Integrating Groundwater Modelling and River Ecology

Dean Olsen1, Roger Young1, Tim Davie2, Timothy Hong3 and Joseph Thomas4

1 Cawthron Institute, 2 Landcare Research, 3 Geological and Nuclear Sciences, 4 Tasman District Council.

o Groundwater modelling in Upper Motueka• Predicts surface water-groundwater

(SW-GW) exchange

o Cold upwelling groundwater• Refuge for aquatic life during low flows

Study area

Motueka

River

Wan

gape

kaRi

ver

Tadm

orRiv

er

Study area

Mot

upik

oR

iver

N

Tapawera

Upper MotuekaCatchment

Groundwater-river modelling

Biggs

Oldham's Tam

or R

iver

Motueka River

River gauaging sites undertaken byTDC on 09/02/2002

Above Wangapeka confluence

Above Glenrae Stream

Letterbox "Smith"

BelowTapawera

bridge

Tapawera bridge

Above Tapawera bridge/Rogers

Groundwater monitoring sites

o 3d finite element model developed in using FEFLOW

o Currently only steady-state

Model predictions

AboveTapawera

bridge/Rogers

Tapawera bridge

Below Tapawerabridge

Letterbox "Smith"

Above GlenraeStream

AboveWangapekaconfluence

36806 m3/driver gain

85708 m3/driver loss

62812 m3/driver gain

16243 m3/driver loss

8640m

3 /d

river

gain

W14

W25

W22

W36 W23

W28

W10

W20

W17

W40

W6

W15

W e ll ID

A bstra ct ion ra te use d (m 3/da y)

6 1500 10 257 .4 11 257 .4 14 2802 .6 15 193 .2 16 308 .4 17 244 .2 20 180 22 1234 .2 23 784 .2 25 385 .8 28 630 33 900 34 360 36 90

40 254 .4

Tam

or R

iver

valle

y

Motueka River valley

GainingLosing

Key

• Predicts location and magnitudes of exchanges between river and groundwater

Model predictions

Tapawera bridge

Below Tapawerabridge

Letterbox "Smith"62812 m3/driver gain

16243 m3/driver loss

40m3 /d

in

W23

W28

W10

W20

Motueka River valley

GainingLosing

Key

Tadmor River

GAINING REACH

LOSING REACH

LOSING REACH

Predictions

Variations in SW-GW exchange will affect thermal patterns in the river

Diel fluctuations in temperature:Gaining < losing reaches

Maximum daily temperature:Gaining < losing reaches

Methods

• 8 data loggers:• 3 gaining reaches• 3 losing reaches• 1 spring• 1 groundwater bore

• Logging 30 min intervals from early 2006

Year2006.1 2006.2 2006.3 2006.4 2006.5 2006.6 2006.7

Wat

er te

mpe

ratu

re (o

C)

0

5

10

15

20

25

Gaining reachLosing reach

Spring Creek (MRT ~14 months)Groundwater (MRT ~3y)

Tadmor (gain) vs. Tapawera Bridge (loss)

Date

20/02/06 27/02/06 6/03/06 13/03/06 20/03/06 27/03/06 3/04/06

Tem

pera

ture

(oC

)

12

14

16

18

20

22

24

Dis

char

ge (m

3 s-1)

0

10

20

30

40

Tapawera Bridge_Loss Tadmor_Gain Discharge - Gorge+Motupiko

RecessionBase flow Base flow

ICM1 (gaining) vs. ICM3 (losing)

Date20/02/06 27/02/06 6/03/06 13/03/06 20/03/06 27/03/06 3/04/06

Tem

pera

ture

(oC

)

10

12

14

16

18

20

22

24

Dis

char

ge (m

3 s-1

)

0

10

20

30

40

50

ICM3_Loss ICM1_Gain Flow Gorge+Motupiko

RecessionBase flow Base flow

Tadmor vs Tapawera Bridge

o Differences greatest during baseflow– Highest relative contribution of GW– Differs between sites

How much does GW contribute to SW?–Simple mixing models

Mixing model on temperature data

10

12

14

16

18

20

22

24

1

Tem

p (C

)

Predicted at 10%Observed

10

12

14

16

18

20

22

1

Tem

p (C

)

Predicted at 20%Observed

o Predicting mixed water from temps in cold and upstream

Mixing models

o Mixing model suggests potential for 10-20% of water at site is from cold source (GW)

o As much as 0.5 m3/so 30% gain predicted by model for

whole reach

Longitudinal surveys

o Drifted ~14 km of river• spot readings

– Pools» Head, deep water, edges

– Tributaries– Backwaters

Longitudinal surveys

Backwater

River: 20.9ºC, 133 µS/cm, 11.31 mg/l (126% sat)

Springs: 17.3ºC, 107 µS/cm, 9.2 mg/l (96% sat)

Backwater

River: 20.5ºC, 132 µS/cm, 10.39 mg/l (114.8% sat)

Springs: 17.0ºC, 132 µS/cm, 4.9 – 8.5 mg/l (56-88% sat)

Summary

Groundwater model• patchy gaining and losing reaches (km+

scale)

Temperature loggers• Up to 3.5ºC difference between some

gaining and loosing• GW contributes c.10-20% of baseflow

Summary

Longitudinal survey• No stratification• Few obvious upwellings – limited area• Lateral springs

– Up to ~3.5ºC cooler than mainstem– Too shallow for trout– Abundant native fish

The big picture – Motueka ICM

o Integration between disciplines has allowed data gathering of mutual benefit

o Temperature data has and will add to understanding of groundwater-river interaction

o Modelling beneficial for river ecology planning (and vice versa)