Ground Water – Surface Water Ground Water – Surface Water InteractionsInteractions

(with a special emphasis on wetlands)(with a special emphasis on wetlands)

Michael R RosenMichael R Rosen

Carson CityCarson City

Ground Water is Linked to Ground Water is Linked to Surface Water by:Surface Water by:

• Ground Water - Recharge from rivers, Lakes, Ground Water - Recharge from rivers, Lakes, wetlands & seawaterwetlands & seawater• Surface Water - Recharge from springs, seeps & Surface Water - Recharge from springs, seeps & subterranean flowsubterranean flow

This means that both must be managed togetherThis means that both must be managed together

The linkages are complexThe linkages are complex

Groundwater is important Groundwater is important because:because:

• It provides water for rivers, streams It provides water for rivers, streams and wetlandsand wetlands

• It provides a water resource for It provides a water resource for humans, stock and plants (irrigation)humans, stock and plants (irrigation)

• It helps maintain lake water levelsIt helps maintain lake water levels• It can provide a pathway to filter, It can provide a pathway to filter,

chemically sequester or remove chemically sequester or remove contaminants (but not always!)contaminants (but not always!)

Some Basic HydraulicsSome Basic Hydraulics(based on wetland hydrology – (based on wetland hydrology –

but could be applied but could be applied to other surface water interactions)to other surface water interactions)

Recharge to Recharge to surface watersurface water(ground water sink)(ground water sink)

Recharge to ground waterRecharge to ground water(connected flow)(connected flow)

Possible recharge to Possible recharge to ground waterground water

(disconnected from water table - Perched)(disconnected from water table - Perched)

Through flowThrough flow

Through flow to River Through flow to River through a wetlandthrough a wetland

Coastal dischargeCoastal discharge

High tide

Low tide

HydraulicsHydraulicsquestionsquestions

• Which types of wetland will be most Which types of wetland will be most effective for contaminant removal?effective for contaminant removal?

• Which types of wetlands are most Which types of wetlands are most easily engineered?easily engineered?

• How do coastal wetlands differ from How do coastal wetlands differ from other types of wetlandsother types of wetlands

Techniques for measuring Techniques for measuring GW-SW interactionGW-SW interaction

• Stream Losses Stream Losses (discharge relationships at two (discharge relationships at two points in a river channel)points in a river channel)• Not easy to do in a braided riverNot easy to do in a braided river

• Ground water level measurements Ground water level measurements (after recharge events in the river)(after recharge events in the river)• May not be locally derivedMay not be locally derived

• Chemical and isotopic measurementsChemical and isotopic measurements• May not be quantitativeMay not be quantitative

• Measurements of SpringsMeasurements of Springs • Not always easy to doNot always easy to do

Techniques for measuring Techniques for measuring GW-SW interactionGW-SW interaction

• River sedimentary processes River sedimentary processes ((Changes Changes in sedimentation rate in different reaches of the in sedimentation rate in different reaches of the river)river)• Expensive to doExpensive to do

• ModellingModelling• Analytical solutionsAnalytical solutions

• Fewer assumptions but still a modelFewer assumptions but still a model

• Spatial solutions (MODFLOW etc)Spatial solutions (MODFLOW etc)• More assumptions are needed to make these More assumptions are needed to make these

techniques worktechniques work

Wetlands and the Wetlands and the Hydrologic CycleHydrologic Cycle

• Land useLand use

• Groundwater Groundwater chemical chemical

transporttransport

• DischargeDischarge

Land UseLand Use

What sorts of effects from:What sorts of effects from:• Agriculture – Agriculture – • Horticulture – Horticulture – • Urban development – Urban development – • Deforestation – Deforestation – • Afforestation – Afforestation – • Industrialisation – Industrialisation – • Undeveloped land –Undeveloped land –

Land Use Land Use QuestionsQuestions

• What sorts of land use are What sorts of land use are compatible with wetlands?compatible with wetlands?

• What sorts of land uses should What sorts of land uses should be avoided?be avoided?

• How do land uses change the How do land uses change the hydrologic cycle of wetlands?hydrologic cycle of wetlands?

