Porirua City Council Draft Significance and Engagement Policy
Porirua Harbour Seminar Series - Pres 4 - GWRC Presentation on Porirua Stream Condition
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Transcript of Porirua Harbour Seminar Series - Pres 4 - GWRC Presentation on Porirua Stream Condition
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7/29/2019 Porirua Harbour Seminar Series - Pres 4 - GWRC Presentation on Porirua Stream Condition
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Porirua
Stream
A major artery ofA major artery ofPoriruaPoriruaHarbourHarbour
Juliet Milne, 28 October 2009
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Outline Catchment overview
Monitoring &investigations water quality
stormwater
ecology
Key threats
Management issues
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Catchment overview Catchment area: 55 km2
5 major tributaries Belmont, Takapu, Stebbings,
Mitchell & Kenepuru
Key flow statistics mean annual flow: 783 L/s
median flow: 373 L/s
mean annual low flow125 L/s
mean annual flood: 35 m3
/s
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Monitoring
Rainfall & stream flow
Water quality oxygen, temperature, pH
clarity, turbidity & TSS
nutrients & E. coli
heavy metals
Ecological indicators
Algae, invertebrates & fish
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E. coli bacteria counts Glenside
10
100
1,000
10,000
100,000
Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09
E.coli(
cfu
/100mL)
Glenside
Action
Alert
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E. coli bacteria counts Glenside & Wall Park
10
100
1,000
10,000
100,000
Sep-03 Sep-04 Sep-05 Sep-06 Sep-07 Sep-08 Sep-09
E.coli(
cfu
/100mL)
Glenside
Wall Park
Action
Alert
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ANZECC Lowland TV
ANZECC Upland TV
median
Lower quartile
Upper quartile
Nitrate nitrogen by key landcover classes
Upland
native
forest
Lowland
native
forest
Lowland
pastureLowland
Urban
Porirua Stream
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Jan 2007Sept 2003
Clarity(m)
Porirua Stream clarity over time
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Sediment load: 0.0126 kg per minute
TSS=1.5 g/m3, flow=0.14 m3/s TSS=98 g/m3, flow=0.329 m3/s
Sediment load: 1.93 kg per minute
Porirua Stream suspended sediment
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Stormwater
investigations1) Wet weather stream flows
sediment & heavy metals
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0.1
1
10
100
Jan-06 Jul-06 Jan-07 Jul-07
Concentration(ug/L)
Total Copper
Diss. Copper
Chronic toxicity
Acute toxicity
Copper concentrations in Porirua Stream during wet weather
flows
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Copper concentrations in Porirua Stream during wet weather
flows
0
1
2
3
4
5
6
7
89
10
Jan-06 Jul-06 Jan-07 Jul-07
Co
ncentration
(ug/L)
Acute toxicity
Chronic toxicity
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Total instream contaminant load (kg)
Date of event
Estimated
runoff volume(m3) TSS Diss Cu Total Cu Diss Pb Total Pb Diss Zn Total Zn
27 March 2006 11,130 189 0.10 0.09 0.01 0.06 0.51 0.52
7 April 2006 9,560 76 0.05 0.06
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Zinc & DDT key contaminants
PAHs Kenepuru Streamabove SH 1
Little fine sediment present
Fine sediment and its
associated contaminant load is rapidly flushed throughthe system into Porirua
Harbour
2) Streambed sediment quality
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What about thestream life?
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Invertebrates indicators of stream health
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Stream monitoring sites & key land cover classes ranked from highest to lowest aquatic health
Decreasing macroinvertebrate index scores
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Invertebrate health vs land-use
Indigenous Forest Pasture Urban
MCI(m
eanscore)
40
60
80
100
120
140
160
Excellent
Good
Fair
Poor
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Bugs dont like concrete!
Excellent
Moderate
Poor
01
2
3
4
5
6
7
0 10 20 30 40
Impervious cover (%)
Inv
ertebrate
health
score
Excellent
Moderate
Poor
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Banded kokopu
Koaro
Eel
Giant kokopu
Inanga
Takapu Stream tributary
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Monitoring shows:
elevated nutrients& faecal bacteria
stormwater-derivedtoxicants present
passableinvertebrate health
relatively highnative fish values
Room for improvement
Stream state summary
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Discharges sewage leaks& overflows, industrial
wastes, silt from earthworks/erosion, stormwater
Key threats
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Key threats.
Filling in/piping of smallstreams & gullies
Increased runoff
Bank protection works& drain clearance
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Key threats
Loss of habitat
Loss of function(slow, cool, clean
water)
Loss of future use
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Management issues
Sediment, nutrient
& contaminantinputs
control at source
slow runoff down!
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Management issues Stream habitat
minimise streamloss (pipes, culverts)
restore riparian
margins protect & enhance
instream habitat
provide for fishpassage
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What you docanmake a difference