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Healthy Rivers CSG 2 July 2015

Waikato River Hydrology Presentation

Lake Taupo

David Payne

Waikato Hydro System Catchment

Drought and Flood conditions

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Lake Taupo

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Lake Taupo catchment

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Lake Taupo water level, rainfall and flow stations

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Lake Taupo mean Monthly inflow

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Taupo lake level ranges

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Top 5 Lake Taupo facts

> The available lake Taupo storage is 855 Mm3 (1.4m range and 611 Km2 Lake area)

> The available storage is used on average 5 to 6 times a year

> The size of the hydro dams and reservoirs is such that the water obtained as a result of rainfall is

able to be used for generation purposes

> Mighty River Power has operated the Waikato Hydro Scheme since 1998 and during that time the

annual inflow versus outflow of Lake Taupo has not varied by more than 5%.

> The aim is to have the lake around 356.8 to 357.0 masl at the start of the year for drought

contingency purposes.

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Waikato Hydro System

Catchment

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Waikato Hydro System catchments

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Waikato Hydro System dam elevations

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Total storage Lake Taupo 93%Total Storage WHS 7%

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Modelled dam residence times

> The dam residence time below are based on Opus modelling for the report “Waikato Catchment

Water Quality Model” (2000), Rutherford etal

> Residence time for a natural catchment from Taupo to the sea is 5 to 6 days

> Residence time for low flows to pass through the hydro system (Taupo to Karapiro) is 30 days, from

Taupo to the sea it is 35 days

> Residence time for mean flows to travel from Taupo to the sea is 23 days

> Residence time for high flows to travel from Taupo to the sea is 15 days

> ENVCO conducted some flow velocity measurements for the hydro system

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Waikato Hydro System inflow versus Karapiro dam outflow

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0

50

100

150

200

250

300

350

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Flo

w (

m3 /

s)

Months

WHS Inflow

Karapiro Outflow

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Operation under

drought conditions

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Lake level under drought conditions

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Operation under flood

Conditions

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Taupo inflow and outflow

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1357

998960 986

1024

206

315 293 318 317

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1958 1998 2001 2004 2011

Flo

w (

cum

ecs

)

Flood Years

Inflow

Outflow

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Lake Taupo flood inflow, outflow and level graph

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20-Jan-2011 25-Jan-2011 30-Jan-2011 4-Feb-2011

0

200

400

600

800

1000

1200

357.00

357.08

357.17

357.25

357.33

357.42

357.50

Flo

w

(c

um

ec

s)

Flo

w

(c

um

ec

s)

Lake Taupo Total Inflow (m3/sec)Lake Taupo Total Outflow (m3/sec)Lake Taupo Lake Level (m)

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Waikato Hydro System inflow and Karapiro outflow

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1094 1120

661

897

631580 566 551

0

200

400

600

800

1000

1200

1998 2004 2008 2011

Flo

w (

cum

ecs

)

Flood Years

No WHS

KPO Outflow

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Waikato Hydro System inflow and Karapiro outflow (2011 event)

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22-Jan-2011 24-Jan-2011 26-Jan-2011 28-Jan-2011

0

100

200

300

400

500

600

700

800

900

1000

Flo

w

(c

um

ec

s)

Flood Information No WHS Flow CertifiedKarapiro Total Outflow (m3/sec)