channel flows through an
alluvial floodplain before joining Manly Creek immediately upstream of Passmore
Reserve. The combined system eventually discharges into the north-western section of
Manly Lagoon (Figures B5.1 and B5.2). The sub-catchment is over 40% impervious.
5.1 Values
Although the sub-catchment is over 40% impervious, high ecological values have been
retained in the reaches upstream of the industrial/commercial district with the
immediate natural catchment remaining largely intact. Allenby Park has been
previously described as a natural buffer to the surrounding residential development,
with significant scenic, environmental and biodiversity values and a range of habitats
such as Coachwood dominated rainforest along the boulder-lined creeks (Warringah
Council, 2000a). These upper reaches of Brookvale Creek contain good examples of
natural, moist creek line gully vegetation of the district, with moderate to high
connectivity, continuity and habitat quality in the riparian zone and floodplain. As a
result, native species richness and diversity is moderate to high and there is reasonable
potential for dispersal of native terrestrial fauna species. Special features include
waterfalls and rock overhangs, which provide high landscape value for the local
community (Warringah Council, 2000a).
Within Warringah Golf Course, vegetation connectivity and availability of refuge
habitat is low and there is currently poor potential for dispersal of native terrestrial
fauna species. However, these aspects are likely to improve over time as recent
rehabilitation activities continue. For example, native species richness has already
increased and weeds are considered to be largely under control. Early signs suggest that
the creek line vegetation is a good example of successful restoration of a highly
degraded system.
5.2 Water Quality
Despite the high ecological and landscape value of the upper reaches of Brookvale
Creek, water quality samples taken within Allenby Park exceeded the recommended
guidelines for all nutrient forms. In particular, the concentration of dissolved
phosphorus was the highest of all sites sampled during the study. The faecal coliform
count was also the highest recorded and suggests that the upper reaches are unsuitable
Status – Final B16 March 2004
Project Number – 831/000070A
Our Ref − Final_Appendix_B_Sub-catchment_Summaries

ManlyCreek
ManlyCreek
Brookvale
Creek
Brookvale
Creek
Dee
Dee
Manly
Reservoir
322488
322488
323488
323488
324488
324488
325488
325488
1261471
1261471
1262471
1262471
1263471
1263471
WarringahCouncil
WarringahCreek
ManagementStudy
BROOKVALECREEK
FigureB5.1
Source:Contours,Imagery,DCDB,Lga
andCatchmentboundariesfrom
WarringahCouncil;Lgaboundaries
basedon1:100,000Topographicdata.
DrainageandriparianbuffersfromMWH
Date:March03,2004
Projection:ISGZone56
OverviewMap
DeeWhyBeach
FreshwaterCreek
BurntBridgeCreek
Middle
Harbour
Wheeler
Creek
DeeWhy
LagoonNorth
DeeWhy
LagoonNorth
DeeWhyLagoonSouth
Duffys
Creek
Oxford/
Snake
Creek
Narrabeen
Foreshores
Narrabeen
Foreshores
Brookvale
Creek
Collaroy
Greendale
Creek
Frenchs
Creek
McCarrs
Creek
Bantry
Bay
Cottage
Point
Bare
Creek
South
Creek
Carroll
Creek
Manly
Creek
Middle
Creek
KieransCreek
DeepCreek
SmithsCreek
ProducedinArcMap8byMWHEnvironmentalDivision
COPYRIGHT-MAPNOTTOBEREPRODUCEDINPARTORFULLWITHOUTTHEEXPRESSAUTHORISATIONOFMWH
MARCH03,2004
\\PROJECTS\831-000070\GIS\SALL_E\WARRINGAH\BROOKVALE_A3P.MXD
0 125 250 375 500
Meters
Legend
CadastralBoundary
Creekoropenchannel
EngineeredChannel
AdjacentCatchmentBoundary
WarringahShireBoundary
NationalPark
RiparianZone
RiparianBuffer
Contour(2minterval)

