porirua harbour seminar series - pres 4 - gwrc presentation on porirua stream condition

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

porirua harbour seminar series - pres 4 - gwrc presentation on porirua stream condition

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