Groundwater Groundwater chemical chemical transporttransport

• Conservative tracers – Not many Conservative tracers – Not many under wetland conditions due to under wetland conditions due to high organic content of “soils”high organic content of “soils”

• Cl is one possibility Cl is one possibility

• Br however is likely to be adsorbedBr however is likely to be adsorbed

Groundwater Groundwater chemical transport: chemical transport: Possible chemical Possible chemical conditions of the conditions of the

waterwater

• ReducingReducing

• Anaerobic Anaerobic

• Both or one or the otherBoth or one or the other

N transformations in N transformations in groundwater groundwater

(under anaerobic conditions)(under anaerobic conditions)

Denitrification:Denitrification:

4NO4NO33-- + 5CH + 5CH22O = 2NO = 2N2(g)2(g) + 5HCO + 5HCO33

--

Dissimilatory nitrate reduction:Dissimilatory nitrate reduction:

NONO33- - + H + H22O + 2CHO + 2CH22O = NHO = NH44

++ + 2HCO + 2HCO33--

CHCH22O represents organic matterO represents organic matter

0.02 0.04 0.06 0.08 0.10 0.120.00

0.05

0.10

0.15

0.20

NH

4-N

mea

ns

of

gro

un

dw

ater

(g

/m3 )

NO3-N means of groundwater (g/m3)

0 20 40 60 80 100

60

120

180

240

P1

P2

P3

P4P5

P6

P7

P8

P9

HC

O3 m

ean

s o

f p

iezo

met

ers

(g/m

3 )

Fe means of piezometers (g/m3

)

0 20 40 60 80 1006.1

6.2

6.3

6.4

6.5

6.6

6.7

6.8

6.9

7.0

P1P2

P3

P4 P5P6

P7P8

P9

p

H

Fe means of piezometers (g/m3)

CHCH33COOH + 8 Fe(OH)COOH + 8 Fe(OH)33 + 14 H + 14 H++

8 Fe8 Fe+2+2 + 2 HCO + 2 HCO33

-- + 20 H + 20 H22O O

(Hite and Cheng, 1996)(Hite and Cheng, 1996)

0 20 40 60 80 1000

2

4

6

8

10

12

P1

P2

P3

P4

P5

P6

P7

P8

P9

SO

4 mea

ns

of

pie

zom

eter

s (g

/m3 )

Fe means of piezometers (g/m3)

0 20 40 60 80 1000.0

0.1

0.2

0.3

0.4

0.5

R2 = 0.98

M

ean

Ele

ctri

cal C

on

du

ctiv

ity

(mS

/cm

)

Mean Total Dissolved Iron (g/m3)

Chemical transport Chemical transport questionsquestions

• What types of chemical reactions are What types of chemical reactions are helpful in determining sinks and losses in a helpful in determining sinks and losses in a wetland system?wetland system?• What field parameters are helpful in What field parameters are helpful in determining the chemical condition of the determining the chemical condition of the wetland? wetland? • How can chemistry be used to determine How can chemistry be used to determine the effectiveness of wetlands in preventing the effectiveness of wetlands in preventing contamination?contamination?

DischargeDischarge

• What happens when What happens when groundwater and surface water groundwater and surface water is discharged from a wetland? is discharged from a wetland?

peat

s and

gro undwater flo w

reduc ingc onditio ns

beginbeac h ridge

feo utletgro undwater

flo w

LAKE TAUPOLAKE TAUPO

2+

N o t to s c a le

Iron StainIron Stain

Flood remediationFlood remediation

• Wetlands as temporary storage Wetlands as temporary storage of flood watersof flood waters

• Natural systemsNatural systems• South Taupo WetlandsSouth Taupo Wetlands

• Engineered systemsEngineered systems• Lower Waikato to prevent Lower Waikato to prevent

flooding of the Waikato Riverflooding of the Waikato River• Urban wetlands for peak flows Urban wetlands for peak flows

Flood remediationFlood remediationquestionsquestions

• Should wetlands be engineered for Should wetlands be engineered for flood remediation? (i.e. should we view flood remediation? (i.e. should we view them as an engineering opportunity?)them as an engineering opportunity?)

• When do the benefits of not having When do the benefits of not having flood remediation wetlands outweigh flood remediation wetlands outweigh having them?having them?

• Reclaiming wetlands – is it economic?Reclaiming wetlands – is it economic?