ManlyCreek
ManlyCreek
Brookvale
Creek
Brookvale
Creek
Dee
Dee
Manly
Reservoir
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1261459
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1262459
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1263459
WarringahCouncil
WarringahCreek
ManagementStudy
BROOKVALECREEK
FigureB5.2
Source:Contours,Imagery,DCDB,Lga
andCatchmentboundariesfrom
WarringahCouncil;Lgaboundaries
mayhavesomeminormisalignments.
DrainageandriparianbuffersfromMWH
Date:March03,2004
Projection:ISGZone56
OverviewMap
SmithsCreek
DeepCreek
KieransCreek
MiddleCreek
Manly
Creek
CarrollCreek
South
Creek
BareCreek
Cottage
Point
BantryBay
McCarrs
Creek
FrenchsCreek
Greendale
Creek
Collaroy
Brookvale
Creek
Narrabeen
Foreshores
Oxford/
Snake
Creek
Duffys
Creek
DeeWhyLagoonSouth
DeeWhy
LagoonNorth
Wheeler
Creek
Middle
Harbour
BurntBridgeCreek
FreshwaterCreek
DeeWhyBeach
ProducedinArcMap8byMWHEnvironmentalDivision
COPYRIGHT-MAPNOTTOBEREPRODUCEDINPARTORFULLWITHOUTTHEEXPRESSAUTHORISATIONOFMWH
MARCH03,2004
\\PROJECTS\831-000070\GIS\SALL_E\WARRINGAH\BROOKVALE_A3.MXD
Legend
RiverStyles
CadastralBoundary
Channalisedvalleyfill(CVF)
Confinedwithoccasionalfloodplainpockets(CFP)
Estuarine/tidal(ET)
Gorge(GO)
HangingSwamp(HS)
Lowsinuositysandbed(LS)
Partlyconfined,bedrockcontrolled
withdiscontinuousfloodplain(PCF)
SteepHeadwater(SHW)
Unclassified(U)
Urbanmodified(UM)
Urbanpiped(UP)
n.a
CatchmentBoundary
WarringahShireBoundary
NationalPark
RiparianZone
RiparianBuffer
Contour(2minterval)
0 125 250 375 500
Meters

Warringah Council
Creek Management Study - Appendix B
for secondary contact recreation. The concentration of biological oxygen demand was
also relatively high, although suspended solids levels were low. Monitoring results
recorded by Laxton (2000) indicate that the concentration of all parameters are typically
lower downstream within the Golf Course, although total and dissolved nitrogen and
total phosphorus levels still exceed recommended guidelines.
Likely sources of pollutants within the sub-catchment are stormwater runoff from
residential and industrial areas within Beacon Hill, Allambie Heights, Brookvale and
North Manly. Major sources of faecal contamination would include domestic animal
waste in residential areas and other wildlife within the parklands. The results suggest
that the bushland surrounding the upper reaches provides little attenuation or trapping of
pollutants.
5.3 Risks
Within Allenby Park, weed invasion is very minor and confined to specific areas.
However, if these weeds are not controlled, the extent of infestation will gradually
increase and the existing values of the natural system would eventually be lost. Urban
nutrient enrichment (i.e. runoff and garden-refuse dumping) and alterations to
hydrology are also major risks, particularly in relation to rainforest vegetation
communities adjacent to the creek lines within Allenby Park (Warringah Council,
2000a). The reintroduction of weeds from unrestored sections also poses a threat to
areas revegetated within Warringah Golf Course.
5.4 Recommendations
Several reaches within Allenby Park are considered excellent candidates for community
projects. In particular, complete weed eradication may be a possibility at these sites due
to the minor extent of current infestations. This should be coupled with a community
education program to prevent the escape of exotic garden species into the natural
system. Adequate maintenance of these upper reaches is required to prevent weed reinvasion
in downstream reaches that are already being managed (i.e. Warringah Golf
Course).
Status – Final B17 March 2004
Project Number – 831/000070A
Our Ref − Final_Appendix_B_Sub-catchment_Summaries