Wetland FunctionsWetland Functions

• Habitat for plants and animalsHabitat for plants and animals

• Improves quality of water passingImproves quality of water passing through itthrough it

• RecreationRecreation

• Global scale climate - Global scale climate - carbon sink, air-humiditycarbon sink, air-humidity

South Taupo WetlandsSouth Taupo WetlandsAs an example of GW – SWAs an example of GW – SW

InteractionsInteractions• Ecological threatsEcological threats

• Ground water quality studies Ground water quality studies & & Water balance for Lake TaupoWater balance for Lake Taupo

• Sediment studiesSediment studies

• Hydraulic studiesHydraulic studies

15 kmMt. RuapehuElev. 2800 m

Mt. NgauruhoeElev. 2290 m

Mt. TongariroElev. 1986 m

Elev. 1660 m

Elev. 1440 m

Kaim

anaw

a Ran

ge

Hau

hung

a R

oa R

ange

N

Taupo

Catchment Area

Lake TaupoElev. 357 m

Turangi

Lake

Taupo

Out

let

B o atram p W a i m a r i n o R

M o tuo ap a

STA

TE H

IGH

WAY

1

Waio

ta ka R

L ag o o nB eac h R idge

T h e C r e e k

P 7P 8P 9

P 1

P 4P 5

P 6

P 2

P 3

P 10

P 11P 12

Waih i B ay

To kaanu B ay

M aketu Is land

J o n esIs lan d

T o k a a n u S t r e a mS

. H.4 1

T o k a a n u T a i l r a c e Ca n a l

L A K E T A U P O

Stum p B ay

To kaanu

P iezo meters

E xtent o f theS outh TaupoWetland H angarito

c hannel

o xid atio np o nds Turan g i

A irs

trip

D e L ato urs P o o l

1 km

N

G rac ie s P o o l

Stewart Island

N O R T HIS LA N D

S O U T HIS LA N D

Wellingto n

S outh Taupo Wetland

A uckland

VegetationVegetation

• 12 - 14 plant communities identified (see map)12 - 14 plant communities identified (see map)• A total area of 1552 ha was mappedA total area of 1552 ha was mapped• 1/2 of 12 vegetation classes dominated by exotic 1/2 of 12 vegetation classes dominated by exotic

species and cover 1/2 of the wetland (including pasture) species and cover 1/2 of the wetland (including pasture) or 1/3 (excluding pasture)or 1/3 (excluding pasture)

• Largest plant community - Pasture, followed by Largest plant community - Pasture, followed by manuka, shrubland (willows), and blackberrymanuka, shrubland (willows), and blackberry

• Low stature vegetation dominated by raupo, flax and Low stature vegetation dominated by raupo, flax and BaumeaBaumea sedgelands sedgelands

WillowsWillows

• 183 ha was invaded by Crack willow 183 ha was invaded by Crack willow (mostly located on river banks, lake (mostly located on river banks, lake edges and flood prone areas)edges and flood prone areas)

• 432 ha was invaded by Grey willow 432 ha was invaded by Grey willow throughout the wetland (almost 1/3 of throughout the wetland (almost 1/3 of the wetland) the wetland)

Ecological Threats to the Ecological Threats to the WetlandWetland

• Only 20% of the wetland is Only 20% of the wetland is “protected”“protected”

• Invasion of Grey WillowInvasion of Grey Willow

• Changes in lake level effects Changes in lake level effects distribution of plant communitiesdistribution of plant communities

• Frequent fires (caused by humans)Frequent fires (caused by humans)

Ground water quality Ground water quality studies & studies &

Water Balance for Lake Water Balance for Lake TaupoTaupo

Previous water balance calculations

Inflow = Outflow + change in storage

or

Isurf + Isub + PL = OL + (V1-V2) + EL

Where

Isurf = Surface inflows (rivers and streams)

Isub = Subsurface inflows (groundwater)

PL = Direct precipitation on the lake

OL = Outflow through the control gates

(V1-V2) = change in lake storage

EL = Open water evaporation

(Schouten, 1980)

Previous water balance calculations

Inflow = Outflow + change in storage

in m3 s-1

Isurf (131) + Isub (??) + PL (25) = OL (146) + (V1-V2) (5) + EL (13)

Which equals

Isub = 164 - 156

Isub = 8 m3 s-1 +/- 5 m3 s-1

or

5% of the total budget

(Schouten, 1980)

Recent groundwater research in Taupo

• Effect of forestry on Waimarino River groundwater - GNS

• Effect of Turangi waste water on groundwater - GNS

• South Taupo Wetland - GNS, VUW

• Waitahanui groundwater study - EW

• Acacia Bay groundwater study - GNS

• Western Bays groundwater study - EW, GNS • Age of water in Mapara St.- EW, GNS

Groundwater Measurements

Measured concentration of

Nitrogen in Taupo Groundwater • At Acacia Bay = 0.5 - 4.5 mg/L NO3-N

• At Waitahanui = 0.7 - 8 mg/L NO3-N

• At Turangi = 0 - 25 mg/L NH4-N

• At Waimarino = 0 - 2 mg/L NH4-N

• At Taupo (old data) = 0.4 - 7 mg/L NO3-N

• At Western Bays = 1.45 mg/L NO3-N1998 NO3-N concentration in Lake Taupo was:0.0012 - 0.0291 mg/L

N mass calculations

Isurf (131) x N conc. + Isub (8) x N conc. + PL (25) x N conc. = Mass of N entering the Lake

Isurf (131) x 0.25 mg/L NO3-N = 33 g/sec(from Schouten 1980)

+ Isub (8) x 1 mg/L (conservative est.) = 8 g/sec. + PL (25) x 0.01 mg/L = 0.25 g/sec

Total N input = 41.25 g/sec

Based on these calculations: Groundwater accounts for

20% of N inputs to lake

If groundwater N were to double, groundwater would contribute

32% of N to lake

What does this mean for land use intensification?

What does all this mean for Lake managers?

• Groundwater flow and N contributions are significant in the Taupo Groundwater flow and N contributions are significant in the Taupo basin even if groundwater accounts for only basin even if groundwater accounts for only 5%5% flow input to the flow input to the lake it is currently lake it is currently 20%20% of N load. of N load.

• There is a significant risk of deteriorating lake water quality if land There is a significant risk of deteriorating lake water quality if land use instensification is allowed to proceed without careful controls use instensification is allowed to proceed without careful controls and monitoringand monitoring

What does all this mean for Lake managers? (cont)

• Wetlands are an important part of the N budget and ecological Wetlands are an important part of the N budget and ecological health of the Taupo Basin. health of the Taupo Basin.

• Wetland preservation and establishment should be encouraged Wetland preservation and establishment should be encouraged around the lake and along rivers. around the lake and along rivers. However: However:

• Wetlands help remove N from the shallow groundwater, but deeper Wetlands help remove N from the shallow groundwater, but deeper groundwater may pass through wetlands uneffected.groundwater may pass through wetlands uneffected.

More Groundwater N and flow data are needed

• Current study in Western Bays is helping

• Long-term monitoring is needed to determine trends

• Better estimates of groundwater quantities are needed

• Investigations into the current sources of N would help determine what future intensification of land use will do to the N budget of the basin

Although more groundwater data are needed to accurately determine the N budget

A precautionary approach should be maintained because once

groundwater quality deteriorates, Lake water quality is not far

behind

Groundwater FindingsGroundwater Findings

• Low Concentrations of All Measured Nutrients are found in STW

• High Concentrations of Iron (up to 160 g/m3) Leads to a Reddish-Brown Colour of Surface Water and Staining of Sediment at the Surface Water - Groundwater Interface

• High Organic Content in STW groundwater

Wetland Wetland HydraulicsHydraulics

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec356200

356300

356400

356500

356600

356700

356800

356900

357000

357100

357200

357300

357400

Max 1906-1940 Max 1942-1996

lake

leve

l (m

m a

sl)

month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec356000

356100

356200

356300

356400

356500

356600

356700

356800

356900

357000

357100

357200

Min 1906-1940 Min 1942-1996

lake

leve

l (m

m a

sl)

month

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

356100

356200

356300

356400

356500

356600

356700

356800

356900

357000

357100

357200

357300

Mean 1906-1940 Mean 1942-1996

lake

leve

l (m

m a

sl)

month

If you are interested in If you are interested in further reading on the further reading on the

subjectsubject• Eser, P. & Rosen, M.R., 2000, Effects of artificial Eser, P. & Rosen, M.R., 2000, Effects of artificial

lake level control of Lake Taupo, North Island, lake level control of Lake Taupo, North Island, New Zealand, on the Stump Bay wetland. New Zealand, on the Stump Bay wetland. New New Zealand Journal of Marine and Freshwater Zealand Journal of Marine and Freshwater ResearchResearch, 34, 217-230., 34, 217-230.

• Eser, P. & Rosen, M.R., 1999, The influence of Eser, P. & Rosen, M.R., 1999, The influence of groundwater hydrology and stratigraphy on the groundwater hydrology and stratigraphy on the hydrochemistry of Stump Bay, South Taupo hydrochemistry of Stump Bay, South Taupo Wetland, New Zealand. Wetland, New Zealand. Journal of Hydrology, Journal of Hydrology,

220220, , 27-47.27-